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1. HS 432 Ventilation Chapters 19, 20 Ventilation
If too little outdoor air enters your facility, pollutants can accumulate to a level that can pose health and discomfort problems for your employees. Unless they are built with special mechanical means of ventilation, facilities that are designed and constructed to minimize the amount of outside air that can leak into and out of the facility may have higher pollutant levels. However, because some weather conditions can drastically reduce the amount of outside air that enters your facility, pollutants can build up in facilities that are normally considered leaky.
Ventilation is defined as the process of supplying air to, or removing air from, any space by natural or mechanical means. General ventilation uses the movement of air within the general work space to displace or dilute contaminants with fresh outside air. General ventilation of the workplace also contributes to the comfort and efficiency of employees because working under extreme conditions of temperature and humidity may have an adverse effect on employee productivity and health.
In the last several years, a growing body of scientific evidence has indicated that the air within our working environments can be more seriously polluted than the outdoor air, even in the largest and most industrialized cities. The levels of air pollution from individual sources may not pose a significant risk to health by themselves, but most working environments have more than one source that contributes to indoor air pollution. Fortunately, steps can be taken to both reduce the risk from existing sources of indoor air pollution, and prevent new sources from occurring.
Effects
Health effects from indoor air pollutants fall into two categories:
Those that are experienced immediately after exposure; and
Those that do not show up until years later.
Immediate effects, which can show up after a single exposure or repeated exposures, include irritation of the eyes, nose, throat, headaches, dizziness, and fatigue. These immediate effects are usually short-term and treatable. Sometimes, the prescribed treatment is simply to eliminate the person’s exposure to the source of the pollution, if the source can be identified. Symptoms of some diseases, such as asthma, can show up soon after exposure to some indoor air pollutants.
The likelihood of an individual developing immediate reactions to indoor air pollutants depends on several factors, such as age and pre-existing medical conditions. In other cases, whether a person reacts to a pollutant can be determined by individual sensitivity, which varies from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well.
Certain immediate effects are similar to those from colds or other viral diseases, so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution or some other factors. For this reason, it is important to pay attention to the time and place the symptoms occur. If the symptoms fade or go away when an employee is away from work, and return when the employee returns to work, an effort should be made to identify indoor air sources at the worksite that may be possible causes.
Some effects may be made worse by an inadequate supply of outside air or from the heating, cooling, or humidity conditions prevailing in the facility. Other health effects may show up either years after the exposure has occurred, or only after long or repeated periods of exposure. These effects, which include respiratory diseases, heart disease, and cancer, can be severely debilitating or even fatal.
Legionnaire’s disease is also a concern for those who work indoors. The bacteria Legionella causes the respiratory illness Legionnaire’s disease and was first recognized in 1976 during an epidemic of pneumonia, which affected persons attending an American Legion convention. Persons with Legionnaire’s disease typically have respiratory symptoms, and often have headaches, confusion, and sometimes diarrhea.
Some health effects can be useful indicators of poor ventilation that can lead to an indoor air quality problem. If you think employees have symptoms that may be related to the working environment, you should discuss this with your health and safety personnel. Ventilation
If too little outdoor air enters your facility, pollutants can accumulate to a level that can pose health and discomfort problems for your employees. Unless they are built with special mechanical means of ventilation, facilities that are designed and constructed to minimize the amount of outside air that can leak into and out of the facility may have higher pollutant levels. However, because some weather conditions can drastically reduce the amount of outside air that enters your facility, pollutants can build up in facilities that are normally considered leaky.
Ventilation is defined as the process of supplying air to, or removing air from, any space by natural or mechanical means. General ventilation uses the movement of air within the general work space to displace or dilute contaminants with fresh outside air. General ventilation of the workplace also contributes to the comfort and efficiency of employees because working under extreme conditions of temperature and humidity may have an adverse effect on employee productivity and health.
In the last several years, a growing body of scientific evidence has indicated that the air within our working environments can be more seriously polluted than the outdoor air, even in the largest and most industrialized cities. The levels of air pollution from individual sources may not pose a significant risk to health by themselves, but most working environments have more than one source that contributes to indoor air pollution. Fortunately, steps can be taken to both reduce the risk from existing sources of indoor air pollution, and prevent new sources from occurring.
Effects
Health effects from indoor air pollutants fall into two categories:
Those that are experienced immediately after exposure; and
Those that do not show up until years later.
Immediate effects, which can show up after a single exposure or repeated exposures, include irritation of the eyes, nose, throat, headaches, dizziness, and fatigue. These immediate effects are usually short-term and treatable. Sometimes, the prescribed treatment is simply to eliminate the person’s exposure to the source of the pollution, if the source can be identified. Symptoms of some diseases, such as asthma, can show up soon after exposure to some indoor air pollutants.
The likelihood of an individual developing immediate reactions to indoor air pollutants depends on several factors, such as age and pre-existing medical conditions. In other cases, whether a person reacts to a pollutant can be determined by individual sensitivity, which varies from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well.
Certain immediate effects are similar to those from colds or other viral diseases, so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution or some other factors. For this reason, it is important to pay attention to the time and place the symptoms occur. If the symptoms fade or go away when an employee is away from work, and return when the employee returns to work, an effort should be made to identify indoor air sources at the worksite that may be possible causes.
Some effects may be made worse by an inadequate supply of outside air or from the heating, cooling, or humidity conditions prevailing in the facility. Other health effects may show up either years after the exposure has occurred, or only after long or repeated periods of exposure. These effects, which include respiratory diseases, heart disease, and cancer, can be severely debilitating or even fatal.
Legionnaire’s disease is also a concern for those who work indoors. The bacteria Legionella causes the respiratory illness Legionnaire’s disease and was first recognized in 1976 during an epidemic of pneumonia, which affected persons attending an American Legion convention. Persons with Legionnaire’s disease typically have respiratory symptoms, and often have headaches, confusion, and sometimes diarrhea.
Some health effects can be useful indicators of poor ventilation that can lead to an indoor air quality problem. If you think employees have symptoms that may be related to the working environment, you should discuss this with your health and safety personnel.
2. Objectives Describe different types of ventilation systems
Describe different components of a ventilation system
Describe design criteria Causes
While pollutants commonly found in indoor air can be responsible for many harmful effects, there is considerable uncertainty about what concentrations or periods of exposure are necessary to produce specific adverse health effects. Further research is needed to better understand which health effects can occur after exposure to the low-level pollutant concentrations as well as higher-level concentrations.
There are two primary causes of indoor air quality problems: indoor sources of air pollution and improper ventilation of your facility. Indoor pollution sources release gases or particles into the air and are the primary cause of indoor air quality problems. Inadequate ventilation can also increase indoor pollutant levels by not bringing in sufficient outside air to dilute emissions from indoor sources, and by not carrying indoor air pollutants out of your facility. High temperature and humidity levels can also increase concentrations of some pollutants.
Another way to judge whether your facility has or could develop indoor air problems is to identify potential sources of indoor air pollution. Although the presence of such sources does not necessarily mean that you have an indoor air quality problem, being aware of the type and number of potential sources is an important step toward assessing the quality of air in your workplace.
A third way to decide whether your workplace may have poor indoor air quality is to look for signs that there are airflow problems throughout your facility. Some things that could indicate that your workplace may have an indoor air quality problem include:
Stuffy air;
Dirty central heating equipment;
Dirty central air conditioning equipment; and
Moisture condensation on windows or walls.
In addition, your facility’s ventilation system should be checked to ensure that it is operating properly. Ventilation systems should do a number of different things, including:
Preventing the degradation of workplace air by carbon dioxide buildup, biological organisms, odors, and heat.
Providing makeup air that replaces air that has been exhausted outside.
Heating replacement air through industrial heating processes, such as oil, gas, or steam.
Whenever employee exposure, without regard to the use of respirators, exceeds the permissible exposure limits (PELs) of the air contaminants rule, a local exhaust ventilation system must be provided and used to maintain employee exposures within the prescribed limits.
Causes
While pollutants commonly found in indoor air can be responsible for many harmful effects, there is considerable uncertainty about what concentrations or periods of exposure are necessary to produce specific adverse health effects. Further research is needed to better understand which health effects can occur after exposure to the low-level pollutant concentrations as well as higher-level concentrations.
There are two primary causes of indoor air quality problems: indoor sources of air pollution and improper ventilation of your facility. Indoor pollution sources release gases or particles into the air and are the primary cause of indoor air quality problems. Inadequate ventilation can also increase indoor pollutant levels by not bringing in sufficient outside air to dilute emissions from indoor sources, and by not carrying indoor air pollutants out of your facility. High temperature and humidity levels can also increase concentrations of some pollutants.
Another way to judge whether your facility has or could develop indoor air problems is to identify potential sources of indoor air pollution. Although the presence of such sources does not necessarily mean that you have an indoor air quality problem, being aware of the type and number of potential sources is an important step toward assessing the quality of air in your workplace.
A third way to decide whether your workplace may have poor indoor air quality is to look for signs that there are airflow problems throughout your facility. Some things that could indicate that your workplace may have an indoor air quality problem include:
Stuffy air;
Dirty central heating equipment;
Dirty central air conditioning equipment; and
Moisture condensation on windows or walls.
In addition, your facility’s ventilation system should be checked to ensure that it is operating properly. Ventilation systems should do a number of different things, including:
Preventing the degradation of workplace air by carbon dioxide buildup, biological organisms, odors, and heat.
Providing makeup air that replaces air that has been exhausted outside.
Heating replacement air through industrial heating processes, such as oil, gas, or steam.
Whenever employee exposure, without regard to the use of respirators, exceeds the permissible exposure limits (PELs) of the air contaminants rule, a local exhaust ventilation system must be provided and used to maintain employee exposures within the prescribed limits.
3. Ventilation Natural
Open a window
Not the best type for an industrial setting
Mechanical
Any ventilation system which moves air by mechanical means
Usually Fans Ventilation is defined as the process of supplying air to, or removing air from, any space by natural or mechanical means. General ventilation uses the movement of air within the general work space to displace or dilute contaminants with fresh outside air. General ventilation of the workplace also contributes to the comfort and efficiency of employees because working under extreme conditions of temperature and humidity may have an adverse effect on employee productivity and health.
In the last several years, a growing body of scientific evidence has indicated that the air within our working environments can be more seriously polluted than the outdoor air, even in the largest and most industrialized cities. The levels of air pollution from individual sources may not pose a significant risk to health by themselves, but most working environments have more than one source that contributes to indoor air pollution. Fortunately, there are steps that you can take to both reduce the risk from existing sources of indoor air pollution, and to prevent new sources from occurring.
There are two primary causes of indoor air quality problems: indoor sources of air pollution and improper ventilation of your facility. Indoor pollution sources release gases or particles into the air and are the primary cause of indoor air quality problems. Inadequate ventilation can also increase indoor pollutant levels by not bringing in sufficient outside air to dilute emissions from indoor sources, and by not carrying indoor air pollutants out of your facility. High temperature and humidity levels can also increase concentrations of some pollutants.
Ventilation is defined as the process of supplying air to, or removing air from, any space by natural or mechanical means. General ventilation uses the movement of air within the general work space to displace or dilute contaminants with fresh outside air. General ventilation of the workplace also contributes to the comfort and efficiency of employees because working under extreme conditions of temperature and humidity may have an adverse effect on employee productivity and health.
In the last several years, a growing body of scientific evidence has indicated that the air within our working environments can be more seriously polluted than the outdoor air, even in the largest and most industrialized cities. The levels of air pollution from individual sources may not pose a significant risk to health by themselves, but most working environments have more than one source that contributes to indoor air pollution. Fortunately, there are steps that you can take to both reduce the risk from existing sources of indoor air pollution, and to prevent new sources from occurring.
There are two primary causes of indoor air quality problems: indoor sources of air pollution and improper ventilation of your facility. Indoor pollution sources release gases or particles into the air and are the primary cause of indoor air quality problems. Inadequate ventilation can also increase indoor pollutant levels by not bringing in sufficient outside air to dilute emissions from indoor sources, and by not carrying indoor air pollutants out of your facility. High temperature and humidity levels can also increase concentrations of some pollutants.
4. When Do You Use Mechanical Ventilation? Must conform with standards incorporated by reference e.g.
ANSI
NFPA
ACGIH
Draw the flow
of air into a
hood or
exhaust duct Ventilation systems are designed to do all of the following except:
A) Supply oxygen
B) Remove contaminants
C) Provide comfort
D) Produce energy
The correct answer is: D
The purpose of ventilation includes dilution of contaminants and supplying make up air. Ventilation systems generally use energy rather than produce energy.
Ventilation systems are designed to do all of the following except:
A) Supply oxygen
B) Remove contaminants
C) Provide comfort
D) Produce energy
The correct answer is: D
The purpose of ventilation includes dilution of contaminants and supplying make up air. Ventilation systems generally use energy rather than produce energy.
5. Ventilation Industrial ventilation
Generally involves the use of supply and exhaust ventilation to control emissions, exposures, and chemical hazards in the workplace
Non-industrial ventilation systems commonly known as
heating, ventilating,
and air-conditioning
(HVAC) systems
Traditionally were built
to control temperature,
humidity, and odors The most common cause of indoor air quality problems is:
A) Off-gassing from building materials and furnishings
B) Cigarette smoking
C) Processes using volatile chemicals
D) Poor ventilation
The correct answer is: D
Poor ventilation is the most common cause of indoor air quality problems because air contaminants from sources such as cigarette smoke, processes, and off-gassing build-up can cause hypersensitivity in employees. The other answers contribute to the cause, but poor ventilation is usually the root of the problem.The most common cause of indoor air quality problems is:
A) Off-gassing from building materials and furnishings
B) Cigarette smoking
C) Processes using volatile chemicals
D) Poor ventilation
The correct answer is: D
Poor ventilation is the most common cause of indoor air quality problems because air contaminants from sources such as cigarette smoke, processes, and off-gassing build-up can cause hypersensitivity in employees. The other answers contribute to the cause, but poor ventilation is usually the root of the problem.
6. Ventilation System Types Dilution and removal by general exhaust
Local exhaust
Makeup air
Replacement
HVAC
Primarily for comfort
Ducts are square
Recirculation systems
Ventilation systems generally involve a combination of these types of systems. For example, a large local exhaust system may also serve as a dilution system, and the HVAC system may serve as a makeup air system
HVAC (heating, ventilating, and air-conditioning) is a common term that can also include cooling, humidifying or dehumidifying, or otherwise conditioning air for comfort and health. HVAC also is used for odor control and the maintenance of acceptable concentrations of carbon dioxide.
Air-conditioning has come to include any process that modifies the air for a work or living space: heating or cooling, humidity control, and air cleaning. Historically, air-conditioning has been used in industry to improve or protect machinery, products, and processes. The conditioning of air for humans has become normal and expected. Although the initial costs of air conditioning are high, annual costs may account only for about 1% to 5% of total annual operating expenses. Improved human productivity, lower absenteeism, better health, and reduced housekeeping and maintenance almost always make air-conditioning cost effective.
Mechanical air-handling systems can range from simple to complex. All distribute air in a manner designed to meet ventilation, temperature, humidity, and air-quality requirements established by the user. Individual units may be installed in the space they serve, or central units can serve multiple areas.
HVAC engineers refer to the areas served by an air handling system as zones. The smaller the zone, the greater the likelihood that good control will be achieved; however, equipment and maintenance costs are directly related to the number of zones. Some systems are designed to provide individual control of rooms in a multiple-zone system.
Both the provision and distribution of make-up air are important to the proper functioning of the system. The correct amount of air should be supplied to the space. Supply registers should be positioned to avoid disruption of emission and exposure controls and to aid dilution efforts.
Considerations in designing an air-handling system include volume flow rate, temperature, humidity, and air quality. Equipment selected must be properly sized and may include:
outdoor air plenums or ducts
filters
supply fans and supply air systems
heating and cooling coils
humidity control equipment
supply ducts
distribution ducts, boxes, plenums, and registers
dampers
return air plenums
exhaust air provisions
return fans
controls and instrumentation Ventilation systems generally involve a combination of these types of systems. For example, a large local exhaust system may also serve as a dilution system, and the HVAC system may serve as a makeup air system
HVAC (heating, ventilating, and air-conditioning) is a common term that can also include cooling, humidifying or dehumidifying, or otherwise conditioning air for comfort and health. HVAC also is used for odor control and the maintenance of acceptable concentrations of carbon dioxide.
Air-conditioning has come to include any process that modifies the air for a work or living space: heating or cooling, humidity control, and air cleaning. Historically, air-conditioning has been used in industry to improve or protect machinery, products, and processes. The conditioning of air for humans has become normal and expected. Although the initial costs of air conditioning are high, annual costs may account only for about 1% to 5% of total annual operating expenses. Improved human productivity, lower absenteeism, better health, and reduced housekeeping and maintenance almost always make air-conditioning cost effective.
Mechanical air-handling systems can range from simple to complex. All distribute air in a manner designed to meet ventilation, temperature, humidity, and air-quality requirements established by the user. Individual units may be installed in the space they serve, or central units can serve multiple areas.
HVAC engineers refer to the areas served by an air handling system as zones. The smaller the zone, the greater the likelihood that good control will be achieved; however, equipment and maintenance costs are directly related to the number of zones. Some systems are designed to provide individual control of rooms in a multiple-zone system.
Both the provision and distribution of make-up air are important to the proper functioning of the system. The correct amount of air should be supplied to the space. Supply registers should be positioned to avoid disruption of emission and exposure controls and to aid dilution efforts.
Considerations in designing an air-handling system include volume flow rate, temperature, humidity, and air quality. Equipment selected must be properly sized and may include:
outdoor air plenums or ducts
filters
supply fans and supply air systems
heating and cooling coils
humidity control equipment
supply ducts
distribution ducts, boxes, plenums, and registers
dampers
return air plenums
exhaust air provisions
return fans
controls and instrumentation
7. Types of Ventilation HVAC System
Create a comfortable environment
Replace exhausted air
Contains air inlet, filters, heating/cooling equipment, fan, ducts, grilles
Return system
Industrial Ventilation is a discipline that focuses on providing clean uncontaminated air to employees and manufacturing processes. These contaminants may include particulates, gases, vapors and/or mists. PAK/TEEM primary focus is on local exhaust ventilation.
Local exhaust ventilation captures and removes contaminants at or near the source. It is the preferred method of ventilation in that it provides a greater reduction in contamination with smaller amounts of airflow. Reducing exhaust airflow lowers operating costs including heating/cooling requirements.
In contrast, general exhaust is used to induce fresh air movement to mix with and dilute heat or contaminants in the air. This type of ventilation can be used for employee comfort or as part of an overall room/building ventilation strategy, but is not recommended as a primary method controlling toxic contaminants. Industrial Ventilation is a discipline that focuses on providing clean uncontaminated air to employees and manufacturing processes. These contaminants may include particulates, gases, vapors and/or mists. PAK/TEEM primary focus is on local exhaust ventilation.
Local exhaust ventilation captures and removes contaminants at or near the source. It is the preferred method of ventilation in that it provides a greater reduction in contamination with smaller amounts of airflow. Reducing exhaust airflow lowers operating costs including heating/cooling requirements.
In contrast, general exhaust is used to induce fresh air movement to mix with and dilute heat or contaminants in the air. This type of ventilation can be used for employee comfort or as part of an overall room/building ventilation strategy, but is not recommended as a primary method controlling toxic contaminants.
8. Types of Ventilation 2. Exhaust System
General exhaust system
Heat control
Removal of contaminants
RECIRCULATION Although not generally recommended, recirculation is an alternative to air exchanging. Where used, recirculation should incorporate air cleaners, a by-pass or auxiliary exhaust system, regular maintenance and inspection, and devices to monitor system performance. Key points to consider in the use of recirculation are shown in Table III:3-6. TABLE III:3-6
RECIRCULATION CRITERIA
Protection of employees must be the primary design consideration.
The system should remove as much of the contaminant as can economically be separated from exhaust air.
The system should not be designed simply to achieve PEL levels of exposure.
The system should never allow recirculation to significantly increase existing exposures.
Recirculation should not be used if a carcinogen is present.
The system should have fail-safe features, e.g., warning devices on critical parts, back-up systems.
Cleaning and filtering devices that ensure continuous and reliable collection of the contaminant should be used.
The system should provide a by-pass or auxiliary exhaust system for use during system failure.
The system should include feedback devices that monitor system performance, e.g., static pressure taps, particulate counters, amperage monitors.
The system should be designed not to recirculate air during equipment malfunction.
The employer should train employees in the use and operation of the system.
RECIRCULATION Although not generally recommended, recirculation is an alternative to air exchanging. Where used, recirculation should incorporate air cleaners, a by-pass or auxiliary exhaust system, regular maintenance and inspection, and devices to monitor system performance. Key points to consider in the use of recirculation are shown in Table III:3-6. TABLE III:3-6
RECIRCULATION CRITERIA
Protection of employees must be the primary design consideration.
The system should remove as much of the contaminant as can economically be separated from exhaust air.
The system should not be designed simply to achieve PEL levels of exposure.
The system should never allow recirculation to significantly increase existing exposures.
Recirculation should not be used if a carcinogen is present.
The system should have fail-safe features, e.g., warning devices on critical parts, back-up systems.
Cleaning and filtering devices that ensure continuous and reliable collection of the contaminant should be used.
The system should provide a by-pass or auxiliary exhaust system for use during system failure.
The system should include feedback devices that monitor system performance, e.g., static pressure taps, particulate counters, amperage monitors.
The system should be designed not to recirculate air during equipment malfunction.
The employer should train employees in the use and operation of the system.
9. Types of Ventilation 3. Dilution ventilation
Ventilation by adding enough air to a workspace so that any contaminant generated will be at a concentration that does not cause adverse health effects
Can only be used for slightly toxic substances
Can only be used for vapors
Not particles
10. Dilution Ventilation Selection checklist
Emission sources contain materials of relatively low hazard
The degree of hazard is related to toxicity, dose rate, and individual susceptibility
Emission sources are primarily vapors or gases, or small, respirable-size aerosols
Those not likely to settle
Emissions occur uniformly
Emissions are widely dispersed
Moderate climatic conditions prevail
Heat is to be removed from the space by flushing it with outside air
Concentrations of vapors are to be reduced in an enclosure
Portable or mobile emission sources are to be controlled General exhaust ventilation (dilution ventilation) is appropriate when:
Emission sources contain materials of relatively low hazard. (The degree of hazard is related to toxicity, dose rate, and individual susceptibility);
Emission sources are primarily vapors or gases, or small, respirable-size aerosols (those not likely to settle);
Emissions occur uniformly;
Emissions are widely dispersed;
Moderate climatic conditions prevail;
Heat is to be removed from the space by flushing it with outside air;
Concentrations of vapors are to be reduced in an enclosure; and
Portable or mobile emission sources are to be controlled.
General exhaust ventilation (dilution ventilation) is appropriate when:
Emission sources contain materials of relatively low hazard. (The degree of hazard is related to toxicity, dose rate, and individual susceptibility);
Emission sources are primarily vapors or gases, or small, respirable-size aerosols (those not likely to settle);
Emissions occur uniformly;
Emissions are widely dispersed;
Moderate climatic conditions prevail;
Heat is to be removed from the space by flushing it with outside air;
Concentrations of vapors are to be reduced in an enclosure; and
Portable or mobile emission sources are to be controlled.
11. Dilution Ventilation Use
Position exhausts as close to emission sources as possible
Use auxiliary fans for mixing
Make sure employees are upwind of the dilution zone
Add make-up air
where it will be
most effective
Use
The number of air changes per hour is the number of times one volume of air is replaced in the space per hour. In practice, replacement depends on mixing efficiency. When using dilution ventilation:
position exhausts as close to emission sources as possible;
use auxiliary fans for mixing;
make sure employees are upwind of the dilution zone; and
add make-up air where it will be most effective.
Compared to local exhaust ventilation, dilution ventilation:
A) Is more suitable for highly toxic substances
B) Is very good for ventilating point source emissions
C) Is less effected by short circuiting of exhaust
D) Uses less air than local exhaust ventilation
The correct answer is: C
General dilution ventilation is not appropriate for point source emissions or for use with highly toxic materials. In these situations local exhaust ventilation should be used. General dilution also uses more air than local exhaust ventilation. Short circuiting of exhaust (i.e. pulling air from clean areas because of poor positioning, lack of baffles, holes in the ductwork, etc.) is less critical for dilution ventilation than in local exhaust ventilation.
Dilution ventilation is:
A) Used to control a contaminant at its source
B) Used for controlling vapors having low toxicity
C) More economical than local exhaust ventilation
D) Is the first consideration for hazard control
The correct answer is: B
Dilution ventilation lowers the concentration of a contaminant by adding air to the general work area. Since the air is added to the general work area, it will not effectively control exposure to a toxic or highly toxic substance used in a specific location.
For which of the following operations would a general, or dilution, ventilation system be an appropriate means of control?
A) Evaporation of carbon disulfide in a chemistry lab
B) Evaporation of trichloroethylene from a degreaser
C) Finishing iron castings with a swing frame grinder
D) Foundry shakeout table
The correct answer is: B
Although all of these processes might better be served by local exhaust rather than general exhaust, the best answer can be determined by process of elimination. Answer A can be eliminated due to the high toxicity of carbon disulfide. Answers C and D can be eliminated since they involve the production of airborne dusts, which are poorly controlled by general ventilation. This leaves Answer B as the best answer by elimination.
All of the following are limiting factors on the use of general exhaust ventilation for protecting worker health, except:
A) The toxicity of the contaminant must be low
B) The contaminant generation rate must be known
C) The contaminant generation rate must be reasonably uniform over time
D) The vapor pressure of the contaminant must be low
The correct answer is: D
Although having a low vapor pressure would limit the rate at which vapors are generated into the workplace, this is not a necessary requirement for using general exhaust ventilation. The key element is the actual contaminant generation rate, not the vapor pressure. For example, in many cases it is possible to use general exhaust ventilation for gases.
As a rule, general exhaust ventilation is better suited to fire and explosion control than it is to worker health protection, for all of the following reasons except:
A) Allowable concentrations generally are higher for fire and explosion control
B) Generation rates are easier to predict for fire and explosion control
C) No workers are exposed to the contaminants when using general exhaust ventilation for fire and explosion control
D) Required exhaust air flows usually are lower for fire and explosion control than for worker protection
The correct answer is: B
Generation rates are usually about equally difficult to predict in both cases.
Use
The number of air changes per hour is the number of times one volume of air is replaced in the space per hour. In practice, replacement depends on mixing efficiency. When using dilution ventilation:
position exhausts as close to emission sources as possible;
use auxiliary fans for mixing;
make sure employees are upwind of the dilution zone; and
add make-up air where it will be most effective.
Compared to local exhaust ventilation, dilution ventilation:
A) Is more suitable for highly toxic substances
B) Is very good for ventilating point source emissions
C) Is less effected by short circuiting of exhaust
D) Uses less air than local exhaust ventilation
The correct answer is: C
General dilution ventilation is not appropriate for point source emissions or for use with highly toxic materials. In these situations local exhaust ventilation should be used. General dilution also uses more air than local exhaust ventilation. Short circuiting of exhaust (i.e. pulling air from clean areas because of poor positioning, lack of baffles, holes in the ductwork, etc.) is less critical for dilution ventilation than in local exhaust ventilation.
Dilution ventilation is:
A) Used to control a contaminant at its source
B) Used for controlling vapors having low toxicity
C) More economical than local exhaust ventilation
D) Is the first consideration for hazard control
The correct answer is: B
Dilution ventilation lowers the concentration of a contaminant by adding air to the general work area. Since the air is added to the general work area, it will not effectively control exposure to a toxic or highly toxic substance used in a specific location.
For which of the following operations would a general, or dilution, ventilation system be an appropriate means of control?
A) Evaporation of carbon disulfide in a chemistry lab
B) Evaporation of trichloroethylene from a degreaser
C) Finishing iron castings with a swing frame grinder
D) Foundry shakeout table
The correct answer is: B
Although all of these processes might better be served by local exhaust rather than general exhaust, the best answer can be determined by process of elimination. Answer A can be eliminated due to the high toxicity of carbon disulfide. Answers C and D can be eliminated since they involve the production of airborne dusts, which are poorly controlled by general ventilation. This leaves Answer B as the best answer by elimination.
All of the following are limiting factors on the use of general exhaust ventilation for protecting worker health, except:
A) The toxicity of the contaminant must be low
B) The contaminant generation rate must be known
C) The contaminant generation rate must be reasonably uniform over time
D) The vapor pressure of the contaminant must be low
The correct answer is: D
Although having a low vapor pressure would limit the rate at which vapors are generated into the workplace, this is not a necessary requirement for using general exhaust ventilation. The key element is the actual contaminant generation rate, not the vapor pressure. For example, in many cases it is possible to use general exhaust ventilation for gases.
As a rule, general exhaust ventilation is better suited to fire and explosion control than it is to worker health protection, for all of the following reasons except:
A) Allowable concentrations generally are higher for fire and explosion control
B) Generation rates are easier to predict for fire and explosion control
C) No workers are exposed to the contaminants when using general exhaust ventilation for fire and explosion control
D) Required exhaust air flows usually are lower for fire and explosion control than for worker protection
The correct answer is: B
Generation rates are usually about equally difficult to predict in both cases.
12. Types of Ventilation 4. Local exhaust system
Capture contaminant at source
Carries contaminant away from worker’s breathing zone
Local exhaust ventilation systems consist of five parts:
1.Hoods that draw in airborne contaminants. The exhaust system hood is the point of entry into the duct system.
2.Ducts that carry contaminated air to a central point. After contaminated air has been drawn into a hood, ducts serve the purpose of carrying that air to an air cleaner, or to the outdoors.
3.An air-cleaning device, such as a dust arrester, for purifying the air before it is discharged. Types of air cleaners include industrial air cleaners, whose purpose is to remove airborne contaminants, and air cleaners that handle relatively high rates of airflow at low static pressure.
4.A fan and motor to create the required airflow through the system.
5.A stack to disperse remaining air contaminants.
Local exhaust ventilation systems consist of five parts:
1.Hoods that draw in airborne contaminants. The exhaust system hood is the point of entry into the duct system.
2.Ducts that carry contaminated air to a central point. After contaminated air has been drawn into a hood, ducts serve the purpose of carrying that air to an air cleaner, or to the outdoors.
3.An air-cleaning device, such as a dust arrester, for purifying the air before it is discharged. Types of air cleaners include industrial air cleaners, whose purpose is to remove airborne contaminants, and air cleaners that handle relatively high rates of airflow at low static pressure.
4.A fan and motor to create the required airflow through the system.
5.A stack to disperse remaining air contaminants.
13. Local Exhaust System (1) “Local exhaust ventilation” shall mean the mechanical removal of contaminated air from the point where the contaminant is being generated or liberated.
(2) “Dilution ventilation” means inducing and mixing uncontaminated air with contaminated air in such quantities that the resultant mixture in the breathing zone will not exceed the permissible exposure limit (PEL) specified for any contaminant.
(3) “Exhaust ventilation” means the general movement of air out of the area or permit-required confined space by mechanical or natural means.
(4) “Tempered makeup air” means air which has been conditioned by changing its heat content to obtain a specific desired temperature.(1) “Local exhaust ventilation” shall mean the mechanical removal of contaminated air from the point where the contaminant is being generated or liberated.
(2) “Dilution ventilation” means inducing and mixing uncontaminated air with contaminated air in such quantities that the resultant mixture in the breathing zone will not exceed the permissible exposure limit (PEL) specified for any contaminant.
(3) “Exhaust ventilation” means the general movement of air out of the area or permit-required confined space by mechanical or natural means.
(4) “Tempered makeup air” means air which has been conditioned by changing its heat content to obtain a specific desired temperature.
14. Local Exhaust System: Components Hood
Surrounds the contaminant
Capture the contaminant
Carries the contaminant to the duct
2. Duct
Transports the contaminants through the system
Most industrial ducts are circular
3. Fan
Moves the air
4. Cleaning device
Cyclones, Electrostatic precipitators
5. Stack
Puts the air outside of the factory
Job of designing a ventilation system.
What you are really doing is figuring out
What kind of hood
How long
What kind of duct
How big should the duct be
The type of fan
How big of a fan
How much does it need to suck
Local exhaust ventilating is appropriate when:
Emission sources contain materials of relatively high hazard;
Emitted materials are primarily larger-diameter particulates (likely to settle);
Emissions vary over time;
Emission sources consist of point sources;
Employees work in the immediate vicinity of the emission source;
The plant is located in a severe climate; and
Minimizing air turnover is necessary.
Job of designing a ventilation system.
What you are really doing is figuring out
What kind of hood
How long
What kind of duct
How big should the duct be
The type of fan
How big of a fan
How much does it need to suck
Local exhaust ventilating is appropriate when:
Emission sources contain materials of relatively high hazard;
Emitted materials are primarily larger-diameter particulates (likely to settle);
Emissions vary over time;
Emission sources consist of point sources;
Employees work in the immediate vicinity of the emission source;
The plant is located in a severe climate; and
Minimizing air turnover is necessary.
15. Local Exhaust System Selection Checklist
Emission sources contain materials of relatively high hazard
Emitted materials are primarily larger-diameter particulates
Likely to settle
Emissions vary over time
Emission sources consist of point sources
Employees work in the immediate vicinity of the emission source
The plant is located
in a severe climate
Minimizing air
turnover is necessary
The basic purpose of local exhaust ventilation is to:
A) Prevent re-entrance of air contaminants
B) Remove contaminants at their source
C) Provide dilution ventilation
D) Both A) and C)
The correct answer is: B
The purpose of local exhaust ventilation is to remove the air contaminants at the source, not to dilute them.
In a local exhaust ventilation system, what quantity is preserved, from inlet to outlet?
A) Velocity
B) Volume flow
C) Static pressure
D) Mass flow
The correct answer is: D
Mass flow, which can be thought of as the number of molecules of air passing a certain point per second, is the only one of these quantities which is constant throughout a ventilation system. Volume flow can change if, for example, the temperature changes from one point to another.
In a local exhaust system, the minimum transport velocity required to keep most dusts from settling out in a duct, ranges from:
A) 500-1500 ft/min
B) 1500-2500 ft/min
C) 2500-3500 ft/min
D) 3500-4500 ft/min
The correct answer is: D
Most of the design plates in the Ventilation Manual involving dust capture specify transport velocities in this range.
The basic purpose of local exhaust ventilation is to:
A) Prevent re-entrance of air contaminants
B) Remove contaminants at their source
C) Provide dilution ventilation
D) Both A) and C)
The correct answer is: B
The purpose of local exhaust ventilation is to remove the air contaminants at the source, not to dilute them.
In a local exhaust ventilation system, what quantity is preserved, from inlet to outlet?
A) Velocity
B) Volume flow
C) Static pressure
D) Mass flow
The correct answer is: D
Mass flow, which can be thought of as the number of molecules of air passing a certain point per second, is the only one of these quantities which is constant throughout a ventilation system. Volume flow can change if, for example, the temperature changes from one point to another.
In a local exhaust system, the minimum transport velocity required to keep most dusts from settling out in a duct, ranges from:
A) 500-1500 ft/min
B) 1500-2500 ft/min
C) 2500-3500 ft/min
D) 3500-4500 ft/min
The correct answer is: D
Most of the design plates in the Ventilation Manual involving dust capture specify transport velocities in this range.
16. Ventilation Types 5. Make-up Air Systems
Exhaust ventilation systems require the replacement of exhausted air
Replacement air is often called make-up air
Can be supplied naturally
By atmospheric pressure through open doors, windows, wall louvers, and adjacent spaces
Acceptable
Through cracks in walls and windows,
beneath doors, and through roof vents
Unacceptable
Can also be provided through
dedicated replacement air systems
Generally, exhaust systems are interlocked with a dedicated make-up air system A room ventilation system has been designed to provide 5 CFM of outdoor air/person. Which statement best describes the situation?
A) The ventilation rate would be insufficient for most environments
B) The ventilation rate is sufficient for offices only
C) The room must be at least 10,000 square feet
D) The room cannot be occupied by more than 7 people
The correct answer is: A
According to the ASHRAE Standard 62-1989, the minimum outdoor air requirements are 20 CFM/person in an office environment. Manufacturing environments would require more outdoor air, depending on the chemicals used and local ventilation requirements. 20 CFM is independent of room size and is based on 7 people per 1000 square feet of floor space.
Worker draft complaints, impairment of local exhaust, difficulty opening doors, and a general reduction in mechanical ventilation are examples of:
A) Insufficient make up air systems
B) Cross drafts
C) Short circuiting
D) Insufficient capture velocity
The correct answer is: A
Adequate amounts of make up air must be provided to balance that air removed by operation of local exhaust systems, otherwise the work area will be under relatively negative pressure and the listed conditions will begin to appear.
In calculating the amount of makeup air required, the critical criterion is the:
A) Number of air changes
B) Toxicity of materials used in the workspace
C) Volume of air exhausted
D) Temperature
The correct answer is: C
The purpose of makeup air is to replace the air removed by exhaust ventilation. Therefore, the volume of air exhausted should equal the amount of makeup air. The temperature, toxicity of materials, and number of air changes affect the amount of air exhausted, which then affects the makeup air required.
A room ventilation system has been designed to provide 5 CFM of outdoor air/person. Which statement best describes the situation?
A) The ventilation rate would be insufficient for most environments
B) The ventilation rate is sufficient for offices only
C) The room must be at least 10,000 square feet
D) The room cannot be occupied by more than 7 people
The correct answer is: A
According to the ASHRAE Standard 62-1989, the minimum outdoor air requirements are 20 CFM/person in an office environment. Manufacturing environments would require more outdoor air, depending on the chemicals used and local ventilation requirements. 20 CFM is independent of room size and is based on 7 people per 1000 square feet of floor space.
Worker draft complaints, impairment of local exhaust, difficulty opening doors, and a general reduction in mechanical ventilation are examples of:
A) Insufficient make up air systems
B) Cross drafts
C) Short circuiting
D) Insufficient capture velocity
The correct answer is: A
Adequate amounts of make up air must be provided to balance that air removed by operation of local exhaust systems, otherwise the work area will be under relatively negative pressure and the listed conditions will begin to appear.
In calculating the amount of makeup air required, the critical criterion is the:
A) Number of air changes
B) Toxicity of materials used in the workspace
C) Volume of air exhausted
D) Temperature
The correct answer is: C
The purpose of makeup air is to replace the air removed by exhaust ventilation. Therefore, the volume of air exhausted should equal the amount of makeup air. The temperature, toxicity of materials, and number of air changes affect the amount of air exhausted, which then affects the makeup air required.
17. Make-Up Air Systems Reasons for designing and providing dedicated make-up air systems
Avoid high-velocity drafts through cracks in walls, under doors, and through windows
Avoid differential pressures on doors, exits, and windows
Provide an opportunity to temper the replacement air
If make-up air is not provided, a slight negative pressure will be created in the room and air flow through the exhaust system will be reduced
MAKE-UP AIR SYSTIS Exhaust ventilation systems require the replacement of exhausted air. Replacement air is often called make-up air. Replacement air can be supplied naturally by atmospheric pressure through open doors, windows, wall louvers, and adjacent spaces (acceptable), as well as through cracks in walls and windows, beneath doors, and through roof vents (unacceptable). Make-up air can also be provided through dedicated replacement air systems. Generally, exhaust systems are interlocked with a dedicated make-up air system. Other reasons for designing and providing dedicated make-up air systems are that they:
Avoid high-velocity drafts through cracks in walls, under doors, and through windows;
Avoid differential pressures on doors, exits, and windows; and
Provide an opportunity to temper the replacement air.
If make-up air is not provided, a slight negative pressure will be created in the room and air flow through the exhaust system will be reduced.
When designing exhaust ventilation, one should:
A) Also ensure adequate supply of make up air
B) Add 50% capacity to handle infiltration
C) Not be concerned with the type of contaminant
D) Oversize the fan 50% to achieve more efficiency
The correct answer is: A
It is imperative when designing the exhaust ventilation that the make-up air is also designed in. If make-up air is not adequate the exhaust system will probably not function properly. In addition, drafts and difficulty opening doors will probably occur.
Which factor is the least critical consideration for hazard or nuisance controlled by dilution ventilation:
A) Quantity of contaminant generated
B) Worker's position
C) Toxicity of contaminant
D) Duration of operation
The correct answer is: D
It is important to investigate the toxicity of the material, the position of the worker, and the quantity of contaminant being generated before dilution ventilation is used to protect the worker. Duration of the exposure is the least critical consideration.MAKE-UP AIR SYSTIS Exhaust ventilation systems require the replacement of exhausted air. Replacement air is often called make-up air. Replacement air can be supplied naturally by atmospheric pressure through open doors, windows, wall louvers, and adjacent spaces (acceptable), as well as through cracks in walls and windows, beneath doors, and through roof vents (unacceptable). Make-up air can also be provided through dedicated replacement air systems. Generally, exhaust systems are interlocked with a dedicated make-up air system. Other reasons for designing and providing dedicated make-up air systems are that they:
Avoid high-velocity drafts through cracks in walls, under doors, and through windows;
Avoid differential pressures on doors, exits, and windows; and
Provide an opportunity to temper the replacement air.
If make-up air is not provided, a slight negative pressure will be created in the room and air flow through the exhaust system will be reduced.
When designing exhaust ventilation, one should:
A) Also ensure adequate supply of make up air
B) Add 50% capacity to handle infiltration
C) Not be concerned with the type of contaminant
D) Oversize the fan 50% to achieve more efficiency
The correct answer is: A
It is imperative when designing the exhaust ventilation that the make-up air is also designed in. If make-up air is not adequate the exhaust system will probably not function properly. In addition, drafts and difficulty opening doors will probably occur.
Which factor is the least critical consideration for hazard or nuisance controlled by dilution ventilation:
A) Quantity of contaminant generated
B) Worker's position
C) Toxicity of contaminant
D) Duration of operation
The correct answer is: D
It is important to investigate the toxicity of the material, the position of the worker, and the quantity of contaminant being generated before dilution ventilation is used to protect the worker. Duration of the exposure is the least critical consideration.
18. Requirements For Recirculation of Exhaust Air Can not recirculate exhaust air when substance poses a health hazard to employees or is flammable
19. Pressure Take a straw and put into a glass of water just holding the straw there
In the straw the water will just go to the level in the bottle
Pressure in the straw air = atmospheric pressure
One atmosphere (1 atm)
14.7 pounds per square inch
407 inches of water
760 mm of mercury
20. Pressure Start sucking on the straw and water rises up the straw
Pressure in the straw is less than atmospheric pressure so the weight pushing down on the water pushes the water up the straw
21. A tire stays expanded because the pressure inside the tire is greater than the pressure of the air pushing against the tire
Greater than the air outside
Air inside the tire is
pushing in all
directions
perpendicular
to all parts of
the tire
Static pressure
22. Put a hole in the tire so the air starts to move out
Air still inside the tire is pressing against the surface of the tire that is greater than the pressure outside the tire
Air starts to move outside of the tire due to the pressure difference
Pressure higher inside the tire vs. pressure outside the tire
Velocity pressure
Velocity pressure will
eventually go to
zero when the static
pressure inside the
tire is the same as the
pressure outside of the tire HEAD Pressure, e.g. "The head is 1 in w.g."
HOOD A device that encloses, captures, or receives emitted contaminants.
HOOD ENTRY LOSS (He) The static pressure lost (in inches of water) when air enters a duct through a hood. The majority of the loss usually is associated with a vena contracta formed in the duct.
HOOD STATIC PRESSURE (SPh) The sum of the duct velocity pressure and the hood entry loss; hood static pressure is the static pressure required to accelerate air at rest outside the hood into the duct at velocity.
HVAC (HEATING, VENTILATION, AND AIR CONDITIONING) SYSTIS Ventilating systems designed primarily to control temperature, humidity, odors, and air quality.
INDOOR AIR QUALITY (IAQ), SICK-BUILDING SYNDROME, TIGHT-BUILDING SYNDROME The study, examination, and control of air quality related to temperature, humidity, and airborne contaminants.
n. w.g. (inches of water) A unit of pressure. One inch of water is equal to 0.0735 in. of mercury, or 0.036 psi. Atmospheric pressure at standard conditions is 407 in. w.g.
INDUSTRIAL VENTILATION (IV) The equipment or operation associated with the supply or exhaust of air by natural or mechanical means to control occupational hazards in the industrial setting.
LAMINAR FLOW (also Streamline Flow) Air flow in which air molecules travel parallel to all other molecules; laminar flow is characterized by the absence of turbulence.
LOCAL EXHAUST VENTILATION An industrial ventilation system that captures and removes emitted contaminants before dilution into the ambient air of the workplace.
LOSS Usually refers to the conversion of static pressure to heat in components of the ventilation system, e.g., "the hood entry loss.“
MAKE-UP AIR See Replacement and Compensating Air.
HEAD Pressure, e.g. "The head is 1 in w.g."
HOOD A device that encloses, captures, or receives emitted contaminants.
HOOD ENTRY LOSS (He) The static pressure lost (in inches of water) when air enters a duct through a hood. The majority of the loss usually is associated with a vena contracta formed in the duct.
HOOD STATIC PRESSURE (SPh) The sum of the duct velocity pressure and the hood entry loss; hood static pressure is the static pressure required to accelerate air at rest outside the hood into the duct at velocity.
HVAC (HEATING, VENTILATION, AND AIR CONDITIONING) SYSTIS Ventilating systems designed primarily to control temperature, humidity, odors, and air quality.
INDOOR AIR QUALITY (IAQ), SICK-BUILDING SYNDROME, TIGHT-BUILDING SYNDROME The study, examination, and control of air quality related to temperature, humidity, and airborne contaminants.
n. w.g. (inches of water) A unit of pressure. One inch of water is equal to 0.0735 in. of mercury, or 0.036 psi. Atmospheric pressure at standard conditions is 407 in. w.g.
INDUSTRIAL VENTILATION (IV) The equipment or operation associated with the supply or exhaust of air by natural or mechanical means to control occupational hazards in the industrial setting.
LAMINAR FLOW (also Streamline Flow) Air flow in which air molecules travel parallel to all other molecules; laminar flow is characterized by the absence of turbulence.
LOCAL EXHAUST VENTILATION An industrial ventilation system that captures and removes emitted contaminants before dilution into the ambient air of the workplace.
LOSS Usually refers to the conversion of static pressure to heat in components of the ventilation system, e.g., "the hood entry loss.“
MAKE-UP AIR See Replacement and Compensating Air.
23. Pressure Static Pressure
Pressure the air exerts by virtue of its mass in every direction perpendicular to any surface that it presses against
SP (?)
Before fan (-)
After fan(+)
Velocity Pressure
Pressure created by air because of its motion
VP (always +)
Air likes to move from high pressure to low pressure
Total Pressure
Equal to static pressure
plus velocity pressure
TP = VP + SP
TP (?)
Static pressure in a ventilation system can NOT be measured with a:
A) U tube manometer
B) Velometer
C) Magnehelic gauge
D) Inclined manameter
The correct answer is: B
With the exception of the velometer (which measures air flow rates), the other devices listed may be utilized to measure static pressure in a ventilation system.
Which of the following statements is not true about the static pressure in a given ventilation system?
A) It is measured parallel to the direction of flow
B) It tends to collapse the duct in an exhaust system
C) It acts in all directions
D) It is available to do work
The correct answer is: A
The static pressure is always measured perpendicular to the direction of flow.
Velocity pressure is:
A) The velocity of air divided by 4005 (square root of the SP)
B) The difference between total pressure and static pressure
C) Independent of velocity
D) Proportional to the square root of velocity
The correct answer is: B
The total pressure in a ventilation system is equal to the static pressure plus the velocity pressure. The velocity pressure, therefore, is the difference between the total pressure and the static pressure. The CFM is equal to the area of the duct multiplied by 4005 (square root of the velocity pressure). The velocity pressure is directly related to the square of velocity of air in the duct.
Static pressure in a ventilation system can NOT be measured with a:
A) U tube manometer
B) Velometer
C) Magnehelic gauge
D) Inclined manameter
The correct answer is: B
With the exception of the velometer (which measures air flow rates), the other devices listed may be utilized to measure static pressure in a ventilation system.
Which of the following statements is not true about the static pressure in a given ventilation system?
A) It is measured parallel to the direction of flow
B) It tends to collapse the duct in an exhaust system
C) It acts in all directions
D) It is available to do work
The correct answer is: A
The static pressure is always measured perpendicular to the direction of flow.
Velocity pressure is:
A) The velocity of air divided by 4005 (square root of the SP)
B) The difference between total pressure and static pressure
C) Independent of velocity
D) Proportional to the square root of velocity
The correct answer is: B
The total pressure in a ventilation system is equal to the static pressure plus the velocity pressure. The velocity pressure, therefore, is the difference between the total pressure and the static pressure. The CFM is equal to the area of the duct multiplied by 4005 (square root of the velocity pressure). The velocity pressure is directly related to the square of velocity of air in the duct.
24. Basic assumptions Air flow in exhaust systems
Air is considered an incompressible fluid
Air flow inside ducting will always be in the turbulent region
Heat transfer effects are neglected
The air is assumed to be dry
The weight and
volume of contaminant
in air stream are ignored
for usual designs
Nature of fluid flow
Reynolds Number
What is the density of dry air in units of lbs/ft3 at 70° F, the industrial ventilation design standard?
A) 0.075 lb/ft3
B) 0.15 lb/ft3
C) 1.0 lb/ft3
D) 1.5 lb/ft3
The correct answer is: A
Density air = Pressure air * Mass air / RT air
= 17.7 psi * 28.96 lb/lb mole * 144 in2 /1544 lbf/lb mole * 529.6 R
= 0.074959 lb/ft3
In industrial ventilation system design, which of the following assumptions is false?
A) Air is considered a compressible fluid
B) Air flow requirements should be minimized
C) Energy should be conserved
D) The worker's breathing zone must be protected
The correct answer is: A
Air is considered an incompressible fluid. This assumption allows various laws to be applied which otherwise could not be used to estimate air flows, velocities, etc..What is the density of dry air in units of lbs/ft3 at 70° F, the industrial ventilation design standard?
A) 0.075 lb/ft3
B) 0.15 lb/ft3
C) 1.0 lb/ft3
D) 1.5 lb/ft3
The correct answer is: A
Density air = Pressure air * Mass air / RT air
= 17.7 psi * 28.96 lb/lb mole * 144 in2 /1544 lbf/lb mole * 529.6 R
= 0.074959 lb/ft3
In industrial ventilation system design, which of the following assumptions is false?
A) Air is considered a compressible fluid
B) Air flow requirements should be minimized
C) Energy should be conserved
D) The worker's breathing zone must be protected
The correct answer is: A
Air is considered an incompressible fluid. This assumption allows various laws to be applied which otherwise could not be used to estimate air flows, velocities, etc..
25. Local Exhaust System Fan off
Static pressure on the duct is one atmospheric pressure, inside
the duct is also one atmosphere Methods to control Legionnaires Disease include the following except:
A) Continuous feed biocide
B) Locate make-up air intakes upwind from cooling towers
C) Periodic cleaning of cooling water systems
D) Sampling to ensure bacterial control
The correct answer is: A
Continuous feed biocides can cause resistant strains of bacteria in the cooling system. It is best to alternate biocides to prevent resistance. Prevention of cooling tower aerosols into the building make-up air will prevent bacteria from entering the ventilation system. Complete periodic cleaning and sampling of the cooling water systems have proven effective.
Which of the following sources of indoor air pollution in an office environment can be lethal?
A) Microorganisms
B) Formaldehyde
C) Carbon dioxide
D) Poor ventilation
The correct answer is: A
Airborne microorganisms circulated from water-cooling systems (Legionella Pneumophila) have caused Legionnaires Disease from acute exposures. Formaldehyde and carbon dioxide require concentrations well beyond those found in offices to be lethal. Poor ventilation would require reductions in oxygen level below 19.5%, which is unlikely in an office environment.
Methods to control Legionnaires Disease include the following except:
A) Continuous feed biocide
B) Locate make-up air intakes upwind from cooling towers
C) Periodic cleaning of cooling water systems
D) Sampling to ensure bacterial control
The correct answer is: A
Continuous feed biocides can cause resistant strains of bacteria in the cooling system. It is best to alternate biocides to prevent resistance. Prevention of cooling tower aerosols into the building make-up air will prevent bacteria from entering the ventilation system. Complete periodic cleaning and sampling of the cooling water systems have proven effective.
Which of the following sources of indoor air pollution in an office environment can be lethal?
A) Microorganisms
B) Formaldehyde
C) Carbon dioxide
D) Poor ventilation
The correct answer is: A
Airborne microorganisms circulated from water-cooling systems (Legionella Pneumophila) have caused Legionnaires Disease from acute exposures. Formaldehyde and carbon dioxide require concentrations well beyond those found in offices to be lethal. Poor ventilation would require reductions in oxygen level below 19.5%, which is unlikely in an office environment.
26. Fan on
Still has static pressure inside the fan
The static pressure inside the fan is less than the static pressure outside because air moves from a higher pressure to a lower pressure
There has to be negative pressure to move air into the duct
Static Pressure down from the fan is greater than the static pressure outside because you’re moving air into the outside
27. Local Exhaust System SP = -
VP = +
TP = - Static pressure upstream from the fan inside the duct is negative.
Total pressure on the upstream side is negative
Static pressure downstream from the fan inside the duct is positive while total pressure is positive
Velocity pressure is always positiveStatic pressure upstream from the fan inside the duct is negative.
Total pressure on the upstream side is negative
Static pressure downstream from the fan inside the duct is positive while total pressure is positive
Velocity pressure is always positive
28. Volumetric Flow Rate The amount of air going through a system at a certain point
Q
Given in Cubic Feet Per Minute (CFM)
The amount of air flowing through any point has to be the same
Volume of air has to be the same, but the area and the velocity do no remain the same
If you increase the area you decrease the velocity
29. Basic Definitions Velocity
Flow rate of air through duct
V(fpm)
Velocity = 4005 x Square Root of Velocity Pressure
V = 4005 ?VP
Area
Area of duct
A(ft˛)
Volumetric Flow Rate = Velocity x Area
Q(cfm or ft3/min)=VA acfm Actual cubic feet per minute of gas flowing at existing temperature and pressure. (See also scfm.)
ACH, AC/H (air changes per hour) The number of times air is replaced in an hour.
AIR DENSITY The weight of air in lbs per cubic foot. Dry standard air at T=68° F (20° C) and BP = 29.92 in Hg (760 mm Hg) has a density of 0.075 lb/cu ft.
ANIOMETER A device that measures the velocity of air. Common types include the swinging vane and the hot-wire anemometer.
AREA (A) The cross-sectional area through which air moves. Area may refer to the cross-sectional area of a duct, a window, a door, or any space through which air moves.
ATMOSPHERIC PRESSURE The pressure exerted in all directions by the atmosphere. At sea level, mean atmospheric pressure is 29.92 in Hg, 14.7 psi, 407 in w.g., or 760 mm Hg.
BRAKE HORSEPOWER (bhp) The actual horsepower required to move air through a ventilation system against a fixed total pressure plus the losses in the fan. bhp=ahp × 1/eff, where eff is fan mechanical efficiency.
BRANCH In a junction of two ducts, the branch is the duct with the lowest volume flow rate. The branch usually enters the main at an angle of less than 90.
CANOPY HOOD (Receiving Hood) A one- or two-sided overhead hood that receives rising hot air or gas.
CAPTURE VELOCITY The velocity of air induced by a hood to capture emitted contaminants external to the hood.
COEFFICIENT OF ENTRY (Ce) A measure of the efficiency of a hood's ability to convert static pressure to velocity pressure; the ratio of actual flow to ideal flow.
DENSITY CORRECTION FACTOR A factor applied to correct or convert dry air density of any temperature to velocity pressure; the ratio of actual flow to ideal flow.
DILUTION VENTILATION (General Exhaust Ventilation) A form of exposure control that involves providing enough air in the workplace to dilute the concentration of airborne contaminants to acceptable levels.
ENTRY LOSS See Hood Entry Loss or Branch Entry Loss.
EVASE (pronounced eh-va-say) A cone-shaped exhaust stack that recaptures static pressure from velocity pressure.
FAN A mechanical device that moves air and creates static pressure.
FAN LAWS Relationships that describe theoretical, mutual performance changes in pressure, flow rate, rpm of the fan, horsepower, density of air, fan size, and sound power.
FAN CURVE A curve relating pressure and volume flow rate of a given fan at a fixed fan speed (rpm).
FRICTION LOSS The static pressure loss in a system caused by friction between moving air and the duct wall, expressed as in w.g./100 ft, or fractions of VP per 100 ft of duct (mm w.g./m; Kpa/m).
GAUGE PRESSURE The difference between two absolute pressures, one of which is usually atmospheric pressure.
GENERAL EXHAUST See Dilution Ventilation.acfm Actual cubic feet per minute of gas flowing at existing temperature and pressure. (See also scfm.)
ACH, AC/H (air changes per hour) The number of times air is replaced in an hour.
AIR DENSITY The weight of air in lbs per cubic foot. Dry standard air at T=68° F (20° C) and BP = 29.92 in Hg (760 mm Hg) has a density of 0.075 lb/cu ft.
ANIOMETER A device that measures the velocity of air. Common types include the swinging vane and the hot-wire anemometer.
AREA (A) The cross-sectional area through which air moves. Area may refer to the cross-sectional area of a duct, a window, a door, or any space through which air moves.
ATMOSPHERIC PRESSURE The pressure exerted in all directions by the atmosphere. At sea level, mean atmospheric pressure is 29.92 in Hg, 14.7 psi, 407 in w.g., or 760 mm Hg.
BRAKE HORSEPOWER (bhp) The actual horsepower required to move air through a ventilation system against a fixed total pressure plus the losses in the fan. bhp=ahp × 1/eff, where eff is fan mechanical efficiency.
BRANCH In a junction of two ducts, the branch is the duct with the lowest volume flow rate. The branch usually enters the main at an angle of less than 90.
CANOPY HOOD (Receiving Hood) A one- or two-sided overhead hood that receives rising hot air or gas.
CAPTURE VELOCITY The velocity of air induced by a hood to capture emitted contaminants external to the hood.
COEFFICIENT OF ENTRY (Ce) A measure of the efficiency of a hood's ability to convert static pressure to velocity pressure; the ratio of actual flow to ideal flow.
DENSITY CORRECTION FACTOR A factor applied to correct or convert dry air density of any temperature to velocity pressure; the ratio of actual flow to ideal flow.
DILUTION VENTILATION (General Exhaust Ventilation) A form of exposure control that involves providing enough air in the workplace to dilute the concentration of airborne contaminants to acceptable levels.
ENTRY LOSS See Hood Entry Loss or Branch Entry Loss.
EVASE (pronounced eh-va-say) A cone-shaped exhaust stack that recaptures static pressure from velocity pressure.
FAN A mechanical device that moves air and creates static pressure.
FAN LAWS Relationships that describe theoretical, mutual performance changes in pressure, flow rate, rpm of the fan, horsepower, density of air, fan size, and sound power.
FAN CURVE A curve relating pressure and volume flow rate of a given fan at a fixed fan speed (rpm).
FRICTION LOSS The static pressure loss in a system caused by friction between moving air and the duct wall, expressed as in w.g./100 ft, or fractions of VP per 100 ft of duct (mm w.g./m; Kpa/m).
GAUGE PRESSURE The difference between two absolute pressures, one of which is usually atmospheric pressure.
GENERAL EXHAUST See Dilution Ventilation.
30. Air Flow Face Velocity
Velocity if the air at the opening of the hood
31. Basic Definitions Types of Pressure Losses
Hood Entry Loss
Duct Friction Loss Duct Loss
Elbows, Contractions, Expansions
Entry Loss
Branch and Fan Entries, Cleaners MANOMETER A device that measures pressure difference; usually a U-shaped glass tube containing water or mercury.
MINIMUM TRANSPORT VELOCITY (MTV). The minimum velocity that will transport particles in a duct with little settling; MTV varies with air density, particulate loading, and other factors.
OUTDOOR AIR (OA) Outdoor air is the "fresh" air mixed with return air (RA) to dilute contaminants in the supply air.
PITOT TUBE A device used to measure total and static pressures in an airstream.
PLENUM A low-velocity chamber used to distribute static pressure throughout its interior.
PRESSURE DROP The loss of static pressure across a point; for example, "the pressure drop across an orifice is 2.0 in. w.g."
REPLACEMENT AIR (also, Compensating Air, Make-Up Air) Air supplied to a space to replace exhausted air.
RETURN AIR Air that is returned from the primary space to the fan for recirculation.
scfm Standard cubic feet per minute. A measure of air flow at standard conditions, i.e., dry air at 29.92 in. Hg (760 mm Hg) (gauge), 68° F (20° C).
SLOT VELOCITY The average velocity of air through a slot. Slot velocity is calculated by dividing the total volume flow rate by the slot area (usually, Vs = 2,000 fpm).
STACK A device on the end of a ventilation system that disperses exhaust contaminants for dilution by the atmosphere.
STANDARD AIR, STANDARD CONDITIONS Dry air at 68° F (20° C), 29.92 in Hg (760 mm Hg).
STATIC PRESSURE (SP) The pressure developed in a duct by a fan; the force in inches of water measured perpendicular to flow at the wall of the duct; the difference in pressure between atmospheric pressure and the absolute pressure inside a duct, cleaner, or other equipment; SP exerts influence in all directions.
SUCTION PRESSURE (See Static Pressure.) An archaic term that refers to static pressure on the upstream side of the fan.
TOTAL PRESSURE (TP) The pressure exerted in a duct, i.e., the sum of the static pressure and the velocity pressure; also called Impact Pressure, Dynamic Pressure.
TRANSPORT VELOCITY See Minimum Transport Velocity.
TURBULENT FLOW Air flow characterized by transverse velocity components as well as velocity in the primary direction of flow in a duct; mixing velocities.
VELOCITY (V) The time rate of movement of air; usually expressed as feet per minute.
VELOCITY PRESSURE (VP) The pressure attributed to the velocity of air.
VOLUME FLOW RATE (Q) Quantity of air flow in cfm, scfm, or acfm. MANOMETER A device that measures pressure difference; usually a U-shaped glass tube containing water or mercury.
MINIMUM TRANSPORT VELOCITY (MTV). The minimum velocity that will transport particles in a duct with little settling; MTV varies with air density, particulate loading, and other factors.
OUTDOOR AIR (OA) Outdoor air is the "fresh" air mixed with return air (RA) to dilute contaminants in the supply air.
PITOT TUBE A device used to measure total and static pressures in an airstream.
PLENUM A low-velocity chamber used to distribute static pressure throughout its interior.
PRESSURE DROP The loss of static pressure across a point; for example, "the pressure drop across an orifice is 2.0 in. w.g."
REPLACEMENT AIR (also, Compensating Air, Make-Up Air) Air supplied to a space to replace exhausted air.
RETURN AIR Air that is returned from the primary space to the fan for recirculation.
scfm Standard cubic feet per minute. A measure of air flow at standard conditions, i.e., dry air at 29.92 in. Hg (760 mm Hg) (gauge), 68° F (20° C).
SLOT VELOCITY The average velocity of air through a slot. Slot velocity is calculated by dividing the total volume flow rate by the slot area (usually, Vs = 2,000 fpm).
STACK A device on the end of a ventilation system that disperses exhaust contaminants for dilution by the atmosphere.
STANDARD AIR, STANDARD CONDITIONS Dry air at 68° F (20° C), 29.92 in Hg (760 mm Hg).
STATIC PRESSURE (SP) The pressure developed in a duct by a fan; the force in inches of water measured perpendicular to flow at the wall of the duct; the difference in pressure between atmospheric pressure and the absolute pressure inside a duct, cleaner, or other equipment; SP exerts influence in all directions.
SUCTION PRESSURE (See Static Pressure.) An archaic term that refers to static pressure on the upstream side of the fan.
TOTAL PRESSURE (TP) The pressure exerted in a duct, i.e., the sum of the static pressure and the velocity pressure; also called Impact Pressure, Dynamic Pressure.
TRANSPORT VELOCITY See Minimum Transport Velocity.
TURBULENT FLOW Air flow characterized by transverse velocity components as well as velocity in the primary direction of flow in a duct; mixing velocities.
VELOCITY (V) The time rate of movement of air; usually expressed as feet per minute.
VELOCITY PRESSURE (VP) The pressure attributed to the velocity of air.
VOLUME FLOW RATE (Q) Quantity of air flow in cfm, scfm, or acfm.
32. Hoods Covers the process to the extent possible
Critical Elements
Geometry of the hood
Location of the hood relative to the generation of the contaminant
Amount of air being pulled through the hood
33. Hoods Design Rules
Enclose as much of the process as possible
Always try to enclose as much as possible
Get the hood as close as possible to the source of contaminant generation
The closer the hood is the greater the ability to reduce competing air currents
Calculate required capture velocity
Need to have enough air flow to overcome opposing air currents to have the ability to pick up the contaminant and take it away into the ventilation system
What pressure is required
to capture the contaminant,
bring it into the hood, move it
through the ducts, into the fan
and out of the exhaust, through
the air cleaner and out
of the stack
34. Hoods The purpose of most ventilation systems is to prevent worker inhalation of contaminants
For this reason, the hood should be located
so that contaminants are not drawn
through the worker's breathing zone
This is especially important where workers
lean over an operation such as an
open-surface tank or welding bench When using a capture or receiving hood, the hood should be located as close to the contaminant source as possible. Reducing the amount of contaminants generated or released from the process reduces ventilation requirements.
The hood should be designed to achieve good air distribution into the hood openings so that all the air drawn into the hood helps to control contaminants. Avoid designs that require that the velocities through some openings be very high in order to develop the minimum acceptable velocity through other openings or parts of the hood.
The purpose of most ventilation systems is to prevent worker inhalation of contaminants. For this reason, the hood should be located so that contaminants are not drawn through the worker's breathing zone. This is especially important where workers lean over an operation such as an open-surface tank or welding bench.
Hoods must meet the design criteria in the ACGIH Industrial Ventilation Manual or applicable OSHA standards. Most hood design recommendations account for cross-drafts that interfere with hood operation. Strong cross-drafts can easily reduce a hood's effectiveness by 75%. Standard hood designs may not be adequate to contain highly toxic materials.
The hood should be designed to cause minimum interference with the performance of work. Positioning access doors inside an enclosure that must be opened and closed often means that in practice the doors will be left open, and locating capture hoods too close to the process for the worker's convenience often means that the hood will be disassembled and removed. Hoods should never increase the likelihood of mechanical injury by interfering with a worker's freedom to move around machinery.
When using a capture or receiving hood, the hood should be located as close to the contaminant source as possible. Reducing the amount of contaminants generated or released from the process reduces ventilation requirements.
The hood should be designed to achieve good air distribution into the hood openings so that all the air drawn into the hood helps to control contaminants. Avoid designs that require that the velocities through some openings be very high in order to develop the minimum acceptable velocity through other openings or parts of the hood.
The purpose of most ventilation systems is to prevent worker inhalation of contaminants. For this reason, the hood should be located so that contaminants are not drawn through the worker's breathing zone. This is especially important where workers lean over an operation such as an open-surface tank or welding bench.
Hoods must meet the design criteria in the ACGIH Industrial Ventilation Manual or applicable OSHA standards. Most hood design recommendations account for cross-drafts that interfere with hood operation. Strong cross-drafts can easily reduce a hood's effectiveness by 75%. Standard hood designs may not be adequate to contain highly toxic materials.
The hood should be designed to cause minimum interference with the performance of work. Positioning access doors inside an enclosure that must be opened and closed often means that in practice the doors will be left open, and locating capture hoods too close to the process for the worker's convenience often means that the hood will be disassembled and removed. Hoods should never increase the likelihood of mechanical injury by interfering with a worker's freedom to move around machinery.
35. Common Misconceptions Hoods draw air from a significant distance away from the hood opening, and therefore they can control contaminants released some distance away
Hoods must be close to the source of contamination to be effective
Heavier-than-air vapors tend to settle to the workroom floor and therefore can be collected by a hood located there
A small amount of contaminant
in the air has a resulting density
close to that of air, and random
air currents will disperse
the material throughout the room
Hoods draw air from a significant distance away from the hood opening, and therefore they can control contaminants released some distance away. It is easy to confuse a fan's ability to blow a jet of air with its ability to draw air into a hood. Hoods must be close to the source of contamination to be effective.
Heavier-than-air vapors tend to settle to the workroom floor and therefore can be collected by a hood located there. A small amount of contaminant in the air (1,000 ppm means 1,000 parts of contaminant plus 999,000 parts of air) has a resulting density close to that of air, and random air currents will disperse the material throughout the room.
Of the following methods of controlling exposure to airborne contaminants, which is generally thought to be most preferred and thus should be tried first?
A) Local exhaust ventilation to control exposure to the contaminants at the source
B) Substitution or process modification to reduce the generation of the contaminants
C) General exhaust ventilation to reduce the airborne contaminant concentration to an acceptable level
D) Administrative controls to ensure that worker exposure is always below the PEL
The correct answer is: B
Engineering control to reduce contaminant generation at the source is generally regarded as the best way to control worker exposure to airborne contaminants, since it is a permanent change to the process which prevents the contaminants from becoming airborne.
In virtually all ventilation systems, air flow is:
A) Laminar
B) Turbulent
C) Supersonic
D) Frictionless
The correct answer is: B
The Reynolds number required for fully turbulent flow, 4000, is easily exceeded in almost all ventilation systems.
Hoods draw air from a significant distance away from the hood opening, and therefore they can control contaminants released some distance away. It is easy to confuse a fan's ability to blow a jet of air with its ability to draw air into a hood. Hoods must be close to the source of contamination to be effective.
Heavier-than-air vapors tend to settle to the workroom floor and therefore can be collected by a hood located there. A small amount of contaminant in the air (1,000 ppm means 1,000 parts of contaminant plus 999,000 parts of air) has a resulting density close to that of air, and random air currents will disperse the material throughout the room.
Of the following methods of controlling exposure to airborne contaminants, which is generally thought to be most preferred and thus should be tried first?
A) Local exhaust ventilation to control exposure to the contaminants at the source
B) Substitution or process modification to reduce the generation of the contaminants
C) General exhaust ventilation to reduce the airborne contaminant concentration to an acceptable level
D) Administrative controls to ensure that worker exposure is always below the PEL
The correct answer is: B
Engineering control to reduce contaminant generation at the source is generally regarded as the best way to control worker exposure to airborne contaminants, since it is a permanent change to the process which prevents the contaminants from becoming airborne.
In virtually all ventilation systems, air flow is:
A) Laminar
B) Turbulent
C) Supersonic
D) Frictionless
The correct answer is: B
The Reynolds number required for fully turbulent flow, 4000, is easily exceeded in almost all ventilation systems.
36. Types of Hoods Key to classification is the location of the hood relative to where the contaminant is generated
Enclosing Hood
Exterior Hood
Receiving Hood
For local exhaust ventilation of an electroplating tank, the preferable type of hood is:
A) Slot
B) Canopy
C) Enclosing
D) Down draft
The correct answer is: A
Slot ventilation is the preferred method of ventilation in electroplating operations. It is the most effective means of preventing excessive amounts of air contaminants from reaching employees.
Low volume-high velocity exhaust systems utilize hood slot velocities in what range?
A) 40 - 100 ft/min
B) 800 - 3000 ft/min
C) 5,000 - 9000 ft/min
D) 24,000 - 39,000 ft/min
The correct answer is: D
These hoods use extremely high velocities, as shown by Answer D.
NOTE: Earlier editions of the Ventilation Manual give a range of 10,000 - 25,000 ft/min.For local exhaust ventilation of an electroplating tank, the preferable type of hood is:
A) Slot
B) Canopy
C) Enclosing
D) Down draft
The correct answer is: A
Slot ventilation is the preferred method of ventilation in electroplating operations. It is the most effective means of preventing excessive amounts of air contaminants from reaching employees.
Low volume-high velocity exhaust systems utilize hood slot velocities in what range?
A) 40 - 100 ft/min
B) 800 - 3000 ft/min
C) 5,000 - 9000 ft/min
D) 24,000 - 39,000 ft/min
The correct answer is: D
These hoods use extremely high velocities, as shown by Answer D.
NOTE: Earlier editions of the Ventilation Manual give a range of 10,000 - 25,000 ft/min.
37. Enclosure Hoods Totally enclosed
Glove box
Hood open
on one side
Tunnel
Hood open
on each end
38. Exterior Hoods Contaminants are generated outside of the hood
Very common
Types
Welding hood
Elephant trunk
39. Receiving Hoods Hood catches whatever is coming at the hood due to
Momentum of the particles
Heat imparted to gases or vapors
Take advantage of the process
Close to the process
Examples:
grinding hood
Canopy hood
40. Canopy Hoods Design Considerations
Are vapors actually going to rise?
Other sources of air movement
You want still air
Cannot have this type of hood in a drafty room
Is a worker leaning over the process? Can see a canopy hood in a place that sterilizes things
A closed room that has ethylene oxide in it
After letting things sit in the room that need to be sterilized, a canopy hood is used to suck out the ethylene oxide (a very large canopy hood)Can see a canopy hood in a place that sterilizes things
A closed room that has ethylene oxide in it
After letting things sit in the room that need to be sterilized, a canopy hood is used to suck out the ethylene oxide (a very large canopy hood)
41. Fan Selection Information which must be known
Air volume to be moved
Fan static pressure
Type and concentration of contaminants in the air
Because this affects the fan type and materials of construction
Noise is a limiting factor
FAN SELECTION To choose the proper fan for a ventilation system, this information must be known:
air volume to be moved;
fan static pressure;
type and concentration of contaminants in the air (because this affects the fan type and materials of construction); and
the importance of noise as a limiting factor.
Once this information is available, the type of fan best suited for the system can be chosen. Many different fans are available, although they all fall into one of two classes: axial flow fans and centrifugal fans. For a detailed explanation of fans, see the ACGIH Industrial Ventilation Manual.
Which of the following applications would be suitable for a forward-curved blade centrifugal fan?
A) Exhausting a pedestal grinder
B) Exhausting a oven drying operation
C) Providing room air conditioning through a unit ventilator
D) As a wall fan, providing general exhaust ventilation
Answers A and B are both local exhaust systems, and forward-curved blade fans cannot develop sufficient static pressure for such applications. Centrifugal fans are not generally used as wall fans, eliminating Answer D.
Which of the following fan types is most commonly used in a general exhaust ventilation system?
A) Backward-curved blade centrifugal fan
B) Propeller-type axial fan
C) Vane-axial fan
D) Radial-blade centrifugal fan
The correct answer is: B
The propeller-type axial fan cannot be used in a duct system. It is best suited for use in a general exhaust ventilation system.
A portable exhaust ventilation system operates at different altitudes throughout the country. Which of the following quantities is constant at every location?
A) Mass flow rate
B) Volumetric flow rate
C) Air density
D) Absolute pressure
The correct answer is: B
A fan attached to a certain system will maintain a constant volumetric flow rate; the mass flow rate will vary with the air density, which changes with altitude.FAN SELECTION To choose the proper fan for a ventilation system, this information must be known:
air volume to be moved;
fan static pressure;
type and concentration of contaminants in the air (because this affects the fan type and materials of construction); and
the importance of noise as a limiting factor.
Once this information is available, the type of fan best suited for the system can be chosen. Many different fans are available, although they all fall into one of two classes: axial flow fans and centrifugal fans. For a detailed explanation of fans, see the ACGIH Industrial Ventilation Manual.
Which of the following applications would be suitable for a forward-curved blade centrifugal fan?
A) Exhausting a pedestal grinder
B) Exhausting a oven drying operation
C) Providing room air conditioning through a unit ventilator
D) As a wall fan, providing general exhaust ventilation
Answers A and B are both local exhaust systems, and forward-curved blade fans cannot develop sufficient static pressure for such applications. Centrifugal fans are not generally used as wall fans, eliminating Answer D.
Which of the following fan types is most commonly used in a general exhaust ventilation system?
A) Backward-curved blade centrifugal fan
B) Propeller-type axial fan
C) Vane-axial fan
D) Radial-blade centrifugal fan
The correct answer is: B
The propeller-type axial fan cannot be used in a duct system. It is best suited for use in a general exhaust ventilation system.
A portable exhaust ventilation system operates at different altitudes throughout the country. Which of the following quantities is constant at every location?
A) Mass flow rate
B) Volumetric flow rate
C) Air density
D) Absolute pressure
The correct answer is: B
A fan attached to a certain system will maintain a constant volumetric flow rate; the mass flow rate will vary with the air density, which changes with altitude.
42. Ducts Air flows turbulently through ducts at between 2,000-6,000 feet per minute (fpm)
Ducts can be made of galvanized metal, fiberglass, plastic, and concrete
Friction losses vary according to ductwork type, length of duct, velocity of air, duct area, density of air, and duct diameter DUCTS Air flows turbulently through ducts at between 2,000-6,000 feet per minute (fpm). Ducts can be made of galvanized metal, fiberglass, plastic, and concrete. Friction losses vary according to ductwork type, length of duct, velocity of air, duct area, density of air, and duct diameter.
What is the recommended duct velocity for an average industrial dust such as wool, wood, sand abrasive blasting dust, or shoe dust?
A) 2000 fpm
B) 3000 fpm
C) 4000 fpm
D)5000 fpm
The correct answer is: C
4000 fpm is the value recommended by the ACGIH in the Industrial Ventilation Handbook.
A 40 inch duct requires how many points in a duct traverse?
A) 4
B) 10
C) 12
D) 16
The correct answer is: B
A 40 inch duct should have a 10 point traverse when conducting a ventilation system evaluation. A 6 point traverse should be used when ducts are less than 6 inches, and for 48 inch ducts and higher, a 20 point traverse should be used.DUCTS Air flows turbulently through ducts at between 2,000-6,000 feet per minute (fpm). Ducts can be made of galvanized metal, fiberglass, plastic, and concrete. Friction losses vary according to ductwork type, length of duct, velocity of air, duct area, density of air, and duct diameter.
What is the recommended duct velocity for an average industrial dust such as wool, wood, sand abrasive blasting dust, or shoe dust?
A) 2000 fpm
B) 3000 fpm
C) 4000 fpm
D)5000 fpm
The correct answer is: C
4000 fpm is the value recommended by the ACGIH in the Industrial Ventilation Handbook.
A 40 inch duct requires how many points in a duct traverse?
A) 4
B) 10
C) 12
D) 16
The correct answer is: B
A 40 inch duct should have a 10 point traverse when conducting a ventilation system evaluation. A 6 point traverse should be used when ducts are less than 6 inches, and for 48 inch ducts and higher, a 20 point traverse should be used.
43. Air Cleaners The design of the air cleaner depends on the degree of cleaning required
Regular maintenance of air cleaners increases their efficiency and minimizes worker exposure
Different types of air cleaners are made to remove
Particulates
Precipitators
Cyclones
Baghouses
Gases and vapors
Scrubbers AIR CLEANERS The design of the air cleaner depends on the degree of cleaning required. Regular maintenance of air cleaners increases their efficiency and minimizes worker exposure. Different types of air cleaners are made to remove particulates (e.g., precipitators, cyclones, etc.) and gases and vapors (e.g., scrubbers).
Housing designed to 20" w.g.
Continuous Pulse Jet cleaning mechanism.
10 gauge reinforced H.R. steel casting with airtight welded construction provides optimum durability designed for long lasting, trouble free operation.
Ability to handle microscopic dust particles.
Quick release access doors on clean air plenum.
Quick release access door to hopper.
Energy efficient design ensures lower operating cost.
Baffled inlet ensures quiet operation.
No tools required for installation and removal of bags and cages.
Easy inspection and maintenance access.
Factory assembled for minimum of site work.
Options
Rotary air lock.
Discharge screw conveyor.
Walkways and ladders.
Control panels.
Explosion relief panels.
Fire suppression systems.
After - filter systems.
Applications
Dust collection.
Cement Industries.
Boiler Applications.
Material Handling.
AIR CLEANERS The design of the air cleaner depends on the degree of cleaning required. Regular maintenance of air cleaners increases their efficiency and minimizes worker exposure. Different types of air cleaners are made to remove particulates (e.g., precipitators, cyclones, etc.) and gases and vapors (e.g., scrubbers).
Housing designed to 20" w.g.
Continuous Pulse Jet cleaning mechanism.
10 gauge reinforced H.R. steel casting with airtight welded construction provides optimum durability designed for long lasting, trouble free operation.
Ability to handle microscopic dust particles.
Quick release access doors on clean air plenum.
Quick release access door to hopper.
Energy efficient design ensures lower operating cost.
Baffled inlet ensures quiet operation.
No tools required for installation and removal of bags and cages.
Easy inspection and maintenance access.
Factory assembled for minimum of site work.
Options
Rotary air lock.
Discharge screw conveyor.
Walkways and ladders.
Control panels.
Explosion relief panels.
Fire suppression systems.
After - filter systems.
Applications
Dust collection.
Cement Industries.
Boiler Applications.
Material Handling.
44. Stacks They disperse exhaust air into the ambient environment
When installing stacks
Provide ample stack height
A minimum of 10 ft above adjacent rooflines or air intakes
Place stack downwind of air intakes;
Provide a stack velocity of a minimum of 1.4 times the wind velocity;
Place the stack as far from the intake as possible
50 ft is recommended
Stacks disperse exhaust air into the ambient environment. The amount of reentrainment depends on exhaust volume, wind speed and direction, temperature, location of intakes and exhausts, etc. When installing stacks:
Provide ample stack height (a minimum of 10 ft above adjacent rooflines or air intakes);
Place stack downwind of air intakes;
Provide a stack velocity of a minimum of 1.4 times the wind velocity;
Place the stack as far from the intake as possible (50 ft is recommended);
Place the stack at least 10 ft high on most roofs to avoid recirculation; and
Avoid rain caps if the air intake is within 50 ft of the stack.
Stacks disperse exhaust air into the ambient environment. The amount of reentrainment depends on exhaust volume, wind speed and direction, temperature, location of intakes and exhausts, etc. When installing stacks:
Provide ample stack height (a minimum of 10 ft above adjacent rooflines or air intakes);
Place stack downwind of air intakes;
Provide a stack velocity of a minimum of 1.4 times the wind velocity;
Place the stack as far from the intake as possible (50 ft is recommended);
Place the stack at least 10 ft high on most roofs to avoid recirculation; and
Avoid rain caps if the air intake is within 50 ft of the stack.
45. Maintenance of Ventilation System Maintenance is very important
Periodic inspection
Worker training
Maintain records
Need to be built with maintenance in mind
Ventilation systems come into contact with a lot of materials
Corrosives
Dusts
Gases
Vapors
46. Evaluation Without Instruments Perform a tissue test
Hold a tissue up and see if the system sucks it in or blows it out
Watch a worker(s) performing the process and see if the system is sucking out the contaminant
Is it dirty around the area where the process is
Where the ventilation system is
See if there are holes in the ducts
Evaluation
Lack of maintenance
Dents on the ducts
Cause a lot of loss due to friction
Is the system producing a lot of noise
Could mean a lot of energy is being wasted
47. Basic Testing Equipment Smoke tubes
Velometers, anemometers
Pressure-sensing devices
Noise-monitoring equipment
Measuring tapes
Detector tubes DOCUMENTATION. The characteristics of the ventilation system that must be documented during an investigation include equipment operability, physical measurements of the system, and use practices. EQUIPMENT OPERABILITY. Before taking velocity or pressure measurements, note and record the operating status of the equipment. For example, are filters loaded or clean? Are variable-flow devices like dampers, variable-frequency drives, or inlet vanes in use? Are make-up units operating? Are system blueprints available?
Which of the following represents a good use of an orifice meter?
A) Measurement of air flow in a calibration wind tunnel
B) Measurement of the air flows in various ducts during a ventilation survey
C) Measurement of the face velocity of a laboratory chemical hood
D) Measurement of turbulence intensity in front of an exterior exhaust hood
The correct answer is: A
Orifice meters must be built into an exhaust system and thus can only be used to measure air flow in the laboratory or other permanent installation.
The chemical component of the smoke tubes used in ventilation studies is:
A) Vanadium pentoxide
B) Titanium tetrachloride
C) Ammonium chloride
D) Dioctylphthalate
The correct answer is: B
Titanium tetrachloride decomposes in moist air to form titanium dioxide and hydrochloric acid. The titanium dioxide is white.
DOCUMENTATION. The characteristics of the ventilation system that must be documented during an investigation include equipment operability, physical measurements of the system, and use practices. EQUIPMENT OPERABILITY. Before taking velocity or pressure measurements, note and record the operating status of the equipment. For example, are filters loaded or clean? Are variable-flow devices like dampers, variable-frequency drives, or inlet vanes in use? Are make-up units operating? Are system blueprints available?
Which of the following represents a good use of an orifice meter?
A) Measurement of air flow in a calibration wind tunnel
B) Measurement of the air flows in various ducts during a ventilation survey
C) Measurement of the face velocity of a laboratory chemical hood
D) Measurement of turbulence intensity in front of an exterior exhaust hood
The correct answer is: A
Orifice meters must be built into an exhaust system and thus can only be used to measure air flow in the laboratory or other permanent installation.
The chemical component of the smoke tubes used in ventilation studies is:
A) Vanadium pentoxide
B) Titanium tetrachloride
C) Ammonium chloride
D) Dioctylphthalate
The correct answer is: B
Titanium tetrachloride decomposes in moist air to form titanium dioxide and hydrochloric acid. The titanium dioxide is white.
48. 1) Not wearing proper PPE. Eye protection, such as safety glasses or a face shield, must be worn when employee is exposed to eye hazards from flying particles. Shirt should be made of flame-retardant material.
Related information:
29 CFR 1910.133(a) Eye and Face Protection
ez Explanation™: Personal Protective Equipment
Safety Training (OSHA): Personal Protective Equipment: Eye and Face Protection
2) Sparks from grinding wheel may ignite flammable and combustible material in work area. Paint and acetylene torch should be removed. Rags should be removed from immediate work area.
Related information:
29 CFR 1910.106(e)(6) Flammable and Combustible Liquids
ez Explanation™: Fire safety
3) It is a good safety practice to secure the metal part being ground with a vice or a clamp.
4) Electrical outlet box is not used in the manner for which it is designed. Electrical equipment must be installed and used according to the instructions included in the listing or labeling.
Related information:
29 CFR 1910.303(b)(2) General Requirements
5) Standing on electrical cords. Flexible cords (extension cords) cannot be run across floors.
Related information:
29 CFR 1910.305(g)(1) Wiring methods, components, and equipment for general use
ez Explanation™: Walking-Working Surfaces
ez Explanation™: Fall Protection
1) Not wearing proper PPE. Eye protection, such as safety glasses or a face shield, must be worn when employee is exposed to eye hazards from flying particles. Shirt should be made of flame-retardant material.
Related information:
29 CFR 1910.133(a) Eye and Face Protection
ez Explanation™: Personal Protective Equipment
Safety Training (OSHA): Personal Protective Equipment: Eye and Face Protection
2) Sparks from grinding wheel may ignite flammable and combustible material in work area. Paint and acetylene torch should be removed. Rags should be removed from immediate work area.
Related information:
29 CFR 1910.106(e)(6) Flammable and Combustible Liquids
ez Explanation™: Fire safety
3) It is a good safety practice to secure the metal part being ground with a vice or a clamp.
4) Electrical outlet box is not used in the manner for which it is designed. Electrical equipment must be installed and used according to the instructions included in the listing or labeling.
Related information:
29 CFR 1910.303(b)(2) General Requirements
5) Standing on electrical cords. Flexible cords (extension cords) cannot be run across floors.
Related information:
29 CFR 1910.305(g)(1) Wiring methods, components, and equipment for general use
ez Explanation™: Walking-Working Surfaces
ez Explanation™: Fall Protection
49. VENTILATION FORMULAS Q = VA
A = ? r˛
V = 4005 ? VP
TP = SP + VP
