An Evaluation of a Workplace Hazard: Carbon Monoxide
University of Central Florida,
Introduction to Industrial Hygiene
Tim Wallace, R.S
Identification of Workplace Hazard
- Carbon Monoxide (CO) = a chemical compound consisting of one carbon and one oxygen.
- CO is a colorless and odorless gas at room temperature. Therefore, it has no WARNING properties!!!!
- The most likely route of exposure is through inhalation.
Extent of Hazard-OSHA Says:
- “Some 2,000 persons a year are killed out right by CO gas exposure”
- “At least 10,000 more workers suffer from exposure to debilitating levels of CO”
- “One of the most dangerous industrial hazards”
- “One of the most widespread”
Primarily known as an asphixiant or chemical anoxiant. This means that the CO causes absence or abnormally low amounts of oxygen in the body
CO simply disrupts the oxygen transport to all tissues in the body.
CO combines with hemoglobin in blood to form carboxyhemoglobin (COHb)
Nature of Hazard
Nature of Hazard II
- CO has an affinity for the oxygen binding site in the blood; 200 times more so than oxygen
- Other Potential Hazards (Atypical): highly flammable, may form explosive mixtures when mixed in air, may react to finely dispersed metal powders to form toxic and flammable carbonyls, may react vigorously w/ oxygen, acetylene, chlorine, fluorine, nitrous oxide.
- Other Physical Properties: BP -191ºC, MP -205°C, Explosive Limits (volume % in air) 12.5-74.2
Central Nervous System
Tissues with the highest oxygen need are first affected:
Health Effects (Target Organs or Systems)
Symptoms of Exposure
Particularly Susceptible Populations
- Pregnant Women and Young Children
- Persons with existing illnesses: WHY???
a. cardiovascular disease (heart disease, coronary artery disease)
b. pulmonary disease (asthma, emphysema, chronic bronchitis)
c. blood disorders (sickle cell anemia, lassemia, others)
Sources of CO
- Incomplete combustion of anything containing carbon (fossil fuels, wood, tobacco) - Especially high in exhaust from internal combustion engines.
- CO is a metabolic product of methylene chloride (common ingredient in paints and solvents)
- may be be produced within the body by catabolism (breakdown) of hemoglobin
Kiln and furnace operators
lawn care workers
disaster relief workers
parking garage attendants
Typical Occupations that May Experience CO Hazard
Standard Methods of Measurement/Assessment
- Direct reading CO Detector (electro-chemical voltimetric sensor) - dataloger and calibration to known gas concentration required
- sampling with calibrated vacuum pump through adsorption tube - laboratory analysis
- detector tubes certified by NIOSH
- all samples or measurements should be in the worker’s “breathing zone”
Other Methods (EPA Outside Air Methods)
- Gas Filter Correlation (GFC) - relies on infrared absorbency properties of CO at 4.7, High accuracy, greater sensitivity, more complex equipment, stationary measurement
- Nondispersive Infrared (NDIR) - CO has a characteristic spectrum that allows it to be measured with reference to IR energy absorbed. Sensitive to drift, allows continuous datalogging, requires warm-up time, operable by non-technical personnel
OSHA PEL=50 ppm TWA
NIOSH REL=35 ppm TWA; 200 ppm ceiling
NIOSH IDLH=1,200 ppm
ACGIH TLV=25 ppm TWA
EPA NAAQS (Primary Standard) for outside air=9 ppm (TWA 8 hrs), =35 ppm (TWA 1 hr). This was established to protect public health (susceptible populations)
Applicable IH Standards
DFG MAK (Germany) TWA = 30 ppm PEAK = 60 ppm (30 min)
Japan (JSOH) TWA = 50 ppm
HSE OES (United Kingdom) TWA = 50 ppm STEL = 300 ppm
Reference: “TLVs and Other Occupational Exposure Values”
Still More TLV’s (International Flavor)
NRC (1987) EEGLs: 10 min = 1,500 ppm 30 min = 800 ppm 60 min = 400 ppm 24 hrs = 50 ppm
NRC = National Research Council
EEGL is Emergency Exposure Guidance Levels
Canadian IAQ Residential Exposure Guidelines: <11 ppm for 8 hrs, <25 ppm for 1hr (ASTER)
WHO Concentration of Concern is >30 ppm
My project was a simulation of lawn care worker.
8 hour work day (~ 6 hrs of mowing)
work equipment varied
some CO exposure expected
Mowed two properties.
One property was approximately 1 acre and was mowed with push mower
2nd property was about 2.5 acres and was mowed by riding mower
CO Study, Occupation: Lawn Care Worker
Specific Job Duties of Worker During Study Period
- To operate gasoline powered mowers to mow two properties
- Edging not included
- To obtain gas for mower if empty
Question: Will CO Exposure exceed any standards or guidelines during a simulated average 8-hour work shift for an Lawn Care Worker?
There seems to be few published reports on this type of a study. Some reports focus on small gasoline engines used inside buildings where the CO is easily concentrated.
Subject of Study:
Equipment in Use
- Push mower
- riding lawn tractor
- automobile (to move between sites)
IH Equipment Used for Hazard Assessment
- Metrosonics PIM 1100 Industrial Hygiene Personal Monitor - Courtesy of Metrosonics, Inc.CO Electrochemical Oxidation Sensorwith a Heat Stress Monitor (core temperature and heart beats per minute)with Noise monitor (slow, A-weight)
- Minimum 0 ppm
- Average 5 ppm
- Maximum 150 ppm
- 15 min STEL 13 ppm
- TWA 5 ppm
Comparison to Exposure Guidelines and Standards
- The OSHA PEL TWA was not exceeded.
- The NIOSH REL TWA was not exceeded.
- The NIOSH Ceiling was not exceeded.
- The ACGIH TLV was not exceeded.
- None of the other suggested guidelines were exceeded.
The momentary CO level measured during the start-up of the riding mower was elevated, however the duration of the exposure was short.
Graph of Data (available as handout)
Breaks and Lunch are distinct on data graph
Comments on Data
Possible CO Hazard Control Measures (if needed)
- Eliminate - ex. Substitute gas mower with electric or manual mower.
- Control Source - ex. Adjust equipment to control emissions (catalytic converters) or improve efficiency of combustion process
- Apply appropriate ventilation or exhaust mechanism (only inside enclosures), ensure proper operation of exhausts
More CO Hazard Control Measures
- Provide appropriate personal protective equipment (PPE) to workers, when sources can not be controlled or eliminated and levels are suspected as hazardous. SCBA (NIOSH specified) is often specified. Definitely applies to fire/rescue personnel.
Carbon Monoxide exposure is a serious health and safety hazard.
CO is especially a hazard in enclosed spaces
CO did not seem to be a serious hazard during normal mowing operations.
If CO levels were high and exceeded applicable TLVs, Control measures could be effectively instituted.
Summary of Key Points
Conclusion: No CO Standards or Guidelines Exceeded
- If this simulation was representative of a normal workday of a lawn care worker, then it appears that CO does not pose a serious threat to normal healthy adults.
- It is conceivable that that these low level exposures may cause measurable effects in susceptible individuals. More data is needed.
Injuries (overturned tractors, cuts, eye injuries, thrown debris)
UV radiation exposure
exposure to bioaerosols (mold spores, pollen) - a problem for asthmatics and allergy sufferers
Note: Other Potential Hazards Associated w/ Featured Occupation
Note: CO can be a Hazard in Nonoccupational Settings
- Nursing Homes
- Thanks goes to:
- Jennifer, Ed Williams and Mary Gestaldi for use of their property (land and work equipment)
- James Slattery from Metrosonics, Inc. for use of IH equipment