Confined Spaces – Part 1. An Overview of the WISHA Confined Spaces Standard. Purpose of This Module.
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An Overview of the
WISHA Confined Spaces Standard
This two-part module provides basic information for employers about the hazards of confined spaces, how to control these hazards and what WISHA requirements apply when employees enter confined spaces.
Some employers may elect to contract out confined space work. In those cases, employers are obligated to fully inform contractors of the confined space hazards at their facilities.
This overview does not replace the confined spaces standard. For the complete WISHA confined space rule requirements, see Confined Spaces Chapter 296-62 Part M.
Part 1 of this overview will cover the following:
How to identify a confined space,
Confined space hazards,
How to control or eliminate the hazards.
What is a confined space?
A confined space is an enclosed space that:
is not designed for human occupation,
has limited or restricted entrance or exit.
It must have all three characteristics to be a confined space.
Examples of confined spaces
Manholes & Sewers
Grain storage bins
Other examples include vaults, pipelines, tank cars, and ship holds
Confined spaces can be deadly.
Some confined spaces are more hazardous than others.
Confined space conditions can change rapidly from no hazards to life-threatening hazards.
Some confined spaces are so hazardous, a written permit system is required for entry.
The hazards of confined spaces can often be controlled or eliminated before entering.
For a description of an actual confined space fatality,click here.
What are the main hazards of confined spaces?
When is a confined space so dangerous a written entry permit system is required?
A “hazardous atmosphere” in a confined space has one or more of the following:
Flammable gas, mist or vapor
Oxygen content below 19.5% or above 23.5%
Air contaminant concentrations that would cause death, incapacitation, or permanent health problems
You must do air monitoring to determine if a hazardous atmosphere exists.
Hazardous Atmospheres – Flammable Gases,
Vapors and Dusts
Flammable gases, vapors or dusts will ignite from a spark or flame if above a level in the air called the “lower flammable limit” (LFL).
Gas or vapor levels higher than 10% of the LFL are considered hazardous and the confined space cannot be entered until levels are reduced.
Amounts above 10% of the LFL are usually toxic as well.
LFL is sometimes called “LEL” – “lower explosive limit”
Example of flammable gas levels - Methane
An open flame or a spark will cause an explosion when methane amount is between 5.3% and 15%, the upper flammable limit (UFL).
Hazardous Atmospheres – Oxygen Deficiency
A reduction in oxygen is caused by tank rusting, microbe activity, or replacement by another gas.
Lack of oxygen can cause a person to immediately collapse and die.
Normal air contains 21% oxygen. A space with oxygen content below 19.5 % is considered “oxygen deficient”.
Oxygen deficiency exists
Effects of Oxygen Deficiency
19.5% - 16% Fatigue, mild impaired coordination
16% - 12% Increased breathing rate and pulse; impaired coordination, perception or judgment
12% - 10% Further increased breathing rate, blue lips, mental confusion
10% - 8% Fainting, nausea, vomiting, mental confusion within few minutes
8% - 6% Collapse, death within 8 minutes
6% - 0% Coma within 40 seconds, death
Using an “inerting gas” like nitrogen, to counteract flammable vapors will result in an oxygen deficiency.
A word about oxygen-enriched atmospheres
A confined space with oxygen amount above 23.5% is considered “oxygen-enriched”.
The source of extra oxygen is typically from leaking oxygen cylinders used for oxy-acetylene torches.
Oxygen above 23.5% is a fire or explosion hazard.
Green tanks contain oxygen
Hazardous Atmospheres – Toxic Chemicals
Hazardous Atmosphere – Toxic Chemicals
The most common toxic chemicals in confined spaces fatalities are hydrogen sulfide and carbon monoxide.
Other toxic chemicals can include welding fumes, vapors from liquid residues in storage tanks, or chemical products used in the confined space.
Chemicals can quickly reach toxic levels in the air of a confined space, especially gases, solvent vapors or sprayed products.
Hazardous Atmospheres–Hydrogen Sulfide (H2S)
Hydrogen sulfide gas is commonly found in sewers.
It can be instantly fatal at higher levels in a confined space.
Disturbing sewage sludge can release more hydrogen sulfide gas.
H2S in ppm
Smell strong odor
Loss of smell
Death in minutes
Unconscious in 30 min.
Hazardous Atmospheres – Carbon Monoxide (CO)
Carbon monoxide comes from operating internal combustion engines in or near confined space.
Propane-powered engines also emit carbon monoxide.
Fatal levels of CO are quickly reached in confined spaces.
Propane-powered manlift in a large tank
The PEL for CO is 35 ppm. To see the effects of CO, click here
What are the Hazards of Engulfing Material?
Engulfing materials include liquids or loose solids such as grain, sand or other granular material.
People cannot escape when caught in moving loose solids and usually suffocate.
Workers often get engulfed when in-feed or out-feed lines are inadvertently opened or activated.
What is Entrapment?
The space is configured in a way that can trap a worker, for example, sides sloping towards the center
Gravel hopper with sloping internal sides
Other Recognized Hazards
Electrical lines, steam lines or hydraulic lines
Mechanical hazards (moving parts)
Hazards caused by the work
(welding, painting etc.)
The hazards of a confined space can be be controlled in the following ways:
See Part 2 for more information on a written permit system.
Warning employees and controlling access
Post warning signs at the entrance of confined spaces.
Limit employee access to confined spaces by using entry barriers or locks.
Make sure that unauthorized workers do not enter the confined space.
How To Control Hazardous Atmospheres
Drain or pump out liquid contents, if any.
Blank off all in-feeding lines.
Air test and ventilate.
Continue ventilating constantly.
If possible, remove any sludge from outside the confined space.
Exit space if conditions deteriorate.
Hazardous Atmospheres Dangers
It is difficult to eliminate hazardous atmospheres in most sewers lines.
Tank sludge or sewer sludge can release toxic gases during cleanup.
Toxic or flammable gases can exist in pockets or layers.
How To Eliminate Physical Hazards
Lock-out moving parts
Blank or block steam pipes and product in-feeding pipes.
De-energize electrical parts or wiring
If hazards cannot be completely eliminated, there are only two options:
a complete written permit system, or
Both require training of employees.
See Part 2 for more information on entry procedures.
More information is available on WISHA webpage
This presentation is just an overview and does not cover all requirements.
For more information on how to put together a confined space program for your workplace, go to:
For additional assistance, you can call one of our consultants. Click below for local L & I office locations:
Which of following are considered confined spaces?
When can a hazardous atmospheres be fatal?
Which of the following is not a good way to control hazardous atmospheres?