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Confined Spaces – Part 1. An Overview of the WISHA Confined Spaces Standard. Purpose of This Module.

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Confined Spaces – Part 1

An Overview of the

WISHA Confined Spaces Standard

purpose of this module
Purpose of This Module

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.

confined spaces overview
Confined Spaces Overview

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.

identifying the space
Identifying the space

What is a confined space?

A confined space is an enclosed space that:

  • is large enough to get whole body inside,

is not designed for human occupation,

has limited or restricted entrance or exit.

It must have all three characteristics to be a confined space.

identifying confined spaces
Identifying Confined Spaces

Examples of confined spaces

Manholes & Sewers



Grain storage bins

Other examples include vaults, pipelines, tank cars, and ship holds

hazards of confined spaces
Hazards of Confined Spaces

Basic Principles

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.

hazards of confined spaces1
Hazards of Confined Spaces

What are the main hazards of confined spaces?

  • Hazardous atmospheres
  • Engulfing materials
  • Entrapment
  • Moving parts
  • Electricity
hazard of confined spaces
Hazard of Confined Spaces

When is a confined space so dangerous a written entry permit system is required?

  • When there is an actual or potential “hazardous atmosphere” or
  • when the space contains loose material that can engulf a person, or
  • when the space is configured in a way that can trap a person, or
  • when there is any other recognized serious safety and health hazard.
hazard identification
Hazard Identification

A “hazardous atmosphere” in a confined space has one or more of the following:

Flammable gas, mist or vapor

Flammable dusts

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.

hazard identification1
Hazard Identification

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”

hazard identification2
Hazard Identification

Example of flammable gas levels - Methane





Too Rich

Too Lean










An open flame or a spark will cause an explosion when methane amount is between 5.3% and 15%, the upper flammable limit (UFL).

hazard identification3
Hazard Identification

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 content

Oxygen deficiency exists

hazard identification4
Hazard Identification

Effects of Oxygen Deficiency

% OxygenSymptoms

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.

hazard identification5
Hazard Identification

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

hazard identification6
Hazard Identification

Hazardous Atmospheres – Toxic Chemicals

  • At very high levels, most chemicals in the air can be immediately life-threatening or cause permanent bodily harm.
  • At lower levels, chemicals in the air can still cause harm.


  • Most chemicals have “permissible exposure limits” (PELs) which will cause harm if exceeded.
  • Even non-toxic or low-toxic chemicals can replace oxygen if levels are high enough.
hazard identification7
Hazard Identification

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.

hazard identification8
Hazard Identification

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

Coughing,red eyes

Unconscious in 30 min.

Instant collapse

hazard identification9
Hazard Identification

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

hazard identification10
Hazard Identification

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.

hazard identification11
Hazard Identification

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

hazard identification12
Hazard Identification

Other Recognized Hazards

Electrical lines, steam lines or hydraulic lines

Mechanical hazards (moving parts)

Hazards caused by the work

(welding, painting etc.)

controlling the space
Controlling the Space

The hazards of a confined space can be be controlled in the following ways:

  • Prevent employee entry.
  • Remove or reduce hazards in the space first, before a person enters.
  • If hazard cannot be controlled, you must use a written permit system to enter safely.

See Part 2 for more information on a written permit system.

controlling the space1
Controlling the Space

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.

hazard control
Hazard Control

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.

hazard control1
Hazard Control

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.

hazard elimination
Hazard Elimination

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 can t be eliminated
If Hazards Can’t Be Eliminated

If hazards cannot be completely eliminated, there are only two options:

a complete written permit system, or

“alternate procedures.”

Both require training of employees.

See Part 2 for more information on entry procedures.

additional information
Additional Information

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:

confined space quiz
Confined Space Quiz

Question 1

Which of following are considered confined spaces?

  • A sewer manhole
  • A sub-basement vault with only one door
  • A 20 foot deep ditch
  • A 30-gallon drum
confined spaces quiz
Confined Spaces Quiz

Question 2

When can a hazardous atmospheres be fatal?

  • When there is not enough air
  • When there is 2% methane
  • When there is 10% oxygen
  • When there is no ventilation
confined spaces quiz1
Confined Spaces Quiz

Question 3

Which of the following is not a good way to control hazardous atmospheres?

  • Ventilate for two hours before entering
  • Drain or pump out liquid contents
  • Air test and ventilate continuously
  • Remove any sludge from outside the space