Skip Navigation
Safety guides and audits to make your job as a safety professional easier

Controlling Confined Space Hazards


Once hazards are identified, it is critical to institute appropriate control measures to eliminate or, if not possible, reduce and control confined space hazards. This module discusses the "Hierarchy of Controls" strategies to control confined space hazards. The moment of entry is critical in confined or enclosed space operations. Injuries from fires, explosions, falls, and unsafe atmospheres may be avoided with careful preparation and adequate testing. Remember, acceptable entry conditions must be attained before entry and those safe conditions must be maintained throughout the duration of an entry. This module also explains some of the procedures and precautions that should be in place to safeguard entrants while they are working in the confined space.

Hazard Elimination and Substitution


The highest priority in controlling hazards in confined spaces should be given to the attempt to totally eliminate the hazard so that entry will be completely safe. That's not possible in many situations, but the attempt should still be considered. For instance, if there is a hazardous atmosphere in the confined space, forced-air ventilation of the space might be the answer to completely eliminate the hazard.


If elimination is not possible, it may be acceptable to replace toxic substances with less toxic or non-toxic substances to that hazardous atmospheres are not created. One primary control measure effective in preventing toxic hazardous atmospheres from developing in the first place is the use of less toxic products that vaporize less readily. Keep less of the product at the site and keep containers closed inside the confined space at all times.

1. Which of the following should be considered the top priority in the Hierarchy of Control strategies?

a. Elimination
b. Substitution
c. Engineering controls
d. Administrative controls

Next Section

Confined Space Hazards by Ally Safety

Confined Space Engineering Controls

Engineering controls may be employed to control hazards through design or redesign a confined space so that hazardous atmospheres and substances do not develop in the workspace. Examples of engineering controls include:

  • installing automatic ventilation systems;
  • redesigning the entrance so that unlimited access is possible; and
  • redesigning an old confined space with a safer configuration.

Confined Space Administrative Controls

Administrative controls attempt to mitigate or eliminate exposure to hazards through changes in policies and procedures, and work practices such as:

  • rotating workers;
  • safe entry procedures; and
  • good housekeeping practices.

Confined spaces should be cleaned/decontaminated of hazardous materials to the extent feasible before entry. Cleaning/decontamination should be the preferred method of reducing exposure to hazardous materials. PPE should be worn by confined space entrants to provide appropriate protection against the hazards which may be present.

Personal Protective Equipment (PPE)

If the hazard cannot be eliminated or reduced to a safe level through engineering and/or administrative controls, PPE should be used. A qualified person should determine the types of PPE needed by entrants, including rescue teams.

2. What should be the preferred method of reducing exposure to hazardous materials in a confined space?

a. Designing automatic detectors
b. Cleaning/decontamination
c. Force air ventilation
d. Purging with nitrogen

Next Section

Controlling Toxic Atmospheres

One primary control measure effective in preventing toxic hazardous atmospheres from developing in the first place is the use of less toxic products that vaporize less readily. Keep less of the product at the site and keep containers closed inside the confined space at all times.

Selecting the Right Blower - Air Systems

Ventilating Confined Spaces

Ventilation is one of the most common control methods used in confined spaces to eliminate hazardous atmospheres.

Ventilation helps to:

  • Provide adequate oxygen to the air in the space.
  • Control atmospheric contaminants.
  • Prevent fire and explosion hazards.
  • Control heat and humidity.

When ventilation is used to remove atmospheric contaminants from the confined space, the space should be ventilated until the atmosphere is within the acceptable ranges. Ventilation should be maintained during the occupancy if there is a potential for the atmospheric conditions to move out of the acceptable range.

Once it has been determined that the confined space contains a harmful atmosphere, the next step is to clear it. Ventilation blows out oxygen-deficient or contaminated atmospheres and replaces harmful vapors with clean, fresh air. Make sure to ventilate the space thoroughly so that there are no contaminated pockets left, and then test the atmosphere again.

For permit spaces that are deep or have areas leading away from the entry point, the atmosphere may be layered or may be different in remote areas. For these spaces, testing must be done in the area surrounding the worker, which is considered four (4) feet in the direction of travel and to each side. If a sample probe is used to do the testing, then the worker must move slowly enough so that testing is completed, keeping the equipment "response time" in mind, before he/she moves into the new area.

Welding, cutting, burning, and continuous brazing generate hazardous fumes and dusts that can be more effectively removed by local exhaust ventilation systems at or near the point of generation.

When ventilation is not possible or feasible, alternate protective measures or methods to remove air contaminants and protect occupants should be determined by the qualified person prior to authorizing entry.

Continuous Forced Air Conditions

Conditions regarding continuous forced air ventilation should be used as follows:

  • Employees should not enter the space until the forced air ventilation has eliminated any hazardous atmosphere,
  • Forced air ventilation should be so directed as to ventilate the immediate areas where an employee is or will be present within the space,
  • Continuous ventilation is maintained until all employees have left the space, and
  • Air supply for forced air ventilation should be from a clean source.

3. When testing for hazardous atmospheres in a confined space, the area surrounding the worker is considered _____.

a. a 5-foot "bubble" around, above, and below the worker
b. no more than 6 feet in front of the worker
c. 4 feet in the direction of travel and to each side
d. to be within arms-length in each direction

Next Section

Continue ventilation and frequent atmospheric testing for the entire duration of entry.

Proper Ventilation Considerations

Initially determine:

  • Number and size of openings.
  • Volume and configuration of the space to be entered.
  • Capacity and positioning of the ventilation equipment to be used.
  • Existing and potential atmospheric hazards.

After beginning ventilation:

  • Routinely test the confined space until levels stabilize at acceptable entry conditions.

Once entry and work start:

  • Continue ventilation and frequent atmospheric testing for the entire duration of entry.
  • Consider atmospheric hazards created by work in the space.

4. When is ventilation required for work in a confined space?

a. For the entire duration of the entry
b. Until testing determines a safe atmosphere
c. Every 30 minutes while work is conducted
d. When testing detects a change in conditions

Next Section

Respiratory Protection

Respirator used during rescue training - USAF

Respirators protect workers against insufficient oxygen environments (less than 19.5%), harmful dusts, fogs, smokes, mists, gases, vapors, and sprays. These hazards may cause cancer, lung impairment, diseases, or death.

Respirators protect the user in two basic ways.

  • The first is by the removal of contaminants from the air. Respirators of this type include particulate respirators, which filter out airborne particles, and air-purifying respirators with cartridges/canisters which filter out chemicals and gases.
  • Other respirators protect by supplying clean respirable air from another source. Respirators that fall into this category include airline respirators, which use compressed air from a remote source, and self-contained breathing apparatus (SCBA), which include their own air supply.
Respirators in the Workplace - OSHA

Respiratory protection is needed in confined spaces whenever:

  • An emergency exists and entry cannot be delayed. Assume that an IDLH atmosphere exists.
  • There is an inert atmosphere or testing shows that an IDLH exists and additional ventilation cannot reduce concentrations to safe levels.
  • Current testing indicates atmosphere to be safe, but unsafe conditions could reasonably be expected to develop at any time.

5. Respiratory protection in a confined space would NOT be necessary when _____.

a. an IDLH condition is assumed to exist
b. inert gases could rise to unacceptable levels
c. an unsafe condition is possible
d. oxygen levels are at or above 19.5%

Next Section

Confined Space Inspections

Inspecting your confined space entry program, procedures, and practices is very important.

Inspecting your confined space entry program, procedures, and practices is an important part of the safety management system evaluation. Use a checklist like this to help identify strengths and weaknesses in the program.

Sample Confined Space Inspection Checklist

  1. _____ Are confined spaces thoroughly emptied of any corrosive or hazardous substances, such as acids or caustics, before entry?
  2. _____ Are all lines to a confined space, containing inert, toxic, flammable, or corrosive materials valved off and blanked or disconnected and separated before entry?
  3. _____ Are all impellers, agitators, or other moving parts and equipment inside confined spaces locked-out if they present a hazard?
  4. _____ Is either natural or mechanical ventilation provided prior to confined space entry?
  5. _____ Are appropriate atmospheric tests performed to check for oxygen deficiency, toxic substances and explosive concentrations in the confined space before entry?
  6. _____ Is adequate illumination provided for the work to be performed in the confined space?
  7. _____ Is the atmosphere inside the confined space frequently tested or continuously monitored during conduct of work?
  8. _____ Is there an assigned safety standby employee outside of the confined space when required, whose sole responsibility is to watch the work in progress, sound an alarm if necessary, and render assistance?
  9. _____ Is the standby employee appropriately trained and equipped to handle an emergency?
  10. _____ Is the standby employee or other employees prohibited from entering the confined space without lifelines and respiratory equipment if there is any question as to the cause of an emergency?
  11. _____ Is approved respiratory equipment required if the atmosphere inside the confined space cannot be made acceptable?
  12. _____ Is all portable electrical equipment used inside confined spaces either grounded and insulated, or equipped with ground fault protection?
  13. _____ Before gas welding or burning is started in a confined space, are hoses checked for leaks?
  14. _____ Are compressed gas bottles forbidden inside of the confined space?
  15. _____ Is the confined area tested for a flammable/explosive atmosphere prior to using electrical equipment/lights within the confined space?
  16. _____ If the confined space may contain a potentially flammable/explosive atmosphere, are only intrinsically safe equipment and lights used within the confined space?
  17. _____ If employees will be using oxygen-consuming equipment-such as salamanders, torches, and furnaces, in a confined space, is sufficient air provided to assure combustion without reducing the oxygen concentration of the atmosphere below 19.5 percent by volume?
  18. _____ Whenever combustion-type equipment is used in a confined space, are provisions made to ensure the exhaust gases are vented outside of the enclosure?
  19. _____ Is each confined space checked for decaying vegetation or animal matter which may produce methane?
  20. _____ Is the confined space checked for possible industrial waste which could contain toxic properties?
  21. _____ If the confined space is below the ground and near areas where motor vehicles will be operating, is it possible for vehicle exhaust or carbon monoxide to enter the space?

6. What is a common tool to discover actual confined space conditions and program strengths and weaknesses?

a. A brainstorming session
b. A checklist
c. A statistical analysis
d. A safety committee discussion

Check your Work

Read the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.


Dangers of Confined Spaces

Next Module

OSHAcademy Ultimate Guide Banner Ad