Know Your Permit Space Air Monitoring Requirements

Atmospheres in permit-required confined spaces can be very unpredictable. That’s why OSHA has specific requirements to test the air and protect workers who enter permit spaces. In fact, inhaling hazardous substances in confined spaces led to 126 worker deaths between 2011 and 2018. The most common types of inhaled gases were:

  • Hydrogen sulfide,
  • Carbon monoxide,
  • Methane,
  • Sewer gas, and
  • Solvents and degreasers.

In addition to these inhalation deaths, there were 39 cases of depletion of oxygen and 21 cases of drowning. These fatalities occurred in:

  • Oil storage tank interiors;
  • Underground caves, mines and tunnels;
  • Sewers, manholes and storm drains;
  • Confined spaces on vehicles;
  • Tanker truck interiors; and
  • Manure pits.

Air monitoring of permit-required confined spaces must be done before entry is authorized and as necessary to determine if acceptable entry conditions are being maintained during entry operations. (MR.Zanis –

What is a Hazardous Atmosphere?

OSHA defines a hazardous atmosphere in 1910.146 as one that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue (escape unaided from a permit space), injury or acute illness from one or more of the following causes:

  • Flammable gas, vapor or mist in excess of 10% of its lower flammable limit (LFL);
  • Airborne combustible dust at a concentration that meets or exceeds its LFL;
  • Note: This concentration may be approximated as a condition in which the dust obscures vision at a distance of 5ft (1.52m) or less.
  • Atmospheric oxygen concentration below 19.5% or above 23.5%;
  • Atmospheric concentration of any substance for which a dose or a permissible exposure limit (PEL) is published in 1910 Subpart G, Occupational Health and Environmental Control, or in Subpart Z, Toxic and Hazardous Substances, and which could result in employee exposure in excess of its dose or PEL;
  • Any other atmospheric condition that is immediately dangerous to life or health.

For air contaminants for which OSHA has not determined a dose or PEL, other sources of information, such as Safety Data Sheets (SDSs) that comply with the Hazard Communication Standard at 1910.1200, published information and internal documents can provide guidance in establishing acceptable atmospheric conditions.

OSHA has specific requirements to test the air and protect workers who enter permit spaces. (Tanakorn –

When Must the Air Be Monitored?

Air monitoring must be done before entry is authorized and as necessary to determine if acceptable entry conditions are being maintained during entry operations. If the space is too large to isolate, perform testing to the extent feasible before entry—and continuously where entrants are working.

The atmosphere must be tested using the steps identified on the permit, and the results (the actual test concentrations) must be recorded on the permit near the levels identified for safe entry. OSHA requires you test in this order:

  • Test for oxygen first,
  • Then for combustible gases and vapors, and
  • Then for toxic gases and vapors.

Who Monitors the Air?

The rule states that:

  • The person in charge must know the proper use and calibration of monitoring equipment and supervise its use.
  • Authorized entrants must know how to use the testing and monitoring equipment.
  • Employees entering the space must be allowed to observe the initial monitoring of the space.

Keeping Things Clear

A clear communication system must be established between the authorized entrants and the attendant stationed outside the confined space. This should include a means for the entrants to alert the attendant if they detect any hazardous conditions and in the event of an emergency.

Attendants must:

  • Know the hazards that may be faced during entry, including information on the signs, symptoms and consequences of the exposure;
  • Be aware of possible behavioral effects of hazard exposure in authorized entrants;
  • Continuously maintain an accurate count of authorized entrants in the permit space;
  • Remain outside the permit space during entry operations until relieved by another attendant;
  • Communicate with authorized entrants as necessary to monitor entrant status and to alert entrants of the need to evacuate the space;
  • Perform non-entry rescues as specified by the employer’s rescue procedure; and
  • Perform no duties that might interfere with the attendant’s primary duty to monitor and protect authorized entrants.

What’s Required for Employee Training?

Employers must provide the training specified in 1910.146(g). This requires employees to be trained so they have the understanding, knowledge and skills necessary for the safe performance of the duties assigned to them. Retraining is needed when there are new or revised procedures. Finally, employers must certify that training has taken place and that the certification is available for inspection by employees and their authorized representatives.

Key to Remember: Atmospheric testing is required to evaluate the air in the permit-required confined space; verify that conditions for entry are acceptable; and ensure conditions remain acceptable during entry operations.

About the Author:

Rachel Krubsack is an Editor on the Environmental, Health, and Safety (EHS) team at J. J. Keller & Associates, Inc. Rachel edits two manuals–OSHA Rules for General Industry and Hazard Communication Compliance. She also contributes content to Safety Management Suite and Compliance Network and various trade publications. Her topics of expertise include hazard communication, hearing conservation and OSHA general industry training requirements. In 2023, she completed OSHA 30 training for general industry. Rachel has a BA in English from Loras College in Dubuque, Iowa, and a master’s degree in library and information science from the University of Wisconsin Milwaukee.

Share on Socials!

Related Articles

Related Articles

Listen Up! From the NHCA Experts…

Safe-in-Sound Award: Real-World Successes in Hearing Loss Prevention By: Thais C. Morata, NIOSH Senior Research Audiologist and NHCA Expert Figure 1: Team that conducted a site ...
Read More

Apache Helicopter Wins Safe-in-Sound Award

Mesa site employees testing an original prototype of the hush kit (Photo courtesy NIOSH) The National Institute for Occupational Safety and Health (NIOSH), in partnership with ...
Read More

Five Things to Know for an Effective Written Respiratory Program

Robin Regan, Contributor Protection against respiratory hazards is more than a nuisance—exposure to dust, gases and vapors can lead to serious, life-threatening diseases. (photo courtesy Honeywell ...
Read More

Follow IHW!


Sign up to receive our industry publications for FREE!

Industrial Hygiene

Construction Safety