Hazardous atmospheres procedures

This section does not apply when one or more specific sections cover the situation. Employers should use the provisions in 1917.22 Hazardous cargo, 1917.24 Carbon monoxide, 1917.25 Fumigants, pesticides, insecticides and hazardous preservatives, 1917.73 Terminal facilities handling menhaden and similar species of fish, 1917.152 Welding, cutting, and heating (hot work), or 1917.153 Spray painting when those topics apply, as explained in 1917.23(a).

A designated and appropriately equipped person must test the atmosphere before employees enter any room, building, vehicle, railcar, or other space that contains or has contained a hazardous atmosphere. See 1917.23(b)(1).

Employers must retain the results of any tests required by this section for at least 30 days. The record should include test results that demonstrate whether a hazardous atmosphere existed and the date and location of the testing, as required by 1917.23(b)(2).

A designated person must perform tests when mechanical ventilation is used to ensure the atmosphere remains safe and not hazardous. This continuous or periodic testing verifies the ventilation controls are effective, as required in 1917.23(c).

Only designated persons may enter hazardous atmospheres, and those persons must be protected by respiratory and emergency protective equipment meeting the requirements of subpart E of part 1917. See 1917.23(d) and 1917.23(d)(1).

Persons entering a hazardous atmosphere must be instructed in the nature of the hazard, precautions to take, and how to use protective and emergency equipment, and a similarly equipped and instructed standby observer must continuously monitor employees inside the space. See 1917.23(d)(2).

Employees may not enter atmospheres identified as flammable or oxygen deficient (less than 19.5% oxygen) except for emergency or rescue operations; in those emergency cases, entrants must be trained in the hazards and must use self-contained breathing apparatus. See 1917.23(d)(3). For clarification about how OSHA regards oxygen-deficient atmospheres and respirator use, consult OSHA’s interpretation on Oxygen-deficient atmospheres in HVAC, which references the respiratory protection requirement for atmospheres below 19.5% oxygen.

Employers must post appropriate warning signs or use equivalent means at all means of access to spaces identified with hazardous, flammable, or oxygen-deficient atmospheres to prevent inadvertent employee entry. See 1917.23(d)(4).

Designated employees must clean up asbestos cargo spills and must be protected from asbestos hazards as required by 1910.1001, per 1917.23(e). Employers should also review OSHA's Asbestos remediation protocols letter of interpretation, which explains when remediation activities may fall under the construction asbestos standard (29 CFR 1926.1101) rather than the general industry standard.

An "appropriately equipped" designated tester must have instruments and personal protective equipment capable of detecting the relevant hazardous conditions (for example, oxygen level, flammability/LEL, and known toxic contaminants) so they can determine whether the atmosphere is hazardous before entry, as required by 1917.23(b)(1).

Atmosphere tests must be made by a designated person while mechanical ventilation is used to ensure the atmosphere remains non-hazardous; the frequency should be sufficient to confirm ventilation effectiveness and worker safety as described in 1917.23(c).

A standby observer must be similarly equipped and instructed and must continuously monitor the activity of employees within the space, prepared to initiate emergency procedures if needed, per 1917.23(d)(2).

Personnel required to enter flammable or oxygen-deficient atmospheres in emergencies must be instructed in the dangers and trained in the use of self-contained breathing apparatus, which must be utilized for those entries, as provided in 1917.23(d)(3). For additional guidance on oxygen-deficient atmospheres and respirator requirements, see OSHA’s Oxygen-deficient atmospheres in HVAC interpretation.

Yes. Records of test results should identify when and where testing occurred so they meaningfully document whether a hazardous atmosphere existed; these records must be kept for at least 30 days under 1917.23(b)(2).

If carbon monoxide hazards apply, the employer must follow 1917.24 Carbon monoxide rather than the general hazardous atmospheres procedures in 1917.23(a).

Employers may use equivalent measures—such as locked gates, barriers, color-coded tags, or written entry permits that restrict access—to prevent inadvertent entry, provided they effectively deny or warn access to spaces identified as hazardous, flammable, or oxygen deficient as required in 1917.23(d)(4).

Yes. Respiratory and emergency protective equipment used for entry must meet the requirements of subpart E of part 1917, so employers must follow those specific respiratory protection and emergency equipment rules in addition to 1917.23(d)(1).

Work to clean up asbestos-containing building materials may fall under OSHA’s construction asbestos standard (29 CFR 1926.1101) rather than the general industry standard [1910.1001] when the activity qualifies as remediation or repair work; OSHA explains this distinction in the Asbestos remediation protocols interpretation and 1917.23(e) requires protection consistent with 1910.1001.