Letters of Interpretation

OSHA requirements are set by statute, standards, and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. Each letter constitutes OSHA's interpretation of the requirements discussed.

Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information.

These letters of interpretation and the standards they address may not apply to OSHA State Plans. State Plans are required to have standards and enforcement programs that are at least as effective as OSHA's and may have different or additional requirements. Please see OSHA-approved State Plans for more information.

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Date Title Standard Number
The intervals between physical examinations for employees performing interior structural firefighting. 1910.134, 1910.156
Use of non-approved respirators and improper use of approved respirators 1910.134(d)(1)(ii)
Ventilation for an anhydrous ammonia refrigeration system. 1910.134, 1910.307(b), 1910.1000, 1910.1200
Respirator rules as applied to open hatch gauging of sour crude oil storage tanks. 1910.134
NIOSH eliminates maximum use concentrations (MUC) labeling requirement for Chemical Cartridges. 1910.134(d)(1)(ii)
Respirators required during initial hazardous waste site entry 1910.120(c)(4)(ii), 1910.120(g), 1910.134
Use of Air-Purifying Respirators In Dangerous Concentrations of Gases Or Vapors 1910.134, 1910.134(c), 1910.134(d), 1910.134(g), 1910.134(h), 1910.134(k)
Sampling Procedures for Employees Using Air-Supplied Respirators 1910.134
Respiratory protection requirements for sour crude oil tank operations. 1910.134
Respiratory Protection for Mercury and Chlorine 1910.134
Respiratory protection compliance responsibility for contract workers and visitors. 1910.134
Use of eyeglass inserts or spectacle kits inside respirator full facepieces. 1910.134
Acceptance of closed-circuit self-contained breathing apparatus for firefighting. 1910.134
Protection provided by powered air-purifying respirators. 1910.134(g)(1)(i), 1910.134(g)(1)(ii), 1910.134(g)(1)(iii)
Hair where the mask edges meet the skin is not permitted for wearers of 30 minute positive pressure SCBA respirators. 1910.134(g)(1)(i), 1910.134(g)(1)(ii), 1910.134(g)(1)(iii)
Couplings used in supplied air respirator systems. 1910.134(i)(8)
The M-17 gas mask may not be used by workers other than enlisted military personnel. 1910.134
Alarm requirements for breathing air compressors;Respirators for paint materials containing TDI or MDI;Full facepiece respirators are required when eye irritation is experienced. 1910.134(i), 1910.134(d)
Standard for exposure to tetrahydrofuran; Respirators may be worn only if engineering and administrative controls are not feasible. 1910.1000, 1910.134
Facial hair in the face sealing area is unacceptable. 1910.134(g)(1)(i), 1910.134(g)(1)(ii), 1910.134(g)(1)(iii)