Respiratory protection requirements

Under 1910.134(a)(1) you must try to prevent contamination of the air by using engineering controls first, and use respirators only when those controls are not feasible or while they are being put in place.

• Employers must prioritize measures such as enclosure, local exhaust ventilation, and substitution of less toxic materials before relying on respirators (1910.134(a)(1)).
• If engineering and administrative controls cannot reduce exposures sufficiently, then provide respirators and a written respiratory protection program (1910.134(a)(2)).

Under 1910.134(a)(2) the employer must provide a respirator to each employee whenever respirator use is necessary to protect their health or when the employer requires respirator use.

• The employer must supply respirators that are appropriate and suitable for the intended purpose and must establish and maintain a written respiratory protection program covering each employee required to use a respirator (1910.134(a)(2)).

Under 1910.134(b) an air-purifying respirator cleans the ambient air by passing it through a filter, cartridge, or canister, while an atmosphere-supplying respirator provides breathing air from a source independent of the workplace atmosphere.

• Air-purifying respirator: removes contaminants from the ambient air via filters, cartridges or canisters (1910.134(b)).
• Atmosphere-supplying respirator (SAR or SCBA): supplies breathing air from a separate source and does not rely on ambient air (1910.134(b)).
• Use atmosphere-supplying respirators for IDLH or oxygen-deficient atmospheres where air-purifying devices cannot protect the wearer.

Under 1910.134, an IDLH atmosphere is one that poses an immediate threat to life, would cause irreversible health effects, or would impair escape; OSHA treats oxygen-deficient atmospheres as IDLH.

• The respiratory protection standard defines IDLH as an atmosphere that poses an immediate threat to life or would cause irreversible adverse health effects (see 1910.134).
• OSHA has explained that oxygen-deficient atmospheres must be considered IDLH and that where civilian employees are covered by OSHA standards they are subject to all requirements in [1910.134], including IDLH protections; see OSHA’s interpretation on oxygen-deficient atmospheres in HVAC contexts (Oxygen-deficient atmospheres in HVAC, 7/16/2024).

Under 1910.134(c) the employer must develop and implement a written respiratory protection program with worksite-specific procedures that include all applicable program elements and be run by a suitably trained administrator.

• Required program elements include: respirator selection procedures; medical evaluations; fit testing for tight-fitting respirators; procedures for routine and emergency respirator use; cleaning, maintenance, storage and inspection schedules; supplied-air quality and flow assurances; training on hazards and respirator use; and procedures for evaluating program effectiveness (1910.134(c) and 1910.134(c)(1)).

Under 1910.134(c)(1)(i) you must use procedures that select respirators based on the contaminant, exposure level, assigned protection factor, and the work to be performed.

• Consider contaminant type (particulate, gas/vapor), concentration relative to exposure limits, whether the atmosphere is IDLH or oxygen-deficient, and the required Assigned Protection Factor (APF).
• Use the Maximum Use Concentration (MUC) calculated from the respirator’s APF and the applicable exposure limit when choosing respirators (see definitions for APF and MUC in 1910.134).
• Ensure cartridges/filters are NIOSH-certified for the hazard and that the chosen respirator is practical for the job and fit-tested for each user (1910.134(c)(1)(i)).

Under 1910.134(c)(1)(ii) any employee who is required to use a respirator (other than for voluntary use where the employer follows the voluntary-use provisions) must have a medical evaluation to determine their ability to safely wear the respirator.

• The employer must have the employee evaluated by a physician or other licensed health care professional (PLHCP) in accordance with the standard before fit testing or respirator use (1910.134(c)(1)(ii)).
• Medical evaluations are also required when medical signs/symptoms develop, when workplace conditions change, or when the type of respirator changes.

Under 1910.134(c)(1)(iii) employers must perform fit testing for every employee required to wear a tight-fitting respirator before initial use, whenever a different respirator model/size is used, and at least annually afterward.

• Fit testing must use either a qualitative fit test (QLFT) or quantitative fit test (QNFT) and follow the protocols in the standard (1910.134(c)(1)(iii)).
• Refit employees who have undergone facial changes or weight changes that could affect fit.

Under 1910.134(c)(1)(iv) you must have clear procedures for when and how respirators are used during both normal operations and reasonably foreseeable emergencies.

• Procedures should specify which respirator type is required in each situation, how to don and doff, communication procedures, limits of use, and actions during emergencies including rescue or evacuation (1910.134(c)(1)(iv)).
• For emergency and IDLH conditions, use atmosphere-supplying respirators and ensure workers are trained and medically cleared.

Under 1910.134(c)(1)(v) the employer must establish procedures and schedules for cleaning, disinfecting, storing, inspecting, repairing, and discarding respirators so they remain effective and safe.

• Provide routine cleaning and disinfection, storage in a clean, dry location protected from contamination, regular inspection for damage, and timely repair or replacement of parts (1910.134(c)(1)(v)).
• Document maintenance schedules and ensure users know how to spot problems that require removal from service.

Under 1910.134(c)(1)(vi) the employer must ensure the breathing air supplied to atmosphere-supplying respirators is of adequate quality, quantity, and flow to protect employees.

• The employer must use breathing air sources and compressors that meet the standard’s quality requirements (oil-free, properly filtered, and tested as required), and ensure sufficient flow and pressure for the respirator type in use (1910.134(c)(1)(vi)).
• Establish procedures for monitoring, maintenance, and documentation of breathing-air systems.

Under 1910.134(c)(1)(vii) and (viii) employees must be trained on the respiratory hazards they face and on proper respirator use, including putting on and removing the respirator, limitations, and maintenance.

• Training must cover the nature of the hazards, how the respirator protects them, limitations, instructions for inspecting, donning/doffing, seal checking, cleaning, storage, and maintenance (1910.134(c)(1)(vii) and 1910.134(c)(1)(viii)).
• Retrain when procedures or equipment change, when fit or use problems occur, or when the evaluation shows inadequate knowledge or skill.

Under 1910.134(c)(1)(ix) the employer must regularly evaluate the respiratory protection program’s effectiveness and update it as needed.

• Conduct periodic evaluations—at least annually and whenever workplace conditions, exposures, respirator types, or personnel change—to ensure the program is working and employees are protected (1910.134(c)(1)(ix)).
• Use observations, employee feedback, fit-test results, medical events, and incident reviews to guide program improvements.

Under 1910.134(c)(2) if respirator use is not required, the employer may allow or provide respirators only after determining that such use will not itself create a hazard, and must give voluntary users specific information from appendix D.

• If voluntary use is permitted, the employer must give users the information in Appendix D ("Information for Employees Using Respirators When Not Required Under the Standard") and must ensure the use will not create a hazard (1910.134(c)(2)).
• The employer must also implement the program elements necessary to ensure voluntary users are medically able to use the respirator and that it is cleaned, stored, and maintained safely (1910.134(c)(2)(ii)).

Under 1910.134(c)(2)(ii) the employer must ensure that voluntary respirator users are medically able to use the respirator and that the respirator is cleaned, stored, and maintained so it does not present a health hazard.

• Even for voluntary use, employers must implement the program elements necessary to verify medical ability and proper cleaning/storage/maintenance (1910.134(c)(2)(ii)).
• If the voluntary respirator is a tight-fitting respirator, a medical evaluation is typically required because fit-testing and tight seals may impose physiological stress.

Under 1910.134(b) APF is the level of respiratory protection expected from a respirator when the employer runs an effective program, and MUC is calculated by multiplying the APF by the applicable exposure limit.

• APF (Assigned Protection Factor) is the workplace level of protection a respirator or class of respirators is expected to provide when used properly (1910.134(b)).
• MUC (Maximum Use Concentration) = APF × required OSHA exposure limit (PEL, STEL, or ceiling). When no OSHA limit exists, employers must determine an MUC using relevant information and professional judgment (1910.134).
• Use the MUC to select respirators that provide adequate protection for the measured or estimated exposure.

Under 1910.134(b) an End-of-Service-Life Indicator (ESLI) is a system that warns the respirator user when the sorbent is nearing saturation or is no longer effective.

• ESLIs are intended to alert users that cartridges or canisters are approaching the end of their useful service life so they can be changed before protection is lost (1910.134(b)).
• If an approved ESLI is not available for a particular contaminant, employers must implement a change-out schedule based on objective information (e.g., breakthrough data, manufacturer recommendations, or workplace monitoring).

Under 1910.134 the employer must have the respiratory protection program administered by a suitably trained program administrator.

• The program administrator should be trained and competent to implement the written program, choose respirators, ensure fit testing and medical evaluations, provide training, and evaluate program effectiveness (1910.134(c)).
• OSHA’s Small Entity Compliance Guide provides criteria and a sample program to help identify a qualified administrator.

Under 1910.134(c)(2) the employer must provide voluntary respirator users with the information contained in Appendix D to the standard.

• Appendix D covers risks of improper respirator use, the importance of medical clearance (if applicable), how to inspect, store, and maintain respirators, and limitations of respirators (1910.134(c)(2)).
• Provide the Appendix D information in writing or other effective formats and ensure users understand that voluntary use still requires safe cleaning and storage per 1910.134(c)(2)(ii).

Under 1910.134 and OSHA’s 7/16/2024 interpretation, OSHA standards do not apply to uniquely military personnel and operations, but they do apply to civilian employees working on equipment, systems, or operations that are not uniquely military.

• Executive Order 12196 and OSHA guidance exclude military personnel and uniquely military systems from OSHA coverage, but civilian employees at military facilities performing non-unique work are covered and must follow [1910.134] protections including those for oxygen-deficient atmospheres (Oxygen-deficient atmospheres in HVAC, 7/16/2024 and 1910.134).

Under 1910.134(c)(3), the employer must designate a program administrator who is qualified by appropriate training or experience commensurate with the complexity of the program.

This means you must:

• Name a person to administer or oversee the program.
• Ensure that person's training and/or experience matches how complicated your respirator program is (for example: number of respirator types, IDLH work, fit testing frequency, cartridge change schedules).

Yes — under 1910.134(c)(4) the employer must provide respirators, training, and medical evaluations at no cost to the employee.

Provide these items free of charge whether use is required by the employer or voluntary (unless the voluntary use exception described separately applies).

No — employers are not required to include employees in the written respiratory protection program if their only use of respirators is voluntary filtering facepieces (dust masks).

That exception means you do not have to fit test, medically evaluate, or fully enroll these voluntary users in the written program unless their use is required by the employer or necessary to protect the worker.

Yes — the employer must select a NIOSH-certified respirator and ensure it is used in compliance with its certification under 1910.134(d)(1)(ii).

That means you must choose respirator models listed by NIOSH for the contaminant and ensure they are used under the conditions specified by the manufacturer and NIOSH certification.

The employer must identify and evaluate respiratory hazards, including a reasonable estimate of employee exposures and the contaminant's chemical state and physical form, as required by 1910.134(d)(1)(iii).

Practical steps to meet this requirement:

• Estimate how much of the hazard workers breathe (sampling, task observation, or best available data).
• Identify whether the contaminant is a gas, vapor, aerosol, or particulate and its chemical form.
• Use that information to select the right respirator type (air-purifying vs. atmosphere-supplying) and cartridges/filters.

Employers must provide respirators from a sufficient number of models and sizes so that the respirator is acceptable to, and correctly fits, the user as required by 1910.134(d)(1)(iv).

In practice:

• Keep multiple sizes (and different models if necessary) so each worker can pass a fit test and wear the respirator comfortably.
• If workers cannot be fitted with available models, obtain other models/sizes until they can be fitted properly.

For IDLH atmospheres, employers must provide either a full facepiece pressure-demand SCBA with a minimum 30-minute service life or a combination full facepiece pressure-demand supplied-air respirator (SAR) with an auxiliary self-contained air supply, per 1910.134(d)(2)(i)(A)–(B).

Additionally:

• Respirators provided only for escape from IDLH atmospheres must be NIOSH-certified for escape from that atmosphere (1910.134(d)(2)(ii)).
• All oxygen-deficient atmospheres must be considered IDLH (1910.134(d)(2)(iii)).

Employers must use the Assigned Protection Factors in Table 1 to select a respirator that meets or exceeds the required level of protection, as described in 1910.134(d)(3)(i)(A).

Practical points:

• Determine the concentration that workers face and the protection required.
• Choose a respirator with an APF equal to or greater than the ratio needed to reduce workplace exposure to an acceptable level.
• When using combination modes (e.g., airline with filter), ensure the APF you rely on matches the respirator’s actual mode of operation.

The employer must select a respirator that keeps the employee's exposure, measured outside the respirator, at or below the Maximum Use Concentration (MUC), as required by 1910.134(d)(3)(i)(B)(1).

Important limits:

• MUC must not be used for IDLH conditions — in IDLH situations employers must use the respirators listed in 1910.134(d)(2) (1910.134(d)(3)(i)(B)(2)).
• If the MUC calculation exceeds the IDLH level or exceeds cartridge/canister performance limits, the employer must limit the MUC to that lower value (1910.134(d)(3)(i)(B)(3)).

An APR may be used for gases and vapors only if it is equipped with a NIOSH-certified End-of-Service-Life Indicator (ESLI) for the contaminant, or if there is no appropriate ESLI the employer implements a cartridge/canister change schedule based on objective data to ensure replacement before service life ends, per 1910.134(d)(3)(iii)(B)(1)–(2).

Practical steps:

• Use cartridges/canisters with an ESLI when one exists for the contaminant and work conditions.
• If no ESLI exists, document and follow a data-driven change schedule (e.g., exposure monitoring, breakthrough data, manufacturer guidance) and describe the basis in your written program (1910.134(d)(3)(iv)).

Employers must provide either an atmosphere-supplying respirator or an APR equipped with a HEPA filter certified by NIOSH under 30 CFR part 11 or a particulate filter certified under 42 CFR part 84; for particles with MMAD ≥ 2 micrometers, any NIOSH-certified particulate filter is acceptable, per 1910.134(d)(3)(iv)(B)–(C).

In short:

• Use HEPA or equivalent NIOSH-certified particulate filters for respirators protecting against hazardous particulates unless particles are mostly ≥2 µm, where any NIOSH particulate filter will do.

An employer may rely on atmosphere-supplying respirators for certain oxygen-deficient atmospheres if they demonstrate that, under all foreseeable conditions, the oxygen concentration can be maintained within the ranges shown in Table II for the workplace altitude, per 1910.134(d)(3)(i)(A).

OSHA clarified in the letter “Oxygen-deficient atmospheres in HVAC” that:

• All oxygen-deficient atmospheres are treated as IDLH unless the employer can demonstrate maintenance within the Table II ranges for the altitude involved.
• Use Table II altitude/O2 ranges when making that demonstration; above 8,000 ft the exception does not apply.

Employers must provide a medical evaluation to determine an employee's ability to use a respirator before the employee is fit tested or required to use the respirator in the workplace, as required by 1910.134(e)(1).

Practically, do not perform fit testing or assign respirator-required tasks until the PLHCP has evaluated the worker (via questionnaire or exam) and cleared them to wear the respirator.

The employer must identify a physician or other licensed health care professional (PLHCP) to perform medical evaluations using the medical questionnaire or an equivalent initial medical exam, and the evaluation must obtain the information requested in Sections 1 and 2, part A of Appendix C per 1910.134(e)(2)(i)–(ii).

Follow-up requirements:

• If an employee answers positively to any question 1–8 in Section 2, part A of Appendix C, or the initial exam indicates a need, the employer must provide a follow-up medical exam (1910.134(e)(3)(i)).
• The PLHCP decides what additional tests or consultations are needed to make a final determination (1910.134(e)(3)(ii)).

The medical questionnaire and exams must be administered confidentially during normal working hours or at a convenient time/place, and the employee must be given a chance to discuss results with the PLHCP, per 1910.134(e)(4)(i)–(ii).

Before the PLHCP makes a recommendation, the employer must provide supplemental information including:

• The type and weight of the respirator;
• Duration and frequency of use (including rescue/escape);
• Expected physical work effort;
• Additional protective clothing/equipment to be worn;
• Temperature and humidity extremes the employee may encounter;
• A copy of the written respirator program and the standard for the PLHCP to review (1910.134(e)(5)(i)–(iii)).

The employer may discontinue an employee's medical evaluations when the employee is no longer required to use a respirator, per 1910.134(e)(2).

In other words, if a worker no longer performs tasks that require respirator use and is not expected to use a respirator, the periodic medical evaluation requirement can end.

No — employers are not required to have employees medically re‑evaluated solely because they selected a new PLHCP. OSHA states that when an employer replaces a PLHCP, the employer must ensure the new PLHCP obtains the employee’s medical information either by providing the documents directly or by having them transferred from the former PLHCP, but OSHA does not expect reevaluation just because the PLHCP changed (Requirement in 1910.134(e)(5)(iii).

• Action steps for employers: promptly transfer or provide the PLHCP medical records needed for ongoing medical determinations; continue to follow any existing PLHCP recommendations and scheduled follow‑ups unless the new PLHCP advises otherwise.

Reference: Requirement in 1910.134(e)(5)(iii).

The PLHCP must provide a written recommendation that states whether the employee is medically able to use the respirator and only includes: any limits on respirator use related to the employee’s medical condition or workplace conditions, the need (if any) for follow‑up medical evaluations, and a statement that the employee received a copy of the PLHCP’s written recommendation (Requirement in 1910.134(e)(6)(i)(A), 1910.134(e)(6)(i)(B), 1910.134(e)(6)(i)(C).

• Practical tip: keep the PLHCP recommendation with the employee’s respirator medical record and act on any stated limitations (for example, restriction to a PAPR or restriction from certain work).

If the PLHCP finds a medical condition that may increase health risk from using a negative‑pressure respirator but finds the employee can use a powered air‑purifying respirator (PAPR), the employer must provide a PAPR. If a later medical evaluation shows the employee can use a negative‑pressure respirator, the employer may stop providing the PAPR (Requirement in 1910.134(e)(6)(ii).

• In practice: follow the PLHCP’s recommendation exactly — if it limits negative‑pressure respirator use but allows PAPRs, supply and train the employee on the PAPR until a medical reassessment allows other options.

Reference: Requirement in 1910.134(e)(6)(ii).

Additional medical evaluations must be provided when specific signs, information, observations, or workplace changes indicate they are needed. The employer must provide evaluations at minimum when an employee reports respirator‑related medical signs or symptoms; a PLHCP, supervisor, or program administrator recommends reevaluation; fit testing or program evaluations indicate a need; or workplace changes substantially increase physiological burden (e.g., heavier work, different protective clothing, temperature changes) (Requirement in 1910.134(e)(7)).

• Examples: employee complains of dizziness while wearing a respirator; a fit test shows repeated poor fit; job physical demands increase significantly — each calls for a follow‑up medical exam.

Reference: Requirement in 1910.134(e)(7).

Any negative‑ or positive‑pressure tight‑fitting facepiece respirator requires fit testing before the employee is assigned to use it, whenever a different facepiece (make, model, style, or size) is used, and at least annually thereafter (Requirement in 1910.134(f), 1910.134(f)(1), 1910.134(f)(2).

• Also required: additional fit tests when changes in physical condition (facial scarring, dental work, weight change, cosmetic surgery) could affect fit, and prompt retesting if the user reports an unacceptable fit (1910.134(f)(3), 1910.134(f)(4)).

Reference: Requirement in 1910.134(f).

QLFT may only be used to fit test negative‑pressure air‑purifying respirators that must achieve a fit factor of 100 or less; quantitative fit testing (QNFT) passes when the measured fit factor is ≥100 for tight‑fitting half facepieces or ≥500 for tight‑fitting full facepieces (1910.134(f)(6), 1910.134(f)(7)).

• Note: Fit testing of tight‑fitting atmosphere‑supplying respirators and tight‑fitting PAPRs must be done in the negative‑pressure mode using the specified methods regardless of the respirator’s operational pressure (1910.134(f)(8)).

References: 1910.134(f)(6), 1910.134(f)(7), 1910.134(f)(8).

Atmosphere‑supplying respirators and tight‑fitting PAPRs must be fit‑tested in the negative‑pressure mode: qualitatively by temporarily converting the actual facepiece to a negative‑pressure respirator or by using an identical negative‑pressure surrogate facepiece, and quantitatively by providing a means to sample inside the facepiece (permanent probe or temporary sampling adapter); any test modifications must be removed and the facepiece restored to NIOSH‑approved configuration before workplace use (1910.134(f)(8)(i), 1910.134(f)(8)(ii), 1910.134(f)(8)(iii)).

• Practical checklist: arrange a surrogate or adapter for testing, perform test in negative‑pressure mode, then fully remove adapters/probes and verify the respirator is returned to its original NIOSH‑approved configuration before issuing it for use.

Reference: 1910.134(f)(8)(i)–(iii).

Employees with facial hair that comes between the sealing surface and the face or that interferes with valve function may not wear tight‑fitting facepiece respirators, and employers must ensure corrective eyewear or other PPE do not interfere with the facepiece seal (1910.134(g)(1)(i)(A), 1910.134(g)(1)(i)(B), 1910.134(g)(1)(ii).

• What to do: if the worker needs respiratory protection but has facial hair that interferes with the seal, provide an alternative such as a PAPR with a loose‑fitting hood or helmet, or require the worker to be clean‑shaven where the sealing surface contacts the skin.
• Also require every tight‑fitting respirator user to perform a user seal check each time they don the facepiece following appendix B‑1 or equivalent manufacturer's procedures (1910.134(g)(1)(iii)).

Reference: 1910.134(g)(1)(i)(A)–(B), (g)(1)(ii), (g)(1)(iii).

Employees must leave the respirator use area to wash their faces and respirator facepieces as necessary to prevent irritation; if they detect vapor or gas breakthrough, increased breathing resistance, or facepiece leakage; or to replace the respirator or its filter, cartridge, or canister elements (1910.134(g)(2)(ii)(A), 1910.134(g)(2)(ii)(B), 1910.134(g)(2)(ii)(C)).

• Employer responsibilities: provide facilities and procedures that allow timely removal for these reasons, and ensure replacement cartridges/filters are available and properly selected for the hazard.

Reference: 1910.134(g)(2)(ii)(A)–(C).

When employees enter IDLH atmospheres the employer must ensure at least one attendant is located outside the IDLH, maintain visual/voice/signaling communication between inside and outside employees, train and equip outside employees for effective rescue, notify the employer/designee before outside personnel enter to rescue, and equip outside personnel with pressure‑demand or other positive‑pressure SCBAs or pressure‑demand supplied‑air respirators with auxiliary SCBA plus retrieval equipment or an equivalent means (1910.134(g)(3)(i)–(vi)(A)–(C)).

• Additional note on oxygen‑deficient atmospheres: where civilian employees are covered by OSHA, oxygen‑deficient atmospheres are treated as IDLH and covered by 1910.134 (see OSHA interpretation on HVAC and oxygen‑deficient atmospheres for civilian workplaces) (Oxygen‑deficient atmospheres in HVAC).

Reference: 1910.134(g)(3), and Oxygen‑deficient atmospheres in HVAC interpretation.

Respirators must be cleaned and disinfected at intervals based on their use: respirators issued for the exclusive use of one employee must be cleaned as often as necessary to remain sanitary; respirators issued to multiple employees must be cleaned before being worn by different people; emergency respirators must be cleaned after each use; and respirators used in fit testing and training must be cleaned after each use (1910.134(h)(1)(i)–(iv)).

• Employers must use the cleaning/disinfecting procedures in appendix B‑2 or manufacturer procedures that the employer demonstrates are equally effective (1910.134(h)(1)).

Reference: 1910.134(h)(1).

Employers must store respirators so they are protected from damage, contamination, sunlight, extreme temperatures, excessive moisture, and damaging chemicals, and so the facepiece and exhalation valve are not deformed. See the storage requirements in 1910.134(h)(2).

• For general storage, follow 1910.134(h)(2)(i) — keep respirators packed or stored to prevent deformation and shield them from contaminants and environmental damage.
• For emergency respirators, also follow 1910.134(h)(2)(ii): they must be kept accessible to the work area (1910.134(h)(2)(ii)(A)), stored in clearly marked compartments or covers (1910.134(h)(2)(ii)(B)), and stored in accordance with any applicable manufacturer instructions (1910.134(h)(2)(ii)(C)).

Practical tips: use dedicated, labeled cabinets or sealed containers away from sunlight and chemicals; keep emergency respirators in marked, easy-to-reach locations; and retain manufacturer storage instructions with the equipment.

Employers must inspect respirators before use or on a scheduled basis depending on their type: routine respirators are inspected before each use and during cleaning; emergency respirators are inspected at least monthly and per manufacturer recommendations and checked for proper function before and after each use; emergency escape-only respirators must be inspected before being carried into the workplace. See 1910.134(h)(3)(i).

• Required inspection checks include a test of respirator function, tightness of connections, and the condition of parts such as the facepiece, head straps, valves, connecting tube, and cartridges/canisters/filters, as well as checking elastomeric parts for pliability and signs of deterioration (1910.134(h)(3)(ii)(A) and 1910.134(h)(3)(ii)(B)).
• Self-contained breathing apparatus (SCBA) must be inspected monthly; air and oxygen cylinders must be kept fully charged and recharged when pressure falls to 90% of the manufacturer's recommended pressure, and the employer must verify that the regulator and warning devices function properly (1910.134(h)(3)(iii)).
• For respirators maintained for emergency use, employers must certify inspections by documenting date, inspector, findings, remedial actions, and an identifier for the respirator; that information must be attached to the respirator or stored with inspection records (1910.134(h)(3)(iv)(A) and 1910.134(h)(3)(iv)(B)).

Follow these checks and recordkeeping steps so defective respirators are identified and removed from service promptly.

Employers must ensure breathing gases meet high-purity specifications: compressed and liquid oxygen must meet United States Pharmacopoeia requirements for medical or breathing oxygen, and compressed breathing air must meet at least Grade D air as described in 1910.134(i)(1).

• Grade D breathing air requirements are listed in 1910.134(i)(1)(ii) and include: oxygen content 19.5–23.5% by volume (1910.134(i)(1)(ii)(A)), hydrocarbon (condensed) ≤ 5 mg/m3 (1910.134(i)(1)(ii)(B)), carbon monoxide ≤ 10 ppm (1910.134(i)(1)(ii)(C)), carbon dioxide ≤ 1000 ppm (1910.134(i)(1)(ii)(D)), and lack of noticeable odor (1910.134(i)(1)(ii)(E)).
• Cylinders of purchased breathing air must meet DOT testing and maintenance rules (1910.134(i)(4)(i)), come with a supplier certificate of analysis (1910.134(i)(4)(ii)), and have moisture content not exceeding a dew point of −50 °F at 1 atm (1910.134(i)(4)(iii)).
• Compressors must be designed and located to prevent entry of contaminated air, minimize moisture (dew point at least 10°F below ambient), and include suitable in-line sorbent beds and filters maintained per the manufacturer (1910.134(i)(5) and its subparts). The compressor must carry a tag with the most recent change date and authorized signature (1910.134(i)(5)(iv)).
• Carbon monoxide limits and monitoring: non–oil-lubricated compressors must keep CO ≤ 10 ppm (1910.134(i)(6)); oil-lubricated compressors must use high-temperature or carbon-monoxide alarms (or both) and monitor the air supply at intervals sufficient to prevent CO exceeding 10 ppm (1910.134(i)(7)).
• Additional controls: couplings for breathing air must be incompatible with nonrespirable outlets and no asphyxiating substance may be introduced; use only NIOSH‑approved breathing-gas containers per the NIOSH approval (1910.134(i)(8) and 1910.134(i)(9)).

Note: OSHA treats atmospheres with oxygen below 19.5% by volume as oxygen-deficient and immediately dangerous to life or health (IDLH) in many contexts; see OSHA’s Letter of Interpretation on oxygen-deficient atmospheres for discussion of the 19.5% threshold and applicability to covered civilian employees (OSHA interpretation on oxygen-deficient atmospheres).