1.2 Knowing the air: hazard evaluation, IDLH and oxygen

1 The four general selection requirements

Paragraph (d)(1) sets four rules that apply before any specific respirator is chosen.

1. 1
   (d)(1)(i) — select and provide an appropriate respirator based on the respiratory hazard(s) to which the worker is exposed and on workplace and user factors that affect respirator performance and reliability.
2. 2
   (d)(1)(ii) — select a NIOSH-certified respirator, used in compliance with the conditions of its certification.
3. 3
   (d)(1)(iii) — identify and evaluate the respiratory hazards, including a reasonable estimate of employee exposures and an identification of the contaminant's chemical state and physical form. Where the employer cannot identify or reasonably estimate the exposure, the atmosphere shall be considered IDLH.
4. 4
   (d)(1)(iv) — select from a sufficient number of respirator models and sizes so that the respirator is acceptable to, and correctly fits, the user.

The phrase chemical state and physical form in (d)(1)(iii) is doing quiet work. A particulate needs a filter; a gas or vapor needs a sorbent cartridge; something that is both needs a combination. Getting the physical form wrong is how a crew ends up wearing P100 filters against a solvent vapor that walks straight through them.

2 A reasonable estimate of exposure

The standard asks for a reasonable estimate, not necessarily a personal sample for every worker. Several routes get you there, and which ones are available depends on the substance.

Where a substance-specific standard applies, it will usually spell out the method. 1926.1153(d)(2) gives silica work two named routes — a performance option based on any combination of air monitoring data or objective data, and a scheduled monitoring option based on personal breathing zone samples. Table 1 of that standard offers a third path: implement the specified controls fully and properly, and the required respirator is given to you without an assessment. 1926.62(d)(2) does something different again for lead, presuming a set of listed tasks to be above the limit until an assessment shows otherwise.

Where no substance-specific standard applies, the comparison points are the permissible exposure limits in 29 CFR 1910.1000 for general industry and 29 CFR 1926.55 for construction, and the exposure limits printed in section 8 of the safety data sheet.

3 IDLH: what it means and what it demands

Paragraph (b) defines immediately dangerous to life or health (IDLH) as an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere.

That third limb is the one that catches people. An atmosphere can be IDLH not because it kills quickly but because it makes you unable to walk out — disorientation, narcosis, loss of coordination. A worker who cannot self-rescue is in an IDLH atmosphere regardless of what the concentration would do over eight hours.

For IDLH atmospheres, paragraph (d)(2)(i) allows only two options: a full facepiece pressure demand SCBA certified by NIOSH for a minimum service life of thirty minutes, or a combination full facepiece pressure demand supplied-air respirator with auxiliary self-contained air supply. Nothing else. An air-purifying respirator is never acceptable in an IDLH atmosphere, and paragraph (d)(3)(i)(B)(2) reinforces the point from the other direction: employers must not apply maximum use concentrations to IDLH conditions.

Escape-only respirators are treated separately: (d)(2)(ii) requires respirators provided only for escape from IDLH atmospheres to be NIOSH-certified for escape from the atmosphere in which they will be used.

4 Oxygen deficiency

Paragraph (b) defines an oxygen deficient atmosphere as an atmosphere with an oxygen content below 19.5% by volume. Paragraph (d)(2)(iii) then states that all oxygen-deficient atmospheres shall be considered IDLH.

There is one narrow exception, and it is worth stating precisely because it is often misremembered as a general permission. If the employer demonstrates that, under all foreseeable conditions, the oxygen concentration can be maintained within the ranges specified in Table II of the section — which sets those ranges by altitude — then any atmosphere-supplying respirator may be used. Note what that permits: an atmosphere-supplying respirator, not an air-purifying one. A filter still cannot make oxygen.

This is the point where respiratory protection and confined space work meet. A space that is oxygen deficient is IDLH here and is a hazardous atmosphere under 29 CFR 1910.146; the entry rules, attendant, rescue arrangements and atmospheric testing of that standard apply alongside everything in this one.

5 Gases and vapors: the service life problem

A particulate filter loads up and gets harder to breathe through — the wearer notices. A gas or vapor cartridge does not: it simply stops adsorbing, and the contaminant passes through with no change in breathing resistance and, for many substances, no smell.

Paragraph (d)(3)(iii) deals with this. For protection against gases and vapors the employer shall provide either an atmosphere-supplying respirator, or an air-purifying respirator provided that it is equipped with an end-of-service-life indicator (ESLI) certified by NIOSH for the contaminant; or, if there is no appropriate ESLI, the employer implements a change schedule for canisters and cartridges based on objective information or data that will ensure they are changed before the end of their service life.

The last sentence of that paragraph is the one auditors read: the employer shall describe in the respirator program the information and data relied upon and the basis for the canister and cartridge change schedule and the basis for reliance on the data. A change schedule is not “every Friday”; it is a documented calculation or a manufacturer's tool, written into the program.

6 Workplace and user factors

Paragraph (d)(1)(i) requires selection to account not only for the hazard but for workplace and user factors that affect respirator performance and reliability. Those factors decide whether a technically correct choice survives a shift.

Work rate. Heavy work through a negative-pressure respirator adds real breathing resistance, and it is one of the things the medical evaluation in Part 3 is designed to assess.

Heat. A facepiece adds heat load. On a hot day, respirator use and heat stress interact, and the crew will take the mask off to breathe if nothing else changes.

Other PPE. Paragraph (g)(1)(ii) requires that corrective glasses, goggles or other protective equipment be worn in a manner that does not interfere with the seal. Hard hat suspension, hearing protection, welding helmets and face shields all compete for the same face and head.

Communication. If a crew cannot hear each other, they will lift the facepiece to talk. That is a selection problem, not a discipline problem, and it is exactly the kind of thing (l)(2)(i) means when it asks program evaluation to assess fit including the ability to use the respirator without interfering with effective workplace performance.