Reference

OSHA permissible exposure limits live in three separate tables that work three different ways, and 29 CFR 1910.1000(d) supplies the arithmetic for deciding whether a measured exposure is over the limit. This guide works both formulae with real numbers, decodes the ceiling and peak columns, and explains why most PELs date from 1971.

Respiratory protective equipment (RPE) is the umbrella term for every device that protects breathing — from disposable N95s and FFP3s to powered and supplied-air systems. This guide maps the full family tree, the adequate-and-suitable selection test, fit testing rules, and how the US, UK, EU, Canadian, and Australian rulebooks attach.

Assigned protection factors differ by country: OSHA credits every half mask 10, the UK runs a 4/10/20/40 ladder, EN 529 defines nominal factors with national APFs beneath, and Australia gates P3 to full facepieces. One master table, the three cross-border traps, and a four-jurisdiction worked selection example.

CSA Z94.4 is Canada's respirator standard — a selection, use, and care program built on NIOSH-certified equipment. This guide covers the 2018 edition, the two-year fit-testing cycle, provincial enforcement from WorkSafeBC to Ontario, wildfire-smoke selection against the AQHI, and a worked example for a silica-exposed BC crew.

Assigned protection factors (APF) are the protection levels OSHA assigns to each respirator class in 29 CFR 1910.134 Table 1. This guide decodes the APF table from quarter mask to pressure-demand SCBA, shows how APF and the exposure limit set the maximum use concentration, and works an example of picking a respirator from a measured exposure.

Choosing a half mask respirator means matching the mask to your hazard, your face, and the cartridges you need - not just grabbing a popular model. This guide covers the assigned protection factor, elastomeric vs disposable, sizing, cartridge compatibility, the mandatory fit test, and the major brand series side by side.

Most OSHA PELs derive from 1968 ACGIH TLVs and have not been updated since 1971 — ACGIH updates TLVs annually. For many chemicals the TLV is 5–20× lower than the PEL, requiring a higher APF respirator. ANSI/ASSP Z88.2 directs employers to use the most protective OEL. This guide covers the practical selection implications.

ANSI/ASSP Z88.2 is the consensus respiratory protection program standard, providing guidance that goes beyond OSHA 1910.134 minimums. It covers hazard identification, respirator selection, written programs, fit testing, and program evaluation. This guide explains Z88.2's structure and how it relates to 1910.134 and NIOSH 42 CFR Part 84.