PPE / Respirator Advisor
Jurisdiction
What do these lines mean?
Health limit — the NIOSH Recommended Exposure Limit (REL), a health-based recommendation. NIOSH has no regulatory authority; the REL is advisory only.
Legal limit— the OSHA Permissible Exposure Limit (PEL), the legally enforceable limit under 29 CFR 1910. Many PELs date to OSHA's original 1971 adoption and have not been updated since.
Danger line — the NIOSH Immediately Dangerous to Life or Health (IDLH) value: the concentration above which an escape-only respirator (or worse) is the only acceptable protection strategy.
Read before you use this
Screening aid, not a substitute for exposure assessment by a qualified industrial hygienist. Always confirm against the primary standard before making a respiratory-protection decision.
US: 681 substances (NIOSH Pocket Guide to Chemical Hazards). EU: 237 substances (EU OEL directives).
Reference only. Not legal or regulatory advice. Verify against the primary source before you act.
How it works
Pick a jurisdiction, search for a substance by name or CAS number, and enter a measured airborne concentration. The scale plots that concentration against the substance's published exposure limits: for the US, the NIOSH Recommended Exposure Limit (REL, "Health limit"), the OSHA Permissible Exposure Limit (PEL, "Legal limit"), and the Immediately Dangerous to Life or Health value (IDLH, "Danger line"); for the EU, the Indicative Occupational Exposure Limit Value (IOELV, "Health limit") and, where one exists, the Binding Occupational Exposure Limit Value (BOELV, "Legal limit") under the Carcinogens, Mutagens and Reproductive Toxicants Directive.
Some substances have no numeric limit to plot — a NIOSH carcinogen (Ca) designation with no REL value, for example, or a substance measured only in fibers/cm³ — and the tool says so plainly rather than guessing or showing a misleading number.
Canada is not yet available. This is a screening aid, not a substitute for exposure assessment by a qualified industrial hygienist.
Worked example
Acetone (US), measured at 1,200 ppm: Health limit (REL) 250 ppm, Legal limit (PEL) 1,000 ppm, Danger line (IDLH) 2,500 ppm. 1,200 ppm sits above the legal limit and below the danger line.
Acetaldehyde (US) carries a NIOSH carcinogen (Ca) designation with no numeric REL — the tool shows the carcinogen advisory instead of a Health-limit line, while the PEL and IDLH lines still render normally.
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last updated 2026-07-30