In this module
Objectives covered: LO 1.5.1. By the end you will be able to:
- Identify airborne hazards and oxygen-deficient atmospheres.
- Tell the difference between air-purifying and air-supplying respirators.
- Use assigned protection factors (APF) to choose a respirator.
- Explain why medical checks, fit testing and seal checks are needed.
5.1 Airborne hazards
- Dust: solid particles from crushing, grinding, cutting (cement, silica, cotton, flour).
- Fume: very fine metal particles from welding and hot cutting.
- Mist: liquid droplets from spraying, plating, cleaning.
- Gas and vapour: ammonia, chlorine, hydrogen sulphide, solvents.
- Oxygen deficiency: air with less than 19.5% oxygen, common in tanks, ship hulls, pits and other confined spaces.
5.2 The respiratory protection programme
When respirators are required, OSHA 29 CFR 1910.134 requires a written programme run by a trained programme administrator. It must cover:
- respirator selection based on the hazard and its concentration,
- a medical evaluation before fit testing and use,
- fit testing for every tight-fitting respirator,
- procedures for use, cleaning, storage, repair and cartridge change,
- air quality for supplied-air systems, and
- training and regular programme evaluation.
5.3 Types of respirator
| Type | How it works | Typical use |
|---|---|---|
| Filtering facepiece (N95, FFP2) | The whole mask is the filter | Nuisance and moderate dust |
| Half-mask with filters or cartridges | Rubber or silicone mask, replaceable filters | Dust, fume, low gas and vapour levels |
| Full-facepiece air-purifying | Covers eyes too, better seal | Higher levels, eye irritants such as ammonia |
| Powered air-purifying (PAPR) | Battery blower pushes filtered air in | Long shifts, hot conditions, people with beards (loose hood) |
| Supplied-air (airline) | Clean air through a hose from a compressor | Painting, abrasive blasting, long tank work |
| Self-contained breathing apparatus (SCBA) | Worker carries an air cylinder | Oxygen deficiency, unknown or IDLH atmospheres, rescue |
Air-purifying respirators clean the air; they do not add oxygen. Never use them in oxygen-deficient or IDLH (immediately dangerous to life or health) atmospheres. Use SCBA, or an airline respirator with an escape cylinder.
5.4 Assigned protection factors
The APF tells you how much a respirator reduces the exposure when used correctly in a full programme. The figures below are from OSHA 1910.134(d)(3)(i)(A), Table 1.
| Respirator | APF |
|---|---|
| Filtering facepiece or elastomeric half mask | 10 |
| Loose-fitting PAPR hood or helmet | 25 |
| Full-facepiece air-purifying | 50 |
| Full-facepiece PAPR | 1,000 |
| SCBA, pressure-demand, full facepiece | 10,000 |
Maximum use concentration (MUC) = APF × exposure limit. Example: a dust has an exposure limit of 5 mg/m³. A half mask (APF 10) can be used up to 10 × 5 = 50 mg/m³. If air sampling shows 120 mg/m³, you need a full facepiece (APF 50, MUC 250 mg/m³) or better.
5.5 Filters and cartridges
- Particle filters (NIOSH): N = not oil-resistant, R = oil-resistant, P = oil-proof; 95, 99 or 100 = percent efficiency. P100 filters are magenta.
- Gas and vapour cartridges (NIOSH colour codes): organic vapour = black, acid gas = white, ammonia/methylamine = green.
- European codes (EN 14387): A = organic (brown), B = inorganic such as chlorine (grey), E = acid gas (yellow), K = ammonia (green), P = particles (white, P1 to P3).
- Change gas cartridges on a fixed schedule worked out from the maker's data. Do not wait to smell the chemical.
5.6 Medical checks, fit testing and seal checks
- A medical evaluation confirms the worker can breathe safely through a respirator.
- A fit test is required before first use, whenever a different model or size is used, at least annually, and when the worker's face changes (weight change, dental work, scars) (1910.134(f)).
- Fit tests can be qualitative (taste or smell test with saccharin or Bitrex) or quantitative (instrument measures leakage).
- Do a user seal check every time you put the respirator on: cover the inlets and breathe in (the mask should pull in), cover the outlet and breathe out (the mask should bulge).
- Beards and stubble where the mask seals will break the seal. Tight-fitting respirators need a clean-shaven seal area.
In a urea fertiliser plant, ammonia leaks can happen at pump seals and flanges. Operators carry a full-face mask with green ammonia (K) cartridges for escape only. Leak repair or entry into an unknown concentration is done with SCBA by a trained team. In a cement grinding unit, packers handling bags wear fit-tested FFP2/N95 respirators. The plant also fitted dust extraction at the packing machine so that the respirator is backup protection, not the main control.
Learning Check
Answer these two questions to check your understanding. You can try again as many times as you like.