- A dust mask does nothing against solvent vapour. You need a vapour filter, marked with the letter A.
- For one-pack engine paint, a well-fitting half mask with A2P3 filters is the usual choice.
- A beard breaks the seal. So does a mask that was never checked for fit.
- For two-pack (2K) paint HSE accepts only air-fed breathing apparatus. No filter qualifies.
- The battery-powered "air fed" masks sold online are filter masks with a fan. They are not breathing apparatus.
Dust, vapour and mist
Spraying paint puts two things in the air. One is a mist of fine droplets, which is a particle hazard. The other is solvent vapour, which is a gas. A paper dust mask stops some of the first and none of the second.
Filters for reusable masks are marked for both. The letter A means the filter absorbs organic vapours, which covers paint solvents. The number after it is capacity: A1 is low and A2 is medium, so an A2 filter lasts longer before the solvent breaks through. P is for particles, and P3 is the highest grade. An A2P3 filter handles both the vapour and the mist from one-pack paint, which is why it is the standard recommendation for spraying solvent paints.
An A1P2 mask is adequate for an occasional aerosol outdoors. For a gun, or for regular work, buy A2P3.
Fit matters more than the filter
A filter only works on the air that passes through it. Any gap at the edge of the mask lets unfiltered air in, and it takes the easy route.
Facial hair under the seal defeats a half mask. So does the wrong size. In workplaces, HSE requires a fit test for any mask that seals to the face, and the reason holds at home. Do the check the maker describes every time you put it on: cover the filters, breathe in gently, and the mask should pull onto your face and stay there.
Vapour filters wear out. Change them by the maker's schedule, or at once if you can smell or taste solvent through the mask. Between uses, keep the mask in a sealed bag or box. A filter left out in the garage goes on absorbing fumes until it is spent.
Add eye protection that seals, nitrile gloves and a hooded disposable coverall. Solvent and paint get into you through skin as well.
Why two-pack is different
The hardener in two-pack paint contains isocyanates. The safety page explains what they do. The point here is what stops them.
HSE's position has no exceptions: "Filtering respirators are not suitable for spraying isocyanate paints. The respiratory protective equipment (RPE) must be air-fed breathing apparatus."
Air-fed means clean air arrives down a hose from somewhere outside the spray area, in enough volume that the inside of the visor or mask stays at positive pressure. Mist can't leak in because air is always flowing out. HSE's leaflet describes the acceptable types as "visor-type, air-fed BA with a low-flow indicator, or half-mask BA (with constant airflow supply)". The standard is BS EN 14594, with an assigned protection factor of at least 20.
The air itself has to be fit to breathe. HSE says it "should be uncontaminated and in sufficient quantity to protect the user". A workshop compressor puts oil mist, water and sometimes carbon monoxide into its air, so a breathing air supply needs its own filtration, and the compressor's intake has to be somewhere the paint mist can't reach.
The apparatus stays on through the whole clearance time of the booth, and HSE warns specifically against lifting the visor to look at the work.
The "air fed" masks sold online
Search a marketplace for an air-fed mask and most of what comes up is a full-face mask with a battery fan and screw-in carbon filters. These are powered filtering respirators. The fan makes them more comfortable to breathe through, and they still clean the air around you with a filter. HSE's sentence about filtering respirators applies to them exactly as it does to a half mask.
Real air-fed equipment comes from paint trade suppliers, from makers such as DeVilbiss, SATA and 3M, and it arrives with a certificate to BS EN 14594 and a specification for the air supply. Expect to pay several hundred pounds for the mask, belt regulator, hose and filtration. We don't list any in the shop, because we couldn't confirm the standard for anything a general retailer sells.
If that outlay doesn't make sense for one engine, a bodyshop will spray your parts in two-pack for you.
See the filter masks and coveralls in the shop.
Sources
- HSE: types of RPE for spraying: filtering respirators unsuitable, air-fed apparatus, protection factor, fit testing
- HSE INDG388: safety in isocyanate paint spraying: acceptable types of breathing apparatus, air quality, never lifting the visor
- HSE: respiratory protective equipment at work (HSG53): how to select, fit and look after a respirator