Dust Masks Terminology

Particle filters
Particle filters trap and hold particles (dust, mist, fume, smoke, micro-organisms) from the air flowing through them. Large particles are easier to trap than small ones. These filters can be used against both solid particles and liquid particles (mists, fine sprays and aerosols).

Solid particulate (particles of solid material, including aerosols, dusts, fibres, smokes and fume) examples:

  • Asbestos dust
  • Engine exhaust particles and fume
  • Lead dust and fume
  • Stone dust
  • Welding fume
  • Wood dust
  • Smoke
  • Fungal spores and parasites
  • Bacteria and viruses
  • Flour

Liquid particulate (fine sprays, mists and aerosols made up of small droplets of liquid) examples:
Sprayed liquids:

  • paints
  • pesticides
  • powder coating mix
  • liquid jetting


  • chrome acid
  • cutting fluids
  • oil mists

Particle filters do not trap gases or vapours, or give any protection against oxygen-deficient atmospheres.

Particle filters are classified according to their efficiency. The filter (or the facepiece it is built into) will be marked with the letter P (for particle) and a number to indicate efficiency, or the level of protection provided.

  • P1 = Low efficiency.
  • P2 = Medium efficiency.
  • P3 = High efficiency.

Particulate filters are additionally marked:

  • NR = Not reusable – Designed for a single work shift (eight hours) and must be disposed of safely at the end.
  • R = Reusable.

Change when filters are damaged or visibly contaminated. Change when they become harder to breathe through. This can happen quickly if the wearer is exposed to very high dust concentrations.

Gas/vapour filters
These filters are designed to remove gases or vapours as specified by the manufacturer.

Gas/vapour filters do not protect against particles, or give any protection against oxygen-deficient atmospheres.

Gas/vapour filters are classified according to their capacity and the type of substance they can be used against. Their capacity refers to how much of the specified contaminant they can hold(as measured in a laboratory test at set conditions):

  • Class 1 = Low capacity.
  • Class 2 = Medium capacity.
  • Class 3 = High capacity.

Respirator standards
BS EN 136:1998 – Full face masks. Requirements, testing, marking.
BS EN 143:2000 + A1:2006 – Particle filters. Requirements, testing, marking
BS EN 149:2001+A1:2009 – Filtering half masks to protect against particles. Requirements, testing, marking.
BS EN 14387:2004+A1:2008 – Gas filter(s) and combined filter(s). Requirements, testing, marking.

Respirator abbreviations
APF Assigned Protection Factor
BA Breathing Apparatus
CE Conformite Europeene
Passed dolomite clogging test
FFP Filtering Facepiece- number indicates filter type
FF Fit Factor
HEPA High Efficiency Particulate Air
NR Non-reusable
NPF Nominal Protection Factor
PAPR Powered Air Purifying Respirator
R Reusable
RPD Respiratory Protective Device
RPE Respiratory Protective Equipment
PPE Personal Protective Equipment
SCBA Self Contained Breathing Apparatus
TH Turbo Hood
WPF Workplace Protection Factor