Respiratory protective devices (respirators) fall into two main categories based on facial coverage:

  • Half Face Respirator: Covers the nose, mouth, and chin only; does not protect the eyes.
  • Full Face Respirator: Covers the entire face, including the eyes, providing additional protection against irritant gases and splashes.

Both types work on the same principle of removable, replaceable filters/cartridges. The main difference between them is the area of facial coverage, not the filter type itself. The filter or cartridge is selected based on the contaminant present in the work environment (dust, organic vapors, acid gases, ammonia, etc.), regardless of whether the mask is half face or full face — provided the connector (bayonet/thread) is compatible.

First : Types of Filters and Cartridges
1- Particulate Filters

These work by mechanical filtration to capture solid and liquid particles suspended in the air, such as dust, fumes, mist, and microorganisms. They provide no protection whatsoever against gases or chemical vapors.

2- Gas / Vapor Cartridges

These contain activated carbon (sometimes with added chemical impregnations) that chemically adsorbs gas or vapor molecules. Each type is designed for a specific family of chemicals (organic, acidic, ammonia, etc.) and provides no protection against solid particles.

3- Combined Filters

These combine a particulate filtration layer with a chemical adsorption layer for gases in a single cartridge. They are used when both hazards (gases + particles) are present simultaneously, such as during spray painting operations.

Second : Particulate Filter Classification and Meaning
Class (EN 143) Filtration Efficiency US Equivalent (NIOSH) Typical Use
P1 ≥ 80% N95 (approx.) Wood dust, non-toxic dust
P2 ≥ 94% N95 / N99 Metal dust, mist, some solid fumes
P3 ≥ 99.95% N100 / P100 Highly toxic particles, asbestos, fine chemical mist

The standard color for particulate filters (per EN 14387) is white; an additional color is added when combined with a gas filter (combined filter).

Third : Gas & Vapor Filter Classification and Meaning
Code Standard Color Type of Protection / Target Gases
A Brown Organic gases and vapors (boiling point above 65°C) — solvents, paints, benzene
B Grey Inorganic gases and vapors — chlorine, hydrogen cyanide, hydrogen sulfide
E Yellow Acid gases — sulfur dioxide, hydrochloric acid
K Green Ammonia and its organic derivatives (amines)
AX Brown (striped) Low-boiling organic vapors (below 65°C) — for short-term use only
Hg Red/Orange Mercury vapor (typically used with P3, for a limited time only)
CO — Carbon monoxide — a very specialized filter, uncommon, and limited in use
NO Light Blue Nitrogen oxides
P White Solid/liquid particles (combined with any of the above codes to form a combined filter)

A combined filter such as ABEK-P3 provides comprehensive protection against the four main gas types (A+B+E+K) plus the highest particulate filtration efficiency (P3), and is typically used in industrial environments where the hazard type is unspecified or high-risk.

Fourth : Capacity Classes (Class 1, 2, 3) and Meaning

Each gas code (A, B, E, K…) has three capacity classes. The difference between them is the duration of protection (breakthrough time), not the type of protection:

Class Capacity Typical Use
Class 1 Low capacity Low contaminant concentrations, lower breathing resistance (more comfortable)
Class 2 Medium capacity The most common general industrial use
Class 3 High capacity High concentrations or long exposure periods, higher breathing resistance

Note: Increasing the class (from 1 to 3) does not mean “stronger” protection against a different type of gas — it means greater adsorption capacity for the same gas type, i.e., a longer usable duration before saturation.

Fifth : Other Technical Specifications and Their Meaning
  • Filtration Efficiency (%): The percentage of particles the filter stops out of the total particles in the tested air.
  • Breathing Resistance / Pressure Drop: Resistance to airflow through the filter during inhalation and exhalation; higher efficiency or capacity class generally increases resistance, reducing breathing comfort.
  • Breakthrough Time: The time it takes for a gas to reach a specified concentration behind the filter, used to determine the cartridge’s usable service life.
  • Connection Type: Either a manufacturer-specific bayonet fitting, or a standard 40mm thread per EN 148-1, which allows filters from different brands to be used on the same mask.
  • ESLI (End of Service Life Indicator): Some advanced cartridges (especially for specific gases like formaldehyde) include a color indicator that changes as saturation approaches.
  • Shelf Life: The lifespan of an unused, sealed filter (typically 3–5 years), distinct from the actual in-use service life after opening.
  • Weight and Mask Size: Affect comfort during extended use, particularly with full face respirators.
Important Notes and Warnings
  • Never use any particulate or chemical filter in oxygen-deficient environments (below 19.5%); a self-contained breathing apparatus (SCBA) must be used instead.
  • A particulate filter alone does not protect against gases, and a gas filter alone does not protect against particles; a combined filter must be selected when both hazards are present together.
  • Always match the filter’s code and class to the actual contaminant listed in the Safety Data Sheet (SDS/MSDS) for the chemical in use.
  • A filter with an EN 148-1 thread connector cannot be fitted to a bayonet-connector mask, or vice versa; verify connector compatibility before purchase.
  • Replace the filter immediately if you smell or taste the contaminant, experience difficulty breathing, or when the manufacturer’s recommended service life is reached — whichever comes first.