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Respiratory Filter Classes: Making the Right Selection

Your lungs are vital to your health - if hazardous particles reach the lungs they can damage the delicate tissue and cause illness. Your body has some natural defences against airborne particulate hazards but if the contaminant is in a large enough quantity and/or made up of very small particles, these defences may be overcome, resulting in ill health and increased risk of diseases such as occupational asthma, pulmonary fibrosis and cancer.

Gases and vapours are other types of respiratory hazards. As they mix readily with the air we breathe, gases and vapours are readily inhaled and may cause direct damage to the lung tissue. Other types (e.g. solvents, pesticides, mercury) can enter the bloodstream via the lungs and can then be transported around the body where they can damage organs like the liver kidneys and effect the central nervous system and at high concertrations can be lethal.

FILTER CLASSES AND SELECTION

Under the Standard AS/NZS 1716, filters used in respirators are required to meet certain performance levels to achieve a classification – this then allows determination of its suitability for use against specific contaminants at various concentrations as explained in AS/NZS 1715.

PARTICLE FILTERS

Filters are tested fhr capture efficiency in the laboratory using a salt aerosol challenge agent. Under specified test conditions, the amount of these particles that break through the filter is measured which allows classification of the filter. Under the Standard AS/NZS 1716, there are three classes of particle filters.

P1

Used for mechanically generated particulates including dusts, mists, flour and silica. This class of filter is suitable for relatively large particles (>1 micron) released in mechanical operations such as sanding, drilling, cutting, sawing and crushing.

P2

Used for mechanically and thermally generated particles like welding fumes. This class of filters has a higher capture efficiency to be able to effectively filter the many sub-micron sized thermally generated particles. The P2 is also the class of filter recommended for specific infection control applications including H1N1 Influenza 09 (Human Swine Influenza), Tuberculosis (TB) or other infectious diseases, where they can capture biologically active airborne particles and aerosols under specified conditions.

P3

Used for mechanically and thermally generated sub-micron particulates, viruses, bacteria and highly toxic materials including Beryllium and radioactive particles. A P3 filter offers higher protection than a P2 filter however this is only achieved when the P3 filter is used in combination with a full face respirator.

GAS & VAPOUR FILTERS

Gas/Vapour filters are produced specifically for use against various gases and vapours and are tested and marked accordingly. AS/NZS 1716 uses a code/colour classification system to identify the different types of contaminants these treated carbon grains will capture.

 CLASS 

 COLOUR 

 APPLICATION

 A

Brown

Organic vapours with boiling points > 65C

AX 

Brown 

Organic vapours with boiling points < 65C

Grey 

Inorganic gases 

Yellow 

Acid gases 

Green 

Ammonia 

Hg 

Red 

Mercury 

Brown 

Organic compounds with low vapour pressure 


All gas/vapour filters are also rated for their absorptive capacity. In increasing capactiy there are Class Aus, Class 1, Class 2 and Class 3 filter. The higher the class, the higher and longer the concentrations they are able to deal with when fitted on the right types of respirator. By combining the two types of filters (particle and gas and vapour), we can get combination filters like A1P2, BAus1 or A2B2E2K1P3.

 
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