Personal Protective Equipment - PPE

Filter selection guide

Filter selection guide

Filter Selection Guide for Dräger respiratory masks

Here we will give you a brief over view of the most important factors to consider when choosing filtering respiratory protection devices. This information can help you protect yourself against harmful substances in the air by selecting the appropriate masks and filters.

1. What must I consider when choosing a respirator?

The hazards in your environment must be known, as well as the work requirements and the external conditions. Additionally you must take into consideration the protection level required by your respirator – as
well as the type and protection level of the necessary filter.

2. Please check the following before using filtering respiratory protection:

• Is there enough oxygen in the ambient air? (see your local legislative requirements – in Germany a
  minimum of 17 vol. % is required)
• What contaminants are in the ambient air?
• What are the concentrations of the contaminants?
• Are the contaminants in gas, particle, or vapour form? Or are they a mixture?
• Do the contaminants have adequate warning properties (e.g. smell or taste?)
• What are the applicable Occupational Exposure Limits (OEL)?
• In addition to respiratory protection, is other personal protection equipment (e.g. eye or ear protection)

3. Which respirator should I choose?

It is necessary to answer all of the above questions (in 2.) to determine the needed protection factor.
Table 1 gives you a brief overview of the nominal protection factors (NFP) for respiratory protective devices.
The NFP is the highest permissible leakage level according to the approval requirements of the
respective device. It indicates the mathmetically calculated maximum protection performance. To evaluate
the minimum required protection factor – you will need to know the concentration of the hazardous
substance you are dealing with as well as the assigned Occupational Exposure Limit (OEL) of the substance. An OEL (like AGW) is the concentration of a specific airborne substance – averaged over a
reference period, which shows no evidence to be threatening to ones health if exposed to it, at that
concentration, on a daily basis. 

List of respiratory protection devices






























Determining the needed protection factor









You can see in table 1 that with a needed minimum protection factor of 30 for lead dust, you will need to use a P3-filter or together with a half mask, a full face mask, or PAPR. In the case where the contaminants are present in both particle and gas form, the nominal protection factor must be established for each one separately. 

For the selection of filtering devices, the higher protection factor must be applied. The concentration of gases
is measured in ppm (parts per million= volume of the substance within 1 m3 of air) or mg/m3 (= weight of the
substance within 1 m3 of air) and the concentration of particles (dust) only in mg/m3. While mg/m3 deals with weight and ppm with volume, there is no direct calculation for mg/m3 to ppm. Higher concentrations are often indicated in % by volume, 10,000 ppm = 1 vol. %.

4. What is the maximum concentration of the contaminant for which I can use respiratory protection?

You can determine the maximum permissible concentration by multiplying the nominal protection factor (as
found in table 1) by the Occupational Exposure Limit (OEL).

Maximum permissible concentration = nominal protection factor x OEL

Example: Determining the maximum permissible concentration 2)

Contaminant: Chlorine dioxide
OEL: 0.1 ppm (Occupational Exposure Limit)
Respirator: Full face mask with combination filter B P2

Nominal protection factor x OEL = Maximum permissible concentration

Nominal protection factor of full face mask with gas filter: 2000 2000 x 0.1 = 200 ppm Chlorine dioxide

Nominal protection factor of full face mask with particle filter P2: 16 16 x 0.1 = 1.6 ppm Chlorine dioxide

When using a combination filter, which is the case in the above illustration, both of the maximum permissible concentrations need to be calculated, i.e. the value for the gas filter and the value for the particle filter. The lower of the two values should be taken as the maximum permissible concentration for this combination filter.
For the example above therefore, the maximum permissible concentration for chorine dioxide when using a full face mask with a B P2 combination filter is 1.6 ppm of Chlorine Dioxide 

2) Values and terms of calculation have been taken from the EN529:2005 and BGR 190. Additional national and local regulations must be followed. Values of OEL based on AGW according to German regulations and there of time-weighted average values over a reference period and not any short term exposure limits.

5. How to select the right filter?

Contaminants come in different forms – generally: aerosols (solids/particles) and gases (gases, vapours).
You can choose between the filter types to protect against one of these forms or a combination of both
of them. 

Solids / particles:            Dusts, fibres, fumes, microorganisms (e.g. viruses, bacteria, fungi,
                                          spores) and mists

Gaseous substances:     Gases and vapours 

The following table shows you the color coding of filters according to EN14387 – which helps you to
determine which filter-type is needed for the contaminants you are dealing with.

Colour coding of filters


























Differentiation of filter types:

Filters are split in different classes according to their capacity (gas filters) or their efficiency (particle filters), see table 3.

Gas filters of class 2 may be used at higher concentrations or for a longer time than class 1 filters.

The class of a particle filter indicates how efficient the filter is in filtering out particles. (class 1: 80%, class 2: 94%, class 3: 99.95%).

Differentiation of filter types




























Example for a filter type





A filter with the above mentioned colour code is suitable for the following contaminants: 

A -> gases and vapours of organic compounds with a boiling point beyond 65 °C up to concentrations
covered by filter class 2 and 

B -> inorganic gases and vapours, e.g. chlorine, hydrogen sulphide, hydrogen cyanide, up to concentrations
covered by filter class 2 and

P -> particles up to concentrations covered by filter class 3.

6. When using filtering respiratory protection, always keep the following in mind:

Never use any kind of filtering respiratory protection device . . .

• in oxygen deficient atmospheres (see local legislation for further guidelines
   e.g. Germany less than 17 vol. % O2)
• in poorly ventilated areas or confined spaces, such as tanks, small rooms, tunnels, or vessels
• in atmospheres where the concentrations of the toxic contaminants are unknown
• when the concentration of a contaminant is higher than the maximum permissible concentration and /
  or the filter class capacity
• when the contaminant has poor or no warning properties (smell, taste or irritation), such as aniline,
 benzene, carbon monoxide, and ozone 

Immediately leave the area if . . .

• breathing resistance increases noticeably
• you began to feel dizzy
• you smell, taste, or become irritated by the contaminant
• your respirator is damaged 

Make sure that . . .

• the selected respirator fits properly
• if both gases and particles are present, that you use a combination filter, to filter out both gases and particles

7. How long does a filter last?

The service life of a respiratory filter depends on its size and on the conditions of use.

Factors affecting service life:
• concentration of the con taminants
• combination of the contaminants
• air humidity
• temperature
• duration of use
• breathing rate of the user

Since the service life is influenced by many factors, it is not possible to give an estimated service life.
Important is: local / company regulations 

The end of service life is generally recognizable by:

• in gas filters by a noticeable taste or smell of the contaminant
• in particle filters by an increased breathing resistance
• in combination filters a noticeable taste or smell and/or an increased breathing resistance

Examples of contaminants, their OELs (here: AGWs, valid in Germany) and filter recommendations you can find in the printform of the DrägerFilter selection guide. Please go to the download-area on this page.

For further informations and a bigger overview please visit the Dräger dangerous substances database
Dräger VOICE in the net (

A printform of this guide is available in the download area of this page.
Copyright for the above text: Dräger Safety AG & Co. KGaA


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