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3.1. Limits of protection
The duration of the filters depends on the class and the use: humidity and temperature of inspired air, work rate,
concentrations and combinations of the toxic in the environment. For these reasons it is impossible to predict the duration
of use if the above information are not known. To evaluate the dangerousness of toxic, gas or particle, the Threshold
Limit Value (TLV) is used. TLV represents the maximum concentration of a substance that a man can be exposed to, for
a shift of 8 hours, without consequences or damage.
3.2. Gas filters
Gas filter of higher class can be used (with the same mask) in environments where a lower class filter is required, in the
below table are listed the toxic concentration (expressed as Multiple of the limit value TLV) that shouldn't be exceeded for
each type of mask.
Type of Mask
Multiple of the limit value
TLV
Observations - limitations
Half mask or quarter mask 30
It must not be used in case of gas concentration higher than
those fixed for class 1, 2 or 3 gas filters (see related table)
Full face mask or mouthpiece
devices
400
Filter class Filter Capacity Maximum allowed gas concentration *
1 Low 1000 ml/m
3
= (0,1 vol.% = 1000 ppm)
2 Medium 5000 ml/m
3
= (0,5 vol.% = 5000 ppm)
3 High 10000 ml/m
3
= (1,0 vol.% = 10000 ppm)
* The old denomination of the gas concentration is shown in brackets.
According to the present production standards, as a rule the following classes of filters correspond to:
Class 1 Gas filter small filter equipped with special screw-in or with snap-on connector
Class 2 Gas filter normal filter or filter equipped with screw-in connector complying with EN 148/1
Class 3 Gas filter filter to be connected to the mask by means of a corrugated hose
Filters for NO must be used only once. CO filters must be used only once for the maximum time specified by the filter
class (20, 60 or 180 minutes) and anyway they must kept in sealed package until use.
3.3. Protection capacity and test conditions of type A, B, E and K gas filter according
to EN 14387:04/A1:2008 standard
Type and
class
Test gas
Concentration of test gas
(PPM)
Minimum breakthrough time in test
conditions (min)
A1 Cyclohexane (C
6
H
12
) 1000 70
B1
Chlorine(Cl
2
)
Hydrogen sulphide(H
2
S)
Hydrogen cyanide(HCN)
1000
1000
1000 20
40
25
E1 Sulphur dioxide(SO
2
) 1000 20
K1 Ammonia(NH
3
) 1000 50
A2 Cyclohexane (C
6
H
12
) 5000 35
B2
Chlorine(Cl
2
)
Hydrogen sulphide(H
2
S)
Hydrogen cyanide(HCN)
5000
5000
5000 20
40
25
E2 Sulphur dioxide(SO
2
) 5000 20
K2 Ammonia(NH
3
) 5000 40
A3 Cyclohexane (C
6
H
12
) 10000 65
B3
Chlorine(Cl
2
)
Hydrogen sulphide(H
2
S)
Hydrogen cyanide(HCN)
10000
10000
10000 30
60
35
E3 Sulphur dioxide(SO
2
) 10000 30
K3 Ammonia(NH
3
) 10000 60
It must be noted that the breakthrough time of the filters in actual use conditions could be longer than in laboratory test
conditions.
3.3.1. Multi-type filters
Multi-type filters offer protection against various gases. The conditions and limits of use of these filters are the same as
those for gases.