Influence of the breathing mode on the service life of gas filters

Status:

completed 10/1999

Aims:

Gas filters are tested in accordance with European standard EN 141 "Respiratory protective devices - Gas filters and combined filters - Requirements, testing, marking" with a continuous flow rate which corresponds to the mean air requirement of a wearer of the device performing an activity involving moderate exertion. The natural human breathing characteristic however shows peak flow rates which may be several times higher than the mean flow rate. The resulting high flow rate of the gases is presumed to lead to a reduction in the dwelling time of the gases on the activated carbon surface within the filter. The objective was to establish, initiated by the expert commitee personal protective equipment, to what extent the service life of a filter is influenced by this factor.

Activities/Methods:

Type A, B and E gas filters were ventilated dynamically with the gases specified in EN 141 by means of an artificial lung for simulation of brief increases in flows. As with mask ventilation employing valve control, only the inspiratory phase was simulated in sinusoidal and triangular mode. In order to assure comparability to the test with continuous flow, the same mean flow rates were selected in all breathing modes.

Results:

As expected, the peak flow rates arising in the sinusoidal and triangular breathing modes lead to a reduction in the service life of the filters employed when compared with the continuous measurement. The reduction in service life of type A filters was relatively slight at 15 %, but was considerably more pronounced in the case of types B and E, ranging from 55 to 63 % depending upon the type of test gas. The results thus obtained provide support for the estimation of the actual service life of respiratory filters for protection against gases and vapours.

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