Testing the soak time of NBC filters and activated carbon to protect against toxic gases used for military purposes (STS 022)
Only activated carbon may be used in NBC protective filters, as tests have confirmed its protective properties. On safety and cost grounds, the filters must be filled in a laboratory setting. This means that tests on activated carbon for use in large filters (collective protection) are first carried out in appropriately scaled test tubes. However, tests can be carried out directly on small filters for use in individual breathing apparatus.
The laboratory adheres to strict operating conditions (ventilation rates, climatic conditions, and gas concentration) when measuring the soak time of the filter or the protective membrane. The soak time (and permeation time) is the length of time it takes for the filter capacity to become depleted – this leads to a dramatic increase in the gas concentration permeating the filter and to the attainment of the risk threshold (permeated gas concentration).
NBC protective filters are designed to cope successfully with several large-scale chemical attacks.
The testing laboratory also has a modern sorption test facility (SOPRAN), which allows for the safe testing of toxic substances across a wide range of conditions:
| PARAMETERS | VALUE | COMMENTS |
|---|---|---|
| Ventilation rates | 0.5 … 6 m3/h | Continual or intermittent(*) |
| Temperature | 10 … 40 °C | |
| Humidity | <1 … 95 %rF | |
| Gas concentration | 1 … 10 g/m3 | Typical range depending on gas |
| Permeated gas concentration | 1 … 10 mg/m3 | Typical range depending on gas |
| (*)tests on protective mask filters, 10 … 30 pulses per minute | ||
The sorption performance of filters against military-related substances, such as cyanogens chloride, chloropicrin and hydrogen cyanide, is routinely tested. Tests with arsenic, phosgene and dimethyl methanphosphonate can be carried out on request.
As a general rule, the water absorption behaviour of activated carbon filters determines their performance capacity. However, only limited tests of this nature can be conducted during the manufacturing process of activated carbon. Consequently, the pre-conditioning procedure which enables the simulation of real-life working conditions is decisive in these tests. To this end, the laboratory uses a wide range of instruments under well controlled climatic conditions.