SR 90 Airline is a compressed air half mask with filter back-up, designed for connection to an appropriate compressed air supply with breathable air. The overpressure which builds up in the mask prevents contaminated ambient air from reaching the user. SR 90 Airline can be used as an alternative to filter protection in all situations where such protection is recommended. This applies particularly to heavy work or long-duration work, and where contaminants do not provide adequate warning, or are especially toxic. The mask is made from a material that does not cause sparks in the event of friction, which allows it to be used in explosive or inflammable environments. The control valve is fitted with a warning whistle which operates if the air quantity falls below the recommended value. A flow meter for monitoring air flow is included. Compressed air should be purified with a Sundströms SR 99 compressed air filter.