EVS-EN 50241-1:2001/A1:2004

This European Standard specifies general requirements for the construction and testing of apparatus for the detection and measuring of combustible or toxic gases or vapours in ambient air by measuring the spectral absorption by the gases or vapours over extended optical paths, ranging typically from one metre to a few kilometres. Such apparatus measures the integral concentration of the absorbing gas over the optical path in units such as LEL metres for combustible gases and ppm metres for toxic gases.