The detector has been designed to signal the presence of a concentration of gas of between 10% of L.E.L. (Lower Explosive Limit) in the environment in which it is installed. This threshold may vary during use with variation of environmental conditions but it will not exceed 20% of L.E.L. during the first 4 years of use.
EN50291 defines the CO level, at which the device must and must not go into alarm. The higher the CO concentration, the quicker the device will give an alarm. This is based on the fact that the poisoning impact of CO is determined by CO concentration and exposure time. The alarm points ensure that the user is always warned when critical situations occur.