This European Standard specifies requirements, test methods and performance criteria for line detectors using an optical beam that detect smoke by utilizing the attenuation and/or changes in attenuation of an optical beam, for use in fire detection and fire alarm systems installed in buildings (see EN54‑1:2011 ). This European Standard provides for the assessment and verification of constancy of performance (AVCP) of line detectors using an optical beam to this EN. This European Standard does not cover: line detectors using an optical beam designed to operate with separations between opposed components of less than 1m; line detectors using an optical beam whose optical path length is defined or adjusted by an integral mechanical connection; line detectors using an optical beam with special characteristics, which cannot be assessed by the test methods in this European Standard. NOTE The term “optical?? is used to describe that part of the electromagnetic spectrum produced by the transmitter to which the receiver is responsive; this is not restricted to visible wavelengths.