Abstract: A scattered radiation fire detector having radiation sources of different wavelengths and a scattered radiation sensor, which are arranged and formed so that their optical axes are directed at a common centre of a scattering volume. A sensor unit is furthermore formed to register forward scattering I1(?1,fwd) of a first radiation source, forward scattering I2(?2,fwd) of a second radiation source and backward scattering I3(?1,bwd) of a further first radiation source, to calculate scattered radiation intensity quotients Q1=I1(?1,fwd)/I2(?2,fwd), Q2=I1(?1,fwd)/I3(?1,bwd) and Q3=I2(?2,fwd)/I3(?1,bwd) and to detect the existence of a fire situation using the scattered radiation intensity quotients.

Abstract: The invention relates in particular to a scattered radiation fire detector (1) having radiation sources (2, 3) of different wavelengths and a scattered radiation sensor (4), which are arranged and formed so that their optical axes (9, 10) are directed at a common centre of a scattering volume (5). A sensor unit is furthermore formed in order to register forward scattering I1(?1,fwd) of a first radiation source (2), forward scattering I2(?2,fwd) of a second radiation source (3) and backward scattering I3(?1,bwd) of a further first radiation source (2), to calculate scattered radiation intensity quotients Q1=I1(?1,fwd)/I2(?2,fwd), Q2=I1(?1,fwd)/I3(?1,bwd) and Q3=I2(?2,fwd)/I3(?1,bwd) and in order to use them for the decision regarding the existence of a fire situation.