  Standard laser based fire detection systems are often based on measuring
variation of optical signal amplitude. However, mechanical noise interference
and loss from dust and steam can obscure the detection signal, resulting in
faulty results or inability to detect a potential fire. The presented fire
detection technology will allow the detection of fire in harsh and dusty areas,
which are prone to fires, where current systems show limited performance or are
unable to operate. It is not the amount of light nor its wavelength that is
used for detecting fire, but how the refractive index randomly fluctuates due
to the heat convection from the fire. In practical terms this means that light
obstruction from ambient dust particles will not be a problem as long as a
small fraction of the light is detected and that fires without visible flames
can still be detected. The standalone laser system consists of a Linux-based
Red Pitaya system, a cheap 650 nm laser diode, and a PIN photo-detector. Laser
light propagates through the monitored area and reflects off a retroreflector
generating a speckle pattern. Every 3 seconds time traces and frequency noise
spectra are measured and 8 descriptors are deduced to identify a potential
fire. Both laboratory and factory acceptance tests have been performed with
success.
