In general, heat detectors are suitable for installation in a harsh environment such as the underside of a railroad car or an
engine compartment. Smoke detectors are faster to response but cannot be applied within harsh environments. They are
suited for passenger areas such as sleeping cars of trains, or conditioned spaces. If rapid reaction is needed in a harsh
environment, optical flame detectors could be employed. Ultraviolet detectors are especially sensitive to electrical arcs and
cannot be utilized around electrical equipment. Infrared sensors will react to hot surfaces and often use a “flicker” sensor to
react to the flickering frequencies of flames (5-30Hz). [5]