A new fire alarm system for electrical installations

Fires in electrical installations are considered to develop in four phases - initiation, smouldering, flame formation and heat development. Cables are among the more sensitive components, with working temperatures around 50 degrees C and fire detection at 70 degrees C. Conventional alarms include smoke detectors. The new technique described uses microcapsules containing powder forming a gas of the Freon type after diffusion. A typical microcapsule loses 4% per year and has a natural life of 10 years. Fabrication methods are described. Detection is by gas concentration, with a sensitivity of 1 to 10 ppm, or by acoustic methods with microphones to pick up the sound of fractures. Pressure/temperature characteristics of various types of Freon mixtures commercially available are given in graphical form.