Experimental Studies of the Electrical Breakdown of Fire Extinguishing Powders

The method for determining the breakdown voltage in the air suspension of fire extinguishing powder, simplified and more appropriate to the actual conditions of such powders use is proposed and tested. Experimental studies of the electrical breakdown of fire extinguishing powders in an alternating electrical field — homogeneous and non-homogeneous are presented. Double effect of fire extinguishing powders on the breakdown in a homogeneous electrical field in comparison with air is established. The first option: powders to a small extent complicate the breakdown (increase the breakdown voltage), which is due to the high electrical strength of solid dielectrics. The second option: powders slightly facilitate the breakdown. Presumably, this is due to the abnormally high polarizability of one of the components — monoammonium phosphate (ferroelectric). Due to the avalanche-like polarization caused by the ferroelectric, the uniformity of the field is disturbed, which reduces its electrical strength. In an inhomogeneous electric field, the breakdown voltage was about one third lower than in a homogeneous one, and exactly corresponds to the breakdown voltage of the air. In a homogeneous field between the electrodes the «bridges» of powder particles containing monoammonium phosphate appeared and continued to hang even after the breakdown. An unexpected phenomenon was revealed: a relatively weak dependence of the breakdown voltage on the presence of moisture in the extinguishing powder. It is advisable to continue research in this area. The main conclusion: fire extinguishing non-conductive powder does not participate in the electrical breakdown that goes through the air between the powder particles. In view of this, the voltage of 1 kV seems an anachronistic one, at which the use of powder fire extinguishers is allowed, while for carbon dioxide fire extinguishers this figure is 10 times higher (though the electrical strength of carbon dioxide is 0.9 of the air electrical strength). Since the air electrical strength depends on the external conditions (temperature, pressure, humidity, distance between the electrodes), it is proposed to enter relative values for the assessment of the extinguishing powder electrical strength, for example, the ratio of the breakdown voltage to the breakdown voltage in the air.