NFPA – 17
Dry Chemical Powder, when introduced directly to a fire, causes the flame to go out almost at once. The chemical used is mainly Sodium or Potassium Bicarbonate (BC). Various additives are mixed with the base chemicals to improve the storage, flow and water-repellent characteristics. Dry powders are stable at both low and high temperatures (up to 50 deg. C.) BC powders are non-toxic, but due to the size of the particles (10 to 50 microns), temporary breathing difficulties may occur and personnel must stay clear of the jets to avoid suffocation.
Nitrogen passing through a pressure reduction valve pressurises the tank and nozzles. When a pressure of 0.9-1 MPa bar has been achieved, a pilot valve opens the main discharge valve and the dry powder flows through the distribution manifold to the monitor or hand hose line in operation. The pressure during discharge is kept constant by means of a reduction valve placed upstream of the dry powder unit. The propellant gas system is designed to contain sufficient nitrogen to maintain the pressure during release as well as to clean the pipes and hand hose lines after discharge.
Dry powder system is specially recommended for Chemical plants, filling stations for flammable liquids and gases, tank farms, oil and gas facilities, boiler plants, aircraft hangars, LNG, LPG and chemical tankers, and offshore units.