The role of powder physicochemical properties on the extinction performance of an extinguishing powder for sodium fires

Abstract

The French Atomic and alternative Energy Commission (CEA) aims to reuse its sodium fire (carbonate base) extinguishing powder after long term storage (stock from the dismantlement of its old sodium facilities). As the composition of the powder appears to change during the storage, the efficiency on the extinction as a function of the physicochemical properties was questioned. Small sodium fire extinction experiments were carried out with powders of different compositions. The results demonstrated a dominant role of water of crystallization on the extinction. Two steps are proposed for the extinction mechanism that includes: (1) the formation of liquid sodium hydroxide and (2) the melting of carbonate mixture at eutectic composition. The sodium hydroxide behaves as a protective layer and insulates the sodium surface from prolonged contact with oxygen. Consequently, it provides rapid decrease of temperature, unlike the slow melting of carbonates eutectic and its porous layer formed due to its higher viscosity. The presence of trona (aging product) does not alter the extinction capacity of the powder. To extrapolate the results to large fires, 35 g of water of crystallization are necessary to extinguish 1 m2 of sodium pool fire. Finally, the particle size appears to be a non-significant parameter to the quality of extinction except for the spreading performance.