Document G6087VKO5pDG75k7pDa414Gyv

43--Fire Protection should be stationed to prevent sparks or molten slag from starting fires or to extinguish fires The watchers should remain at the work location foi at least one houi after the welding oi cutting is completed because some fires escape detection at the time of theu in ception Shields should be installed around spot welders to present sparks [torn leaching combustible materials nearby or fiom lnjuung employees Spontaneous ignition Spontaneous ignition lesults from a chemi cal reaction in which there is a slow genera tion of heat from oxidation of organic com pounds that, under certain conditions, is accelerated until the ignition tempeiature of the fuel is reached This condition is reached only where there is sufficient air foi oxidation but not enough ventilation to cairy away the heat as fast as it is geneiated It is a condition usually found only in quan tities of hulk matenal packed loosely enough for a laige amount of suiface to be exposed to oxidation, yet without adequate an circula tion to dissipate heat Exposuie to high temperatuies increases the tendency toward spon taneous ignition The presence of moisture also can advance spontaneous heating unless the material is wet beyond a certain point Matenals like un slaked lime promote spontaneous ignition, paiticularly when wet Such chemicals should be stored in a cool, dry place, away from com bustible matenal It is geneially agieed that at oidmary tem peratures some combustible substances oxidize slowlv and undei certain conditions can reach their ignition point These include vegetable and animal oil and fats, coal, charcoal, and some finely divided metals Rags or waste saturated with linseed oil or paint often cause fires too The best preventives against spontaneous ignition are either total exclusion of air or good ventilation With small quantities of material, the former method is practicable With large quantities of material, such as stoiage piles of bituminous coal, both methods have been used with success Temperatures of 140 F are considered dan gerous in coal piles If temperatures rapidly 1336 Fit. 43-8 --A sheet metal waste tan constructed to prevent opening the cover more than 60 de grees from the horizontal, thus ensuring automatic closing approach or exceed that figure, it is generally advisable to move the pile or rearrange it to allow better circulation of air Cei tain agricultural products are susceptible to spontaneous ignition Sawdust, hav, gram, and other plant pioducts such as jute, hemp, and sisal fillers mav ignite spontaneously, espe cially if exposed to external heat or to alternate wetting and drvmg Here again, the best pieventive is circulation of air, removal of external souices of heat, and stoiage of ma terial hi smaller quantities Fires m iron, nickel, aluminum, magnesium, and other finely divided metals are sometimes attributed to spontaneous ignition believed to result from the oxidation of cutting or lubri cating oils oi possibly from chemical impuri ties