1985 In-Service Training Bulletin - PDF

191S IN-SERVICE TRAINING BULLETIN DANGER BACKDRAFTt A backdraft as defined by IFSTA: rtis an explosion or rapid burning of heated gases resulting from the of oxygen when air is aci:nitted into a building that i...

191S IN-SERVICE TRAINING BULLETIN DANGER BACKDRAFTt A backdraft as defined by IFSTA: rtis an explosion or rapid burning of heated gases resulting from the of oxygen when air is aci:nitted into a building that is :-:eav:.:.l charged by smoke from a fire that has depleted the oxygen content of a building. A backdraft may occur when such a building is opened by the Fire Department without ventilation procedures, or the fire itself effects an The term backdraft probably arose from fluctuating behavior of the smoke a Vlolent rtex;losionrt of gases involved the :..:1 flames. The smoke may ap9ear to change direction :nany ::.mes i:l and out before the explosion. smoke lS pushing out under pressure, care taken :.n 09ening up to let out excessive heat Wlthout oxygen near the base of the fire. " The distinction between an explosion and the rapid burning of heated gases is: "an explosive is a chemical compound or mixture of compounds which suddenly undergoes a very rapid chemical transformation, with the simultaneous production of large quantities of heat and gases. These gases are generally simple substances: carbon monoxide, carbon dioxide, nitrogen, steam, and oxygen. The simul- taneous release of heat causes them to expand so rapidly that they exert an exceedingly.high pressure on the sur- rounding The speed at which this occurs will determine if it is an explosion. 13  7he explosive mixture of compounds can result by the of flammable vapors from involved. ----...._ e : - o.o. -··......, , -"""' _. ---··-··-; ?'"I-- stage. Temperature can be elevated by :.:-: :.::e :..:;:;:er regions of a room. room. ! f this oxygen used during the free burning stage :.s not replenished, the fire returns to the smoldering stage. This lack of oxygen causes incomplete combustion.. , - o - greater of carbon monoxide and smoke. because not enough oxygen is available to sustain However, the heat from the ==ee burning ?hase remains the unburned carbon particles and other flammable compounds are just waiting to burst into rapid, almost instantaneous combustion when more oxygen is supplied. 3ackd.raft that is used to descr1be this phenomenon. For-:u.....,ately, backdraf':s do net occur ·...,i t!"lout fore ·..;ar:"l.:.::g. very nature of backdrafts creates Nhich are discernible. 7he following may indicate a backdra::. or smoke explosion condition: e Smoke under pressure e Black smoke becoming dense gray/yellow Confinement and excessive heat e Little or no visible flame Smoke leaves the building in puffs or at i:-:tervals Smoke-stained windows e Muffled sounds-rattling windows Sudden rapid movement of air inward when open1ng is made 14 by ?roper ventilation. We can ever emphaslze, importance of Wlth the well-;::.anned ::.re a::ac: