What happened? (Summer 2000) A graduate student was removing some glassware from a hot oven (120 - 150oC) while holding a flask of approximately 200 ml of warm solvent in the other hand (10% ethyl acetate/90% petroleum ether). The flask containing the solvent came within approximately six inches of the oven and caught fire – involving the student's cotton glove and a nearby notebook. Instinctively, the student dropped the flask, breaking it and spreading the burning solvent on the floor. The student quickly snuffed out her glove, grabbed a nearby fire extinguisher (dry chemical) and put out the fire. The student fortunately only suffered 3rd degree burns on her middle finger.
Why did it happen? Ethyl acetate and petroleum ether are flammable liquids. They both have moderate to high vapor pressures (ethyl ether = 73 mmHg @ 20oC, petroleum ether = 2 - 20 mmHg @ 20oC, both would be higher when heated), relatively low flash points (ethyl ether = 26oF. petroleum ether = 20 - 55oF) and flammable limits or ranges in the lower percentages (ethyl ether = 2.2 % LEL -11% UEL, petroleum ether = 1.2 % LEL - 6% UEL). The solvent vapors from the warm solvent mixture traveled to the source of ignition (i.e., the heated oven which is not intrinsically-safe or non-sparking) and flashed back (see "Guide to Reading an MSDS" for an explanation of vapor pressure, flash point and flammable range).
How can a similar occurrence be avoided? Flammable chemicals must only be handled in areas free of ignition sources such as, open flames, static electricity, burning tobacco, hot surfaces (see the Laboratory Chemical Safety Manual, section 1.9).
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