Fire from Sparking Hot Plate
Monday, September 26, 2016
One researcher from a lab was attempting to gently heat a flask containing ≈ 150 mL of diethyl ether in our lab for recrystallization. The hot plate was set to 2, a relatively low heating setting for this hot plate as determined by the researcher from using it before. The hot plate had just been started. This hot plate was more than 35 years old, and had been recently repaired.
As soon as the flask containing the ether was placed on it, a small amount of ether boiled out or bumped out, or it may have come out because of the inadvertently placing the flask on the plate with more force than intended. The researcher checked that the hot plate wasn't very hot when he placed the flask on it.
But the ether that came out caught fire immediately. Even though such an amount of ether would typically just boil off the hot plate, but it seems the fire started near the back part of the plate, probably because of a spark from the hot plate. The fire was mostly in the Erlenmeyer flask. The researcher removed the flask from the hot plate, and put it on the hood floor, but it had burnt out most of the ether by that time. Another researcher saw the fire from the window of his office and came in quickly. By this time the fire had mostly burnt out, although he quickly took a type C fire extinguisher to put out the remaining fire. Nobody was injured and the hood was not damaged, thanks to the timely action.
The flask however broke when it fell from the lab jack mounted hot plate. The hot plate was checked right afterwards, and it was only slightly warm. After discussion, we think the fire may have been caused by the sparks from the old heating plate, even though it had been repaired recently. Likely the sparks ignited the ether vapor to cause the fire. The hot plate was checked for its temperature right after the incident, and it was just lukewarm.
Flasks should only be filled up to 1/3 full to prevent overflow and spills during heating or small bumps during handling.
Chemistry Safety Committee- strongly advises against using ether for re-crystalization. Ether was historically commonly used because of its solubility. However, anytime you are heating close to or above a solvent’s flash point is inherently hazardous. Ether has an extremely low flash point which is easy to heat above. A safer choice would be a solvent with a higher flash point or select a different purification method.
In case of low boiling solvents such as ether, heat a water bath separately. Then remove the heat source like hot plate, and use water heat to boil or heat up. This would be enough to boil off the volatile ether or dichloromethane or any other low boiling solvents.
Make sure that hot plates work well before using. Do not use equipment if you’re not sure how well it works. Do not turn the hot plates on BEFORE heating the solvent.
In case of fire, determine if you can do something about it,
First reaction should be to shut the sash or cover the flask with a beaker. Never try to handle flammable liquids with an active fire. These are easy to spill and spread the fire.
Otherwise, just use the fire extinguisher. Get the fire extinguisher replaced after its pin has been pulled.
If you can't do something call 911, and evacuate the lab.
Go to http://z.umn.edu/safetyfactsheets for factsheets about hot plates and fire extinguishers.