I’ve used muffle furnaces for two purposes for a couple of decades: Ashing organics out of samples and performing salt fusions for analysis.
Ashing is performed in a low oxygen environment and is done relatively slowly over the course of 12-36 hours. The door must be kept shut during the initial phases of the ashing to prevent deflagration. A rapid introduction of oxygen at temperatures exceeding about 200-250 C can cause a deflagration. Under no circumstances should the door be opened during the ashing process to “check on it.” No, No, No. Put a sign on the door saying “DON’T OPEN THIS.” Most modern furnaces (for at least 25+ years) have the ability to ramp the temperatures up and down. and have overtemp shut offs on them. NB: These furnaces are not “sealed’ and do allow a limited amount of air into them during the process. It’s a “low oxygen” environment, not a “no oxygen” environment. Operation for ashing is usually an unattended operation after working hours; unless the lab director ignores the sign on the furnace door and opens it up. Then it’s attended by the fire department among others.
Salt fusions are a completely attended operation as you have to do sample manipulations during the fusion process.
I am trying to find out how other universities are handling the use of unattended high temperature furnaces that may need to run overnight or even up to several weeks. In particular, I am interested in requirements for when these operations must be monitored continuously, the use of over-temperature shut down devices, and requirements related to flow-through gases.
Thanks for any guidance or policies you may wish to share.
Laboratory Safety Officer
Florida State University
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