Wednesday, April 22, 2015

Runaway stirplates?

Thanks to a note on the listserv of the ACS Division of Chemical Health and Safety, I am made aware of certain models of hotplate/stirrer that seem to turn on by themselves and overheat. Here's a bulletin from the Division of Research Safety at UIUC:
Over the past ten years there have been multiple incidents of hotplates spontaneously heating in the OFF position leading to fires and explosions. Lawrence Berkley National Laboratory, the University of California, University of Pennsylvania, MIT, Oak Ridge National Lab, and Northwestern University have issued safety warnings due to incidents on their campuses related to hotplate malfunction. Hotplates purchased prior to 1984 do not have temperature feedback controls. In particular, the models Corning PC-35 and PC-351 and the Thermolyne Model SP46925 are inherently unsafe by their design. Such older models can spontaneously heat with the heater dial in the OFF position. Other hotplates with reported malfunctions include Corning models PC-200, PC-220 and PC 420 as well as Fisher Isotemp.
This is the first I've heard of it, although I'm not especially surprised. (Here's a poster from Northwestern and a comment from Oak Ridge National Labs.)

Anyone else hear about this? I presume that IKA stirplates don't have this issue, but I dunno.

UPDATE: Nope, Anon1226p in the comments has a picture of an IKA stirplate burnt up because of this issue as well. 


  1. Actually... I had the same kind of problem with an IKA plate: I was stirring a (fortunately aqueous) solution at RT, so the heating was off, and left for a 1-hour seminar. When I came back, I found the plate had melted and the cork ring half burnt (see the picture there:
    It turned out (after autopsy) that the mechanical controls inside were defective; from this day on the safety people ask us to use only plates with the "safety control" mention.

  2. I have also experienced a "runaway" stirring hotplate. The hotplate was older and used for evaporating nitric acid solutions in an operating hood. Its final operation was the slow evaporation of a nitric acid solution on about 18 PTFE beakers, left on a low heat over night (a common and approved procedure in the laboratory). Came in the next morning to find 18 melted/somewhat charred PTFE beakers and a very hot hotplate. I didn't measure the surface temperature. We disassembled the hotplate and found all of the internal controls were corroded beyond recognition. The switch that controlled "low" vs. "high" heat was shorted in such a way to draw maximum power. A couple of lessons learned/reinforced:

    1. Do preventative maintenance on EVERY piece of laboratory equipment, even the most mundane stuff. The incident cost 2 days of a tech's work and hotplate replacement. (Root causes - nature of the operations (corrosive digestions/evaporations) and failure to perform PM, leading to switch failure).

    2. Containment is key for unattended operations.

    3. If you're going to have a fire, the best place to have one is in an operating laboratory chemical hood.

  3. I saw burned out hood from a rheostat controller of an oil bath, it failed in the middle of the night, the silicone caught on fire which incinerated the hood. It was at Scripps FL, in Roush group. Fortunately, a plastic water pipe on the back of the hood bursted and acted as a sprinkler. The lab (and nearby NMR room) got ankle high in soot water, it ruined our spare NMR probe, NMR amplifier and rained into some mass specs a floor below. The two people working in that hood lost a great deal of material, even including notebooks.