News and Announcements

Warning about malfunctioning hotplates

 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.

Newer models with TRIAC or microprocessor-controlled heater switches may spontaneously heat when liquid comes into contact with the electronics.

A related problem is the malfunctioning of external temperature probes that cause the hotplate to heat excessively.

DRS recommends the following to prevent accidents caused by hotplate overheating:

• Discard hotplates purchased prior to 1984 and hotplates in disrepair.
• Periodically test the function of the off switch to verify that it works and the heating device quickly cools. If the device fails the test, take it out of service immediately.
• Unplug hotplates when not in use.
• If only stirring is required, use a stirrer only, not a hotplate/stirrer combination.
• When acquiring new hotplates, select a housing design that is hermetically sealed to protect electronics from liquids and gases. In addition look for two independent temperature control circuits that shut off power when the temperature exceeds a selected limit.
• If an external probe begins to show occasional malfunctioning such as temperature deviation or fluctuations, take it out of service immediately as it will fail sooner or later.

References

1. Safety Issues of Hotplate Heating Controls, poster from Northwestern University
2. Deflagration and Fire from Malfunctioning Lab Stirrer/Hot plate , Oak Ridge National Laboratory, June, 2014
3. Hotplate Advisory! , MIT, 2010
4. Hot Plate Switch Failure, Lawrence Berkeley National Laboratory Lessons Learned, 2005
5. Hot Plate and Heating Device Safety Advisory, University of California, 2011