Occupational Health and Safety Hazard Alert - Overheating of Ovens and Other Heating Devices

Occupational Health and Safety has received several reports of failures in temperature controllers associated with laboratory ovens, incubators and furnaces in recent times. In each case, instead of shutting off the power supply, the unit's failure resulted in full power being applied and very high internal temperatures were reached. This has resulted in the contents of the ovens, etc., being burnt and destroyed. There is obviously a potential for starting a fire in the room housing the equipment.

The known failures have occurred for a variety of controller types ie. solid state, digital and analogue. Given that a temperature controller of any type is associated with an electrical heating function for which there is a closed circuit, a "failure" in any part of the system may not necessarily result in a "safe" outcome.

In the past, Occupational Health and Safety has been involved in the investigation of fires at the University which have resulted from malfunction of a variety of electrical appliances and equipment (such as refrigerators, projectors, motors, stirrers, heaters) which have been left switched on and unattended. Australian Standard AS 2243.7 - 1991 Safety in Laboratories Part 7: Electrical Aspects has a section on "Live Unattended Equipment", paragraph 5.2(c) is specifically relevant to common equipment such as ovens, heaters, driers, autoclaves, incubators and furnaces. To avoid "overheating" occurrences in thermostatically controlled equipment, the following control measures should be implemented:

1. Identify all electrical equipment which may be left switched on unattended.
2. Fit a manually resetting over-temperature cut-off switch which can be set to operate at a temperature slightly higher than the upper limit of the controlled temperature, if one is not already part of the equipment.
3. Comply with all the other requirements of section 5.2 of Australian Standard AS 2243.7.
4. Controller units and over temperature cut-out switches are to be maintained and tested regularly, according to the manufacturers recommendations.
5. Ensure that any new equipment proposed for use of the University has both temperature control and manually re-setable oven temperature cut-off switch prior to purchase.

Please contact Occupational Health and Safety enquiries on 51016 or email if you have any queries in relation to this matter.

11 March 1997