Convection Oven Fire in Lab
A fire started in an older convection oven in one of our labs. The fire did not spread to other equipment or materials.
Previously spilled material on the catch tray at the bottom of the oven and subsequently the material placed in the oven for a drying process.
The "convection" oven temperature was set at 80 degrees C, which is well below the 315 degrees C auto-ignition temperature of the material in the oven. The fan and control thermocouple
were operating properly, and the oven was left unattended.
- The material extended across the entire middle section of the oven, leaving no air gap between the heat source (elements are at the bottom of the chamber) and the control thermocouple
which was positioned at the top of the chamber.
- Since this oven is not a true "convection oven" which circulates the atmosphere within, a temperature gradient was created by the material in the oven. The fact that the material was
6" thick insulating foam made it a worst-case scenario.
- The controller was set at 80 degrees C, but the "insulated" control thermocouple did not warm up, so the controller applied maximum power to the elements.
- This oven does not permit the use of multiple control thermocouples.
- This oven does not have an independent over-temperature thermocouple or interlocked over-temperature controller.
- Ensure that the replacement oven is a true convection oven and has multiple control thermocouple capability.
- Ensure that the replacement oven is fitted with an over-temperature thermocouple and independent interlocking over-temperature controller.
- Minimize the accumulation of material spilled in the catch tray at the bottom of the oven. Incorporate inspection of this tray into quarterly lab audits.
- This lab does not have smoke detectors installed. Response time would have been reduced if the smoke was detected sooner.
- The lab is also a high bay area with a ceiling height greater than 25 feet. The other fire detection equipment would not have activated unless the fire had significantly increased.
Consequently, the fire detection equipment will be re-evaluated as well.
- During the response it was noted that the flammable materials storage cabinet was situated next to the convection oven. The cabinet also had incompatible materials stored
inappropriately together. This finding has been corrected.