Practically everyone at the lab uses a microwave oven to heat something – maybe lunch or snack in the common kitchen, or perhaps a liquid or media in a dedicated laboratory microwave. Several times a day even, we place a container in the microwave, press a few buttons and presto – it’s done! What could go wrong with something that simple?
As it turns out, quite a few things have gone wrong at national laboratories, as documented in the Lessons Learned database. For instance at Berkeley Lab last May, agar was heated too long in tightly capped bottles and the force of the rupture of the bottles was enough to blow the microwave oven door off and break the turn plate. Shattered glass was found 20 feet away. Also at Berkeley Lab, the Lessons Learned database shows that in 2013 scorching was observed on a “to go” coffee cup after only 30 seconds of heating, and in 2008 a microwave oven fire occurred.
Another database - the Department of Energy’s Occurrence Reporting and Processing System (ORPS) – lists high-consequence incidents, and several involve microwave ovens. For instance, ORPS shows that in 2000 at Idaho National Laboratory an overcooked potato on a napkin activated the fire alarm and shut down an experiment, in 2002 at Los Alamos burning popcorn tripped the fire alarm, and in 2008 at SLAC reheating un-popped kernels of popcorn led to the evacuation of a large building.
Thankfully no injuries occurred in any of these microwave oven incidents, but shutting down an experiment or evacuating a building can be very costly in terms of time lost. Luckily, these types of incidents can generally be prevented by following a few basic safety guidelines (summarized in this Microwave Oven Safety Tip Sheet, which you can download and laminate).
Preparing to use the oven:
Be sure the oven is clean, since dehydrated debris can catch on fire.
Use the proper container. Glass, tempered glass, ceramic, wax paper, parchment paper, plain paper towels, plastic that is explicitly labeled as microwave safe are safe for heating if used according to instructions. Never use aluminum foil, anything with metallic trim, foam-insulated cups or dishes, single-use plastic containers, or any container that could melt or catch fire.
Loosely cover the container to prevent splatter, making sure that steam can escape.
Use the correct setting and time for the intended use. Note that liquids, especially, can become very hot if heated too long – try 30 seconds.
While the oven is in use:
Stay in the general area so you can respond at the first sign of scorching, smoke, flames, or sparks. Press the stop button or unplug the oven, and if the content has caught fire, keep the oven door closed.
After the oven is off:
Prevent scalding by not overheating liquids and by opening heated containers pointed away from you.
Prevent a container from shattering by never overheating a tightly closed container, and not subjecting a container to rapid temperature changes.
General safety tips:
Only plug the oven directly into the wall socket, never into a power strip.
When plugging into the wall socket, be sure to grasp the plug so that you will not contact the metal prongs.
If the oven operates with the door open, shut the door and turn the oven off immediately, unplug it, mark it for salvage, and do not try to use it again!
Check for appliance recalls to prevent spontaneous fires (unrelated to cooking).
Resources
Microwave Oven Safety Tip Sheet (Laminate and hang near the microwave)
Lessons Learned and Best Practices Database: https://lessonslearned.lbl.gov/general/home.aspx?message=
- UC Berkeley EH&S http://ehs.berkeley.edu/laser-safety/nir-manual-appendix-c-microwave-oven-safety-guidelines
