The biggest risks with a dying microwave aren’t you being blasted by microwaves (although this can happen). It’s fire because the magnetron coils heated up and melted their insulation and shorted out.
If a fire occurs INSIDE the microwave DO NOT OPEN THE MICROWAVE! Leave it closed and unplug it or pop your circuit breaker.
Smaller fires will typically burn out inside a microwave due to lack of fresh air.
Once it’s unplugged, you can use a Class ABC (or Class K) fire extinguisher and then open the door and blast it IF it seems like the fire might not be dying down or is growing. This can be pretty dangerous as a giant plume of fire and smoke will shoot out if you open the door and can cause the fire to spread rapidly so use your best judgement.
For fires in an oven, just leave the door closed. It will burn out due to lack of oxygen. Have a fire extinguisher on the ready though.
When in doubt, leave the area and call for your fire department.
In terms of microwave leakage, this is highly unlikely unless there are obvious holes in the microwave. Modern microwaves have pretty substantial shielding and safety mechanism to prevent microwave leakage.
You’d also know pretty quick if you’re being hit with microwaves. The areas where it hits you would heat up and be pretty uncomfortable.
Another telltale sign of excess microwave leakage is it kicks everyone off 2.4 GHz wifi because it over-powers the signal. This was actually a pretty frustrating problem back in the day when wifi was new and wasn’t able to handle interference as well, lol. You’d know someone was microwaving something because your signal would drop substantially.
The second risk is electrocution. Microwave transformers are no joke and you should never ever take a microwave apart unless you know exactly what you’re doing.
If you’re getting a new microwave, look for one with “inverter technology” as these allow for actual variable power output instead of just altering the duty cycle. In other words, with the “inverter technology” the microwave uses less energy to emit lower energy microwaves. This will ensure your food is always being hit with microwaves and actually heats better and more evenly.
This is contrary to your run-of-the mill boring microwave which uses “duty cycles” which is a fancy way of saying “how long is the thing on emitting full power vs. how long is it not” which will heat up food unevenly.
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