Re: Microwave "Criticality" Thread --Actual Meltdown Anecdote

[RADPROJECT@aol.com]

Radsafers:
I've followed some of the interest in the Microwave "Criticality" thread 
which has caught the interest of numerous readers. I myself had an experience 
with a microwave meltdown that demonstrates just how high a temperature can 
be reached in a microwave.  Superheated water is one thing.  How about a 
white hot mass of carbon melting borosilicate glass.

The situation as it developed is described below. In the early 1980s before I 
purchased my first microwave, my wife and I stopped to check in on her 
sister's ski house in VT for some reason on our return from a trip. While my 
wife was on the phone with her sister, I decided to make microwave popcorn 
from scratch. I had used a hot air popper for many years and assumed I could 
throw some hot air popping corn into a microwave for a few minutes and do the 
same thing.

I found some popping corn and put it into a white pyrex bowl with a clear 
pyrex [borosilicate] glass top. I had never made microwave popcorn before so 
I set some short time interval to start, but  no popcorn popped. I then 
quickly keyed in some longer time and left the microwave while I went to the 
phone perhaps 20 feet away, to discuss chat  with my brother-in-law. I forgot 
about the microwave since I never heard any popcorn pop. The popcorn must 
have been old and dried out enough that it was just not going to pop.

Apparently, I must have punched in an extra digit on the duration of heating, 
because after some five or so minutes I went back to the microwave and found 
it still running. I looked through the panel and saw an odd "glow" coming 
from within the bowl and the cover could be seen to be sagging [melting] into 
the bowl.

I stopped the microwave and in opening the door saw that there was a mass of 
material in the bottom of the bowl which was glowing white hot. The clear 
pyrex glass cover had begun to soften and had almost melted at its center 
into the bottom of the bowl. The covered pyrex bowl with its white hot carbon 
mass within was very carefully taken out of the micro and placed onto a 
trivet to cool to avoid any further damage to the micro.

Afterwards, in thinking about what had happened, I understood why the Steath 
bomber wings are covered with a carbon containing coating to absorb 
microwaves and prevent or minimize radar signals from bouncing back to radar 
stations trying to track it.

Maybe someone can post the melting point of borosilicate glass, and what 
temperature is approximately achieved in a "white" hot object. This curious 
and interesting happening shows that even a home  microwave oven is capable 
of pumping a surprising amount of energy into an object like a carbon mass, 
and in reaching very high temperatures [if one makes a few mistakes as to 
on-time and inattention to what is going on]. 

I went on to buy a microwave and use it rather uneventfully with one minor 
[ie: it didn't blow off the door, but did make quite a noise] explosion. This 
was a time when an eggplant exploded and filled the micro with eggplant mush 
due to my having failed to poke some steam vent holes before microwaving the 
eggplant to soften the contents for some recipe I was following. 

Thankfully, there has been no morbidity or mortality associated with these 
infrequent microwave "unusual events" leading to any CDC reports or federal 
regulations.

Stewart Farber
Public Health Sciences
email: radproject@aol.com
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