If someone "responsible" in the lab feels comfortable with it, I say go for it!
The students need, at the minimum:
* A way (lots of power resistors in parallel) to make sure the cap is totally discharged;
* Rubber gloves (nasty acids in those things);
* Safety goggles;
* Lab coats (or old clothes they don't mind getting stained);
* Keep their mouths shut (or wear dust masks) until the thing is totally disassembled;
Further safety measures:
* I'd also, if possible, do things in a fume hood or glovebox, though that may be overkill for this;
* Keep some base handy (and do work away from spark sources) to neutralize acids. Remember that acid/base reactions generate H2, and this can cause explosion hazards (though it's not likely).
There are good lessons to be learnt here in electrical safety:
* Make sure things are no longer energized;
* Make sure caps are discharged (monitoring the voltage across the dissipating resistors is a good lesson in and of itself);
* Teaching the students to initially touch things only with one hand, if possible (check for heat on components first, using the backs of one's fingers, which helps to mitigate burn damage, and also minimizes the chance of muscles clamping down on energized things, just in case something was missed) -- you don't want to discharge through the heart, if at all possible.
I've taken many caps apart. In order of what scares me, it's: 1) possibility of squirting acid in my eyes; 2) possibility of getting nasties in my mouth; 3) possibility of getting shocked; 4) possibility of breathing something; 5) possibility of getting burnt from hot components (remote laser thermometers are handy here, too); 6) possibility of staining/burning clothing; 7) possibility of pinching myself with pliers, or poking myself with cap leads (sharp!).
The probability of any of the students getting hurt is minimal, even without a lot of these safeguard steps. But it's a _very_ good chance of teaching them proper safety measures.
/************************************
Down with categorical imperative!
flutzpah@yahoo.com
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________________________________
From: David Strasburger-fac <David_Strasburger-fac@nobles.edu>
To: phys-l@carnot.physics.buffalo.edu
Sent: Wednesday, April 1, 2009 11:53:09 AM
Subject: [Phys-l] dielectric safety
Students in a colleague's lab were pulling apart a defunct portable CD
player today to get parts for another project. One student wanted to know
if it was OK for him to cut open one of the capacitors to see what it
looked like inside. The teacher said she wasn't sure and asked me if I
knew if any of the materials inside were likely to be hazardous. I said I
didn't know.
I feel pretty confident about the safety measures we're taking to prevent
electric shock, but could anyone on the list comment about the safety of
cutting open a discharged capacitor salvaged from consumer electrincs?
thanks
david strasburger
Noble & Greenough School
Dedham MA