On Tue, 13 Jun 2017 16:16:01 -0500, Jon Elson wrote:

so we have enough humidity that ESD is a fairly rare phenomenon. I have
used vacuum cleaners to clean old computer gear, and never had damage,
although I was concerned about the possibility.

I'd be more worried about the action of brushing itself giving rise to
static charges. It's hard to know for sure what

I have seen a fat spark produced when firing off a CO2 fire
extinguisher, which seemed like a pretty big design defect.

Yes, been there; done that. In fact a gave a co-worker a pretty nasty
shock by using a CO2 extinguisher which must have charged me up to 10s of
thousands of volts whilst I put out a fire with it. It was a very noisy
situation so I needed to shout into his ear to make myself heard and this
terrific blue spark shot straight from my nose to his ear! Had no effect
on me but sent him reeling. You should have seen the look on his face! :-