Suck = static, blow = safe?

[Nimby]

There are loads of claims on the web that you should never use a vacuum cleaner to suck dust out of your PC "because of static", and that you should use a can of compressed air to blow it out instead.

Now apart from the fact that all the socketed / surface-mounted chips are grounded and probably safe from static anyway, why would sucking cause static but blowing not? Moving air is moving air after all.

Has anyone ever checked with an electroscope (remember that from O-level physics?) if you get static from a vacuum cleaner nozzle but not from a can of compressed air?

[Nimby]

But you're still moving the dust in the computer at high speed even if you blow it with filtered air from a can.

Bring back Mythbusters...

[Nimby]

Mr Pointy said:

I'm not sure why you think the "chips are grounded": they most certainly aren't.

Hmmm. I'm assuming 0v pin(s) on components to motherboard ground plane, ground plane to PSU ground, PSU ground to case and earth (assuming power lead plugged in to wall socket). Isn't that the path of least resistance any static charge would take?
My meter reports continuity between a USB socket's 0v and the mains plug's earth pin - haven't been inside to probe actual ICs.

[Nimby]

Mr Pointy said:

Yes, on your USB example the 0v lines MAY be at mains earth potential but the +5v & data lines aren't - try putting your meter across them. Now put 20kV on the same pins & see if they work afterwards; that's what static does.

You asked why I thought in-circuit IC's were grounded and I explained. Obviously not every pin is connected to earth - is that how you would define it?

[Nimby]

Mr Pointy said:

Well I don't see why you would think that the fact that one pin is grounded going to save a chip from static damage? What about all the other pins?

The same way lightning conductors work; you only need one point grounded to provide the easiest path.