Lesser of two evils?

I had a gas mask in the war - we all did.  I seem to remember that it was an offence to go out without it.  It was, of course, meant to keep us safe in the event of a gas attack.  What we didn't realise back then (thank goodness) was that the gas mask was probably far more dangerous to our health than the gas attack.  The filter in the mask was made, believe it it not, from blue asbestos and arsenic - both highly toxic substances.