Recycling Site fires.

[peteshimmon]

I have heard of a few of these and there was
another big one in Essex yesterday. I have a
question that the chemistry people around here
might help with. I have heard that oily rags
in rubbish can come to ignition. There must
be flash points and need for oxygen but
nonetheless I hear about this fire risk.
So it may be that oil based food contamination
of recycled paper is a risk. Not sabotage
just the way things are. They obviously need
water drenching stuff at such centres.

[ShinAce]

Wouldn't it depend on how volatile the chemical is? If you're dealing with stuff like solvents and finishes used in woodworking, then you should know that the rags used become a hazard as they dry. If we're talking about my fish and chips being a fire risk because the paper soaks up grease, I very much doubt that will cause a fire. Rubbing alcohol is a bigger fire risk than grease at 'normal' temperatures.

[PetersCreek]

Rags soaked in wood finishes such as shellac are indeed a spontaneous fire hazard but only until they dry. Once the volatiles evaporate, they are no more flammable (give or take) than the furniture the finish was used on.

[HenrikOlsen]

But rags with linseed oil (another wood finish) will stay a fire hazard for a while, since the oil doesn't evaporate and it is oxidation or the oil surface while the heat is contained which can cause combustion.

[peteshimmon]

I got round to some googling since I posted
and found the mechanism. As Henrik says, it
is oxidation of something in the oil. If it
is not contained then airflow keeps heat of
the reaction down but contained, heat builds
up to ignition point. I found linseed and
soy mentioned. And soy sounds like food.

So the trash of Chinese glaziers may be
particularly hazardous