Uses for left-over styrofoam packing material

I was going through the garage today and found some styrofoam I had saved because it was fairly dense and rectangular... I thought I might use it sometime. Well, I had saved it for a decade and never used it, so instead of ditching it, I decided to open up the attic and toss it in there. There's nothing in the attic except attic dust and hot air anyway. I was hoping it would act as an insulator.

Is it safe to put foam products in the attic, or should only approved insulation materials be used? Should I be worried about spontaneous combustion?

Foam gets wickedly ugly when on fire. I believe home insulation must meet some kind of fire regulations. I found this nifty link:

http://www.naima.org/pages/resources/library/html/BI472.HTML

It looks like some useful info!

I'e used it to line speaker boxes and a bunch of other things. I hate throwing it out. We used to be able to recycle it up here but cutback's have killed it.

Interesting link... I wonder if filling the attic with scrap fiberglass insulation would make a difference, or should I just leave it empty? Maybe I should invest in an attic fan.