To go with Crane op's pic... A story told to me. Newly built Company facility donated two rolls of polystyrene foam to the Georgia fire school in Marietta GA. (close to Atlanta, GA) Co wanted the fire department to understand the unique fire properties of the stuff.
Fire school was to be relocated so the staff decides to burn the foam in situ instead of transporting to new location. The rolls were anywhere from 1000 to 2000 pounds. Depending on product. Big rolls about 6 foot tall 5 feet wide. It's an intermediate step for the production of foam tableware. (McDonald containers and such) Guess the staff thought ... We're the fire department, we have a pumper truck and charged lines... Let's burn both at the same time...What could go wrong?
So, they light the rolls. Easy to get started. Just a match will do. Okay... let it get fully involved. Uhh Ohh the smoke is getting dense, black, choking, sooty, and voluminous. Turn on the hose... Ahhh... the fire is out. But NO !!! Like a trick birthday candle, as soon as the hose is turned off, the rolls start to burn again. The plastic foam burns so hot, the plastic melts and flows down. What happens when cold water hits melting plastic ? The plastic immediately hardens. Forming an armored shield against any further water. Meanwhile, the built-up heat is held by the insulating value of the foam.
The smoke was so thick, nearby Dobbins Air Force base runway was closed for 20 minutes.
With planes diverted or circling
I can vouch for the fire & mechanical properties of the stuff from personal career experience.