Plastic fires are nasty. Aside from toxic fumes, plastic melts, So gravity will help it spread, if there's a way for it to do so. You're not going to cause a

Plastic fires are nasty. Aside from toxic fumes, plastic melts, So gravity will help it spread, if there's a way for it to do so. You're not going to cause a runaway with a lighter and a pop bottle without working at it. But, say, an electrical short in a closet with hanging synthetics can take off pretty quickly.