[rcecale]

"FLAMMABLE SOLID.
A solid, other than a blasting agent
or other explosive, whether in elemental or alloy form, that is
capable of causing fire through friction, absorption or mois-
ture, spontaneous chemical change, or heat retained from man-
ufacturing or processing, or which has an ignition temperature
below 212°F (100°C) or which burns so vigorously and persis-
tently when ignited as to create a serious hazard. A chemical
shall be considered a flammable solid if upon testing using the
method prescribed in CPSC regulations, as set forth in 16 CFR
Section 1500.44, it ignites and burns with a self-sustained
flame at a rate greater than 0.1 inch (2.5 mm) per second along
its major axis."

Source...

Kinda like tires, I guess. Not inherently dangerous until you light them on fire...

Randy