>> can it catch fire????
Yes. Haven't heard about 'compost fires', BUT there has been many a barn that has burned down due to wet hay in the hayloft.
Same principle. Might not be the heat ... could be the methane from biologics that gets 'sparked' in a barn. Don't know for sure. If methane, accumulation to danger level in outside compost might be problematic.
Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...