Back then (290mya) atmospheric oxygen was at a whopping 35% and there is fossil evidence suggesting that all plants back then, even the ones in the coal swamps, were adapted to regular fires that had to be explosive. Conifers evolved during this period, which is why they are so fire-resistant.
A common hypothesis on why the oxygen level got so high during the Carboniferous is because fungi had not evolved enzymes for digesting the lignin in wood. Despite the stereotypical images of coal swamps this was a very cool, dry "ice-house" world similar to our own. The great coal deposits were coastal tropical lowlands that were flooded when an interglacial raised sea levels.