Editor:
As I watched the thick, black smoke pour from the Houston pellet mill on July 10, I realized what the secret ingredient is that causes these horrendous explosions and fires.
When a pine tree is attacked by mountain pine beetles, it releases a tremendous amount of pitch, commonly referred to as a 'pitch-out', which typically saves the tree from a small number of these invaders.
When it is attacked by a large number of beetles, it's defences do not save it and it dies anyway, leaving the tree full of pitch.
As these trees slowly dry and harden, this pitch hardens too and that is what is mixed with the dust now.
Before this, most of these trees were still too wet, and the pitch stayed in larger, not so burnable particles, but now that the resins have hardened enough to be 'ground up' along with the finer dusts that are produced, it is a nearly perfect flammable substance; wood and something that burns like hot tar.
One only has to look at the blackness of the smoke produced to determine that it's not just wood burning anymore.
Joseph Driscol