Rule 1.
NEVER leave your roaster unattended.
I knew this but ignored it today when I was a few minutes into a 20 minute roast on my Behmor.
I walked inside to answer a Skype and it took me a few minutes to get back to my porch which was completely engulfed in smoke when I did.
I must have inserted the drum wrong because it was not turning and the beans were as charred black as I have ever seen and the chaff was probably close to fire.
Scared some sense into me, and the roaster performed well on a follow up roast that was closely watched.