I was burning weeds very thoroughly one dry day, and came out hours later to find some roots had smoldered their way about 6ft underground and burned the bottom of a cedar fence. This was in bark mulch. I decided after thanksgiving I needed to water after burning.
Think I would move the propane tank as far as possible from the open flame just for safety reasons. You get one chance to get it right. Probably not worth an explosion to get rid of those pesky weeds.
It’s no joke, I used one close to a wooden fence, thought it was fine, left then came back to an inferno, thank god my neighbor banged on my door and I had plenty of fire extinguishers.