I cut four - 2" holes around the bottom of my barrel. Barrel sits up on four bricks - evenly spaced around the barrel. This eliminates the chance of a "hot barrel bottom" starting a grass fire. When the barrel fire goes out - I have a barrel lid for on top. No chance of sparks floating anywhere.
Actually a burn barrel works on the same principle as rocket stoves.
I recall once when as a group we wanted to have a lobster fest.
My solution was 6 cinder blocks and a 5 gal metal pail that was suitably pierced and loaded with dry wood, twigs etc.
Friends were amazed to see how fast that water was boiling.
Otherwise said, I had made a large rocket stove or small burn barrel.
In Lane County Oregon, you can be fined for burning anything a Burn Barrel. Its just straight out illegal in the entire county. Doesn't matter much to me as you can build and burn just about as big an open burn pile as you want.
Mahindra 1538 with backhoe, Massey Ferguson 156 gas
It is fun and somewhat useful to use a leaf blower to speed up the fire. I might have to try making a new burn barrel with fancier vents. Current barrel was vented by shooting it. My daughter enjoyed helping at least. I'd rather build one like my parents had. They built a burn pit out of cinder blocks and had a metal grate to keep burning cardboard etc from blowing out.