Burn = Chemicals and not fire. That's the way they mean it around here.
I didn't realize that is what is meant now.
I grew up in a rural area that the local fire departments were volunteer. You could "donate" to them to come out with trucks and babysit burning off your fields in the spring. Yes you had to spray the field down with kerosene, diesel, or whatever to get it to go, but that was a minimal amount from a weed sprayer (generally 2-3 gallons). They were just there to make sure it didn't jump property lines and such or get into the wood line. They appreciated the extra income and a day out. For that matter I once saw some of them popping beers once it got into the center of the field.