“Burning sulfur is very toxic.“
Indeed it is. The oxidation (burning) of sulfur results in SO2, the gas that is that “rotten eggs” smell. Fortunately, if you can smell it, that is when the air concentrations are low, it is not fatal, but when the concentrations go above a couple of hundred parts per million, you can no longer smell it, primarily because you are dead at the point.
Sulfuring cut peaches before drying was my job in the 1960’s.
I’d load the smoke houses, load and light the sulfur then open the doors after a couple days to huge billows of sulfur smoke. Then we’d move them to dry in the sun.
I’m not dead yet
From Western Virginia University:
Without the follow-up of a sulfuring treatment, many fruits – especially apples, pears, and peaches – will gradually darken during drying and storage. Fruits may be dried without sulfuring, but this treatment decreases the loss of vitamins A and C and preserves color and flavor. Sulfuring also deters bugs and souring.