Risk assess the heater/s and revise your fire risk assessment to include the heaters. I have experience of LPG heaters causing fires and damage to personal property when not sited correctly. Store the gas properly and don't have cylinders free standing.

Risk assess the heater/s and revise your fire risk assessment to include the heaters that's what I thought would be required

Apart from high moisture content, various combustion products of the heater and other combustion products if the unit has anything in the atmosphere from whatever process is running within ? Is it gas ? Or is it kerosene/diesel (if so, get me outa there) You can also get heaters where the air is blown over electrically heated ceramic exchangers...much more sociable. I expect we're talking rock-bottom cheap here though....so probably they will be red diesel....high sulphur content.

Kerosene. I'd still be out of there. I flatly refuse to work in any area where heating is by anything that exhausts into the workplace atmosphere. That includes propane/butane. You would have to ensure that there is an adequate supply of air, and that should not mean an open window but more an open door. The only ones I consider even slightly useful are those where the burner waste gases are vented externally to the heated building....via a chimney/flue. Exhaust gases include carbon monoxide/dioxide, carbon (soot) as well as water vapour.

Putting the bottles near[er] to the heat source increases the output from the bottle. Seriously. LOADS of people use a bottle too small for the heater. Seriously. If the bottle is too small the gas drawn from the bottle will exceed the withdrawal rate FOR that bottle, leading to excessive frosting and reduced gas flow (because the liquid gas cannot vaporise fast enough to match the needed amount) Seriously. At one time, with the temperature in the minus figures, and with a large heater, the amount of gas needed for that heater at that temperature meant that two large propane cylinders were used per heater. I went home. Even with the heater[s] the temperature was too cold....due to the need for an ample air supply the doors could not be closed.