First of all, a lot of bees that work in cold climates use the ambient temperature to make air and other condensers much more efficient, so heating the work area can be counterproductive

It depends on several factors, such as the flammability of the solvents you're working with, how big the area is, whether it's insulated and how much ventilation you have

SWIL has seen cars that were painted in freezing conditions heated with catalytic propane heaters to dry the paint, with no fires ever occuring, despite the flammable nature of the paint, and electric heaters using coils as well

Those electric heaters with oil filled radiators should be safer than the above mentioned methods of heating, if their heat output is adequate for the area being heated