Hi Ray.
I've worked with wax for batik and some furniture, and in a nutshell, wax can be a major hazard, but really only has to be melted, no heated past the melt-point.. In a nutshell:
-Keeping the wax temperature close to the melt point rather than hotter means that if wax touches exposed skin, the wax will cause a painful burn, but not a bad burn. Never try to brush wax off of skin or peel it off--your skin can come with it-- instead, keep a bowl of water nearby (but away from the work area) to immediately cool and crack wax if you get splashed.
-Be wary of anything wet near melted wax. A drop of water will flash to steam at temperatures that wax can reach, and can cause the wax to boil over or spatter (like water into hot oil!), and this is a risk with double boilers. Like with grease fires, NEVER NEVER try to put out a wax fire with water.
-HOWEVER, a double boiler is recommended to melt wax because wax can very easily reach a flash-point if direct contact is made with the heat source, cause the wax to bust into flame and/or explode, spattering in all directions. I believe the melting point of beeswax at or near sea level is between 113 F to 151 F (45 to 66 C), below the boiling point of water (212 F or 100 C). Double boilers will not get hotter than the boiling point of water if the pans are not allowed to boil dry. Since the flash point of wax is above the boiling point of water, this gives you a safety margin. I know several people that use crock pots and the like to heat wax, but they keep a thermometer in the wax, stir like mad when its melting, and watch them like a hawk. Once it's melted, they usually unplug the crock pot if they only need it for less than an hour's worth of work. They also tend to never let the wax remain hot for more than an hour or two at a time when using it for longer periods and never leave it unattended, even for a moment.
-Wax is generally hotter when melted than when in the process of melting. Never turn up the temperature to make it melt faster because the wax will heat unevenly, and may be near the flash point nearest the heat source but be cooler at the top. Beeswax begins to discolor at around 185 F (85C), but may not discolor noticeably until it reaches a higher temperature. If the wax is smoking or has changed color, it can be within a degree or two of the flash point.
-The flash point for beeswax can range from 300 to 572 degrees F (149 to 300 C), but is usually at 400 F (204 C); differences are due to purity, types of bees, etc., and beeswax is a mix of over 200 different compounds that vary in their percent composition in any given sample. Boiling points vary widely. The flash point can occur at a lower temperature than the boiling point or vice versa.
-I believe you'd want an extinguisher rated for grease and chemical fires.