The chemical reaction that cures mixed epoxy is *exothermic*, or heat-generating. If left to cure in a contained mass, such as in a mixing pot, it can generate enough heat to melt plastic, burn your skin or ignite surrounding combustible materials. The larger or thicker the epoxy mass, the more heat generated. A 100-gram mass of mixed epoxy can reach 400°F.
To prevent heat buildup, transfer epoxy from the mixing pot to a roller pan or other wide, shallow container. Fill large cavities with epoxy in multiple layers rather than in a single, thick layer. Heat build up and uncontrolled curing are unlikely in typical bonding and coating jobs because spreading the epoxy into thinner layers dissipates heat.
Mixed resin and hardener become hot and frothy as they thermally decompose, generating toxic vapors. These include carbon monoxide, oxides of nitrogen, ammonia, and possibly some aldehydes. Cured epoxy can emit similar vapors if you heat it too much. This can happen when you use a flame to release epoxy-mounted hardware. To reduce this risk, use just enough heat to release the hardware. If you must do so, work in a well-ventilated area.
While leftover mixed epoxy cures, set the container aside where you can monitor it. Use a fan to disperse vapors and direct them away. Air purifying respirators may not be effective against these vapors.
Spontaneous combustion is a danger when hardeners are mixed with sawdust, wood chips, or other cellulosic materials. When hardener is spilled onto or mixed with sawdust, the air and moisture react with the amine to generate heat. If the heat is not dissipated quickly enough, it can ignite the sawdust. Do not use sawdust or other cellulosic materials to absorb a hardener spill. Likewise, do not pour unused hardener into a trashcan with sawdust or other cellulosic materials.
WEST SYSTEM epoxy resin and hardeners are classified non-flammable because their flash points are greater than 200°F and they evaporate slowly. Furnaces, wood stoves, and other heat sources do not pose a serious fire hazard in the presence of epoxy vapors.