Don't Get Caught With a Smoking Heat Gun

The hot air coming from a heat gun may be invisible, but you should treat one with the same respect as a blow torch. And be careful where you set it down. For example, a recently used heat gun was set down in close proximity to a wash bottle containing methyl-tert-butyl-ether, which ended up igniting. There’s also a report of a laboratory worker who was attempting to heat heptane in a Pyrex beaker by hand. When he accidently splashed a bit, the flammable liquid came in contact with the heat gun element, leading to burns on his hand and a destroyed computer.

Here are some safety considerations you should keep in mind when using a heat gun.

Laboratory heat guns are constructed with a motor-driven fan that blows air over an electrically heated filament. They are frequently used to dry glassware or to heat the upper parts of a distillation apparatus during distillation of high-boiling materials.
The heating element in a heat gun typically becomes red-hot during use and the on-off switches and fan motors are not usually spark-free. For these reasons, heat guns almost always pose a serious spark hazard.
Heat guns are a danger in disguise: they pose as serious an ignition hazard as a naked flame. Contrary to the open flame, that admonishes the operator to be carful, a heat gun creates a false impression of safety. Ther danger zone is invisible, but very active. The combination of sparks and forced ventilation over a glowing filament may lead to fire and/or explosion.
The air emerging from a heat gun is very hot indeed and is invisible and so the front end should be treated with all the respect due to a blow torch.
Never use a heat gun near flammable materials including open containers of flammable liquids, flammable vapors or hoods used to control flammable vapors. Take into consideration that the atmosphere in the lab may contain enough flammable vapors to create serious problems.