The use of hand warmer exhaust hole

Mainly explosion-proof, reduce the threat . Hand warmer is the use of physical and chemical principles of the development of automatic heating health supplies, literally warming the hands, generally filled with water, there is a heating device, the electricity will be energized, you can heat the water inside, to achieve the purpose of heating. But if you use it for a long time, it will be filled with air, heating will become larger, there is some danger over time, so it should be regularly deflated.