Flammable materials when exposed to moisture refer to materials that undergo intense chemical reactions and release a large amount of flammable gases and heat when exposed to water or moisture. Some can burn or explode without an open flame.

(1) Intense chemical reactions can occur with water or moisture in moist air, releasing flammable gases and heat. For example:

2K+2H2O=2KOH+H2 ↑+Heat

CaC2+2H2O=Ca (OH) 2+CH ≡ CH ↑+Heat

Even if there was no combustion or explosion at the time, the released flammable gas would accumulate in the container or room and form an explosive mixture with the air, leading to danger.

(2) Reactions with acids are more intense than those with water, which can easily cause combustion and explosion. For example:

NaH+HCl=NaCl+H2 ↑+Heat

(3) Some flammable materials that come into contact with moisture are inherently flammable or placed in flammable liquids (such as metal potassium, sodium, etc., which are immersed in kerosene to isolate the air), and they also pose great risks when exposed to fire or heat sources.