1. Alkali Metal Fires
Fires involving alkali metals (such as potassium, sodium, and zinc powder): When water comes into contact with alkali metals, a violent chemical reaction occurs, producing large amounts of hydrogen gas and releasing substantial heat, which can easily lead to an explosion. For such fires, it is essential to select the appropriate extinguishing agent and make rational use of local resources.
2. Fires involving metal carbides and hydrides
For example, carbides (such as calcium carbide) decompose upon contact with water, releasing substantial heat, which can easily lead to the escalation of a fire or even an explosion.
3. Fires involving sulfuric acid, nitric acid, and hydrochloric acid
Such fires should not be extinguished with a powerful water jet, because when acid comes into contact with water, it can splash and flow out, causing injury; moreover, if the spilled acid contacts combustible materials, it may ignite. However, if necessary, a spray water jet may be used for extinguishment. Fires involving flammable liquids that are lighter than water or insoluble in water: in principle, these fires should not be extinguished with water; nevertheless, crude oil and heavy oil can be tackled using a spray water jet.
4. Fires involving molten iron and molten steel
Contact between a scorching-hot object and water poses an explosion hazard. When water is exposed to temperatures of over 1,000°C, it rapidly vaporizes, causing its volume to expand suddenly by more than 5,000 times and triggering a physical explosion. Moreover, at temperatures above 1,000°C, water vapor can decompose into hydrogen and oxygen, leading to a chemical explosion.
5. Fires in High-Voltage Electrical Equipment
In the absence of proper grounding or when the power supply has not been disconnected, water should generally not be used for firefighting. First, water is conductive and can easily cause short circuits and damage to electrical equipment; second, high-voltage current may travel along the water stream to firefighting equipment, potentially electrocuting firefighters and resulting in injury or death.
