Which of the following should NOT be used for extinguishing LNG fires?

Water should not be used for extinguishing LNG (Liquefied Natural Gas) fires because it can exacerbate the situation. When water is applied to an LNG fire, it may cause the LNG to vaporize and expand rapidly, leading to an increase in the size of the fire and potentially creating a more hazardous environment. Additionally, LNG is lighter than water and will float on its surface, allowing the fire to continue burning.

In contrast, foam, dry chemical agents, and carbon dioxide are appropriate extinguishing agents for LNG fires. Foam creates a barrier that can help suppress vapors and cool the fire by insulating the fuel. Dry chemical agents can interrupt the chemical reactions of combustion successfully, while carbon dioxide displaces oxygen and can effectively suffocate the fire. Therefore, in the context of LNG fire suppression, water is the least effective and safest option to avoid further hazards.