Why should you never use water to suppress a grease or electrical fire in a lab?

Why should you never use water to suppress a grease or electrical fire in a lab?

• A. Water can spread oil fires and conduct electricity, increasing burn and shock risk; use an appropriate extinguisher or disconnect power if safe.
• B. Water cools the fire effectively.
• C. Water is always safe on any fire.
• D. Water improves chemical reactions.

Answer: (A)

Water isn’t appropriate for grease or electrical fires because its properties can worsen both situations. In a grease fire, the flame is from oil, which is less dense than water. Pouring water onto burning oil causes the water to sink, push the oil upward and outward, and rapidly vaporize into steam. That rapid expansion can splash burning oil and loft flames, making the fire bigger and more dangerous. For electrical fires, water is a conductor of electricity, so using it can create a shock hazard or energize equipment, increasing the risk of injury and spread. That’s why you should instead use a extinguisher rated for the type of fire—such as a Class B extinguisher for oil fires or a fire blanket to smother—and, if safe to do so, disconnect the power before fighting the fire. If the situation isn’t safe to tackle, evacuate and call for help.

Water isn’t appropriate for grease or electrical fires because its properties can worsen both situations. In a grease fire, the flame is from oil, which is less dense than water. Pouring water onto burning oil causes the water to sink, push the oil upward and outward, and rapidly vaporize into steam. That rapid expansion can splash burning oil and loft flames, making the fire bigger and more dangerous. For electrical fires, water is a conductor of electricity, so using it can create a shock hazard or energize equipment, increasing the risk of injury and spread.

That’s why you should instead use a extinguisher rated for the type of fire—such as a Class B extinguisher for oil fires or a fire blanket to smother—and, if safe to do so, disconnect the power before fighting the fire. If the situation isn’t safe to tackle, evacuate and call for help.