What does a saponified film do to help prevent re-ignition?

• A. It increases evaporation.
• B. It makes the oil more flammable.
• C. It reduces oil viscosity.
• D. It acts as a barrier between fuel and heat and reduces evaporation of oil, lowering re-ignition risk.

Answer: (D)

The saponified film forms a soapy blanket on the surface of the oil. This layer acts as a barrier between the fuel and the heat source, while also cooling and reducing the rate at which the oil evaporates. With less vapor reaching ignition temperatures and heat transfer slowed, the chance of the fire reigniting after it’s been knocked down is lowered.

Increasing evaporation would make reignition more likely, so that option isn’t helpful. Making the oil more flammable isn’t what the film does. Changing the oil’s viscosity isn’t the key effect here. The protective, vapor-suppressing barrier is what makes the saponified film effective.