Propane Trap

The Gasoline Trap is one of the three main traps used in the Half-Life 2 chapter "We Don't Go To Ravenholm..." and the Half-Life 2: Episode Two chapter Freeman Pontifex by Gordon Freeman against the many zombie hordes he faces in both situations. It consists of a large tank of gasoline that has a hose leading out of a valve on its side. When the valve is turned, the gas begins to flow out of the hose and fill the immediate vicinity. If a bullet is fired into the exiting stream of gasoline, the area around the tank and anything around it is engulfed in flames. The fire will continue to burn until the valve is turned again and the gas is cut off.

They are extremely effecting against zombies and headcrabs due to the fact that the fire not only does damage to them, but also because it slows down their movement dramatically and allows them to catch other creatures on fire. While they are on fire however, they can do significant damage to Gordon simply by running into him and burning him.