Champ Cars burn methanol fuel. Methanol, unlike gasoline, can be extinguished with water if there is a fire. This provides a nice safety feature.
Nobody knows that they are near a methanol fire until they feel the heat.
This includes the driver, who in a crash may have methanol spilled on his suit. The driver will therefore move flagrantly once he has detected a fire to let other people know that there is a problem. Inside the bag is a sponge-like substance that gives the bag its shape. The idea behind the sponge is to hold the fuel so that, in a severe crash, it does not spray over the driver, other cars or the track. The engine burns methanol at a rate of approximately two miles per gallon, meaning that the car must make a pit stop for fuel approximately every 70 miles or so.