Comedian and all-around car dude Jay Leno was burned on his face yesterday from a gasoline-related car fire. He is currently recovering at Grossman Burn Center in Los Angeles, according to TMZ. In a statement, he said, “I got some serious burns from a gasoline fire. I am ok. Just need a week or two to get back on my feet.” So, how can something like this happen?

How did Jay Leon’s fire happen?

So the good news, based on the statement to Variety, is that he’ll be OK. But few details have been released, but we know that he was sprayed with gas when one of his steam-powered cars exploded. Because only the left side of his face was burned, his head must have been close to the flashpoint. 

Surprisingly, gasoline in itself does not combust. It is the fumes that are highly flammable. So there were fumes present. But the combo of gasoline and steam is a volatile mix. With steam cars virtually non-existent today, you won’t ever face that type of danger.

But all vintage and classic cars use carburetors, which can lead to bursts of flame or an all-out fire. If a carburetor is operating properly, there should be little to no fumes emanating from it. But if it is leaking, then the float inside the carb is not set properly, allowing fuel to bubble out. If there is a break in the line running from the gas tank to the carburetor, or a leaking carb gasket, then you’ve also likely got fumes present. 

Can an underhood fire happen to you?

Since the carburetor is on top of the engine under the hood, that means the hood is up. That can trap the fumes, but you still need something to ignite it. That also likely came from the carburetor, but not necessarily because of the carburetor.

For something to ignite the fumes, there had to have been a spark or fire. This could come from a plug wire not being secure on the spark plug, or if the carburetor coughed flame from poor timing. In that case, you’ve got a carburetor backfire. 

With the timing off, the combustion that takes place inside each of the cylinders occurs with the exhaust valves either partially or fully closed. That means the only way for the combustion to escape is through the carburetor. So the carburetor backfires. That’s how the flame can erupt from the carburetor. 

So you’ve got flame in proximity to gas fumes. The flame feeds off of the fumes, and you have a fire. And it can be a sustained fire if the engine continues to run, albeit poorly. That’s because fuel is still being pumped, giving a source for the fire to burn until it is shut off. 

We know that Jay Leno’s accident was as much related to steam as gasoline. But for some car enthusiasts, a burped carburetor within a confined area, and an owner possibly adjusting the timing and/or the carburetor, it can be a perfect storm for setting off the gasoline fumes. 

Can this happen in new cars?

It is rarely catastrophic, but it can be. Should the fire burn long enough to set nearly rubber hoses or plastic on fire, then even with the fuel shut off you’ve got an ongoing fire that can easily spread to the wiring insulation, and invariably the interior. Then, the car becomes a funeral pyre. 

Once a carburetor backfires, the engine will stop running, which means there is a short but powerful burst of flame. But it is enough to burn the side of one’s face because it is sudden. There is no time to react. Newer fuel-injected cars can also be a source of flames, but not likely due to the way computers are controlling the works. 

The best news is that Jay will be OK. But in the presence of gas fumes, he and everyone else that likes to tinker with older cars should move cautiously.

Updated 11/15/2022