Years ago, I had the unfortunate experience of extinguishing a burning man inside a demolition derby car. I broke down in an earlier heat race and was relegated to track flagging duty for the main event.
The incident was caused by a burst transmission line. In those days it was common, especially for those running Chrysler cars, to run external lines to an oil cooler encased in an ice chest behind the driver's seat. The line burst in the area of the floorboard, soaking the driver and was ultimately ignited by the exhaust manifold. In the ensuing panic, he was unable to unlatch his harness. And he could not reach his fire extinguisher when buckled in. I ran up to the car, pointed my fire extinguisher in his lap and pulled the trigger.
It was a pretty traumatic experience to say the least. He spent about 9 months in a burn center. I wish I would've shouted for him to hold his breath, because of the damage from inhaling the fire extinguisher chemicals, his voice is now an octave or two higher than it should be.
No matter what you do, know your equipment and practice for emergencies.