Thankfully this is as rare as it is fearsome
In about March 2011, a pilot with 50 flights under his belt was foot launching. After a good inflation and run he stumbled, hitting the ground hard enough that his propeller flexed into the fuel tank, slicing through and causing a mist of fuel which burst into a fireball.
A nearby instructor ran to him, pulling him out before the flames completely engulfed him and his machine. He is recovering with 2nd and 3rd degree burns to his back and arms. It could have been much worse—imagine if he was alone. Still, he will never look the same.
We’ve seen it numerous times where prop tips dug into the fuel tank, causing an explosive misty cloud of fuel vapor as the prop disintegrates. It had never ignited until now. This was a carbon fiber prop which may be more likely to cause a spark when struck against metal. It could have been other sources, too, such as something from the engine exhaust. Maybe the electric starter got activated accidentally during the fall. It’s hard to say.
But what we can say is what needs to be done in the future to prevent it. I’ve seen plenty of paramotors where the prop tips come within 6 inches of the gas tank. Generally 4 inches on shorter props is probably sufficient but, anything over about 44 inches should have at least 6 inches of clearance. Look at the diagram. It shows how a change to the gas tank shape would dramatically improve clearance.
Pilots should demand this sort of change. Ask about gas tank clearance when you’re buying your paramotor. If there are two sets of motor mounts, you need more prop clearance because the motor would flex more in a fall.
I’ve been told of one other fire incident on launch from a similar cause in England. Here is the forum discussion. To summarize, an experienced pilot fell while forward launching in a way that caused the prop to disintegrate on ground contact. A shard pierced his fuel tank near the cap and a fireball erupted—thankfully, this pilot, too, was rescued by pilots nearby and recovered.
It is obviously EXTREMELY rare but, given the consequence, and how easy it would be to fix, it SHOULD be fixed! The fact is that pilots are going to fall and, now that we know its possible we should collectively take action.
Ideally your paramotor should have clearance (as in the photo above). Either move the gas tank or get a slimmer one.
Something that any pilot might consider is putting either an aluminum/foam (foam towards the gas tank) or lightweight wood protector around the vulnerable parts of their gas tank. This way if any part of the prop tried to puncture the tank, it would hit the protector first and make it much less likely to cause a vapor cloud, even if it does poke a hole in it.
The protector would only need to prop side and down low–not around the whole tank. In a crash everything flexes, from the frame to the prop tips, and it’s surprising how far forward it can come.