Scary stuff. RIP to the second poor fellow.

Have to wonder if it's perhaps not a combination event:
1. LPG-powered vehicle - ?leak?, plus
2. Gas emissions inside closed space

Perhaps some combination of gases which could explode easily on vehicle start-up?

Anyway, a thorough venting exercise before vehicle start-up must surely be a first precaution. Have to wonder if some sort of gas sniffer would help?

Very sad.