In the eighties, Ford vans went to plastic fuel lines that were susceptible to falling off when they got warm. Any vehicle that idled with the engine on (direct drive trucks mounts, courtesy vans, ambulances...) could spill fuel and catch fire. Picture ambulances going up in flames in New York City traffic jams.
Not to mention the dual-tank Fords that would recirculate fuel to the wrong tank until it overflowed and caught fire. Rather than fixing the problem, Ford voided warranties on anything that idled in place, and that was the end of getting a
CDS in a Ford.
A friend in the business got t-boned by a girl that ran a stop sign. Hit him right in the external propane tank. Flipped and totaled the van and knocked the tank into the woods, where it hissed propane until empty. No fire, no splosion.
A real stink is added to propane, so if your truck doesn't smell like sewage already it's easy to notice a leak.