SteveBarnsleytrucker:
In Diesel engines I think it’s how the fuel mixture mixes with the air that makes the spark am I right?
diesel as such self ignites when the mixture is compressed and heats to the point of ignition, that’s why diesel engine compression ratio is a lot more that petrol. 
When you are pumping diesel into your tank there is always a fine mist/spray of fuel and air present. Remember a truck filler is open unlike the snug fit of a cars filler. Theoretically if your night heater is on this mist could be drawn into the inlet and ignited. 
A quick, if dodgy, fix on the road for a dicky night heater can be to get it fired and blast a shot of something flammable like WD or easystart up the inlet to “clear out” the combustion chamber and plug. You’d be surprised he much flame can come from the exhaust of the heater 
Much safer if you use compressed air though
Personally I’d say the bigger risk would be in air locking the heaters fuel line by filling up with it switched on 
Never thought about an explosion risk, I just presumed it said switch off heater when filling to prevent sediment or air being sucked up by the heater pump.
When you pump fuel into a tank the air that is displaced by the fuel has to escape somewhere, on a truck this is back through the filler pipe but on a car it’s usually the tank breather pipe. The escaping air will also carry a fine mist of fuel, and with petrol even a tiny spark would ignite it.
In the USA I noticed that most pumps had a vapour recovery system which ■■■■■ the air from the tank as you add fuel, the vapour in the air is recycled back to the storage tank so effectively the fuel you get could have been in your tank before!! This is a safety feature, I guess in the heat of the Arizona desert petrol fumes could easily self ignite.
I am not sure if this system is fitted to diesel pumps as I have only driven petrol cars in the USA recently.
The rubber boot in the US was more an environmental thing to do with air pollution hence why they were needed/mandated more in certain low air quality areas. They’re not legally required anymore as most cars have one built in. 
It never bothered me, I used to run my night heater 24/7 in colder months. Filling up at diesel pumps that are away from petrol pumps presents no hazard, it does not give off explosive fumes, in fact you could hold a lighted match over the open filler cap on a tank and nothing would happen.
Regulations here are lapse to the point of a joke Staff at petrol stations are banned from smoking inside the shop but can quite happily sit a few feet from the pumps and smoke away to their heart content and not a word would be said if someone used a phone when filling up.
SteveBarnsleytrucker:
Petrol has a higher flash point than diesel.
Petrol has a lower flashpoint than Diesel.
dieseldave:
SteveBarnsleytrucker:
Petrol has a higher flash point than diesel.Petrol has a lower flashpoint than Diesel.
Sorry my bad. it was one or the other 
It’s all a bit over the top. Based on that theory,why don’t petrol cars have spark arresters on their exhaust when on a forecourt?