Diesel fuel is not very volatile. It's very unlikely (I hesitate to categorically state "impossible") that it could be ignited by a cigarette.
According to my manual, the fuel light goes on when the tank is down to approx 6 litres of diesel.
My Mk3 fiesta did not.
water sensor has malfunctioned/or fuel has large quantity of water contamination.
Diesel engines run on diesel fuel. Gasoline will destroy a diesel engine.
A 1998 Ram with the Cummins diesel has a water in fuel indicator on the dash that will illuminate if there is water in the fuel filter housing.
Where is the water drain for the Water in Fuel light?
Yes, diesel is a bio fuel
Normally that would be the low fuel warning light
If the van has a diesel engine, then you MUST use diesel fuel. Unleaded gasoline will destroy a diesel engine. Diesel fuel is also used as a lubricant in a diesel engine. The use of any other fuel except diesel will result in serious damage. If you have put unleaded in your diesel, do not start or drive this vehicle until you drain the tank and change all the fuel filters.If the van has a diesel engine, then you MUST use diesel fuel. Unleaded gasoline will destroy a diesel engine. Diesel fuel is also used as a lubricant in a diesel engine. The use of any other fuel except diesel will result in serious damage. If you have put unleaded in your diesel, do not start or drive this vehicle until you drain the tank and change all the fuel filters.
Where is the diesel fuel filtered
Water is heavier than diesel fuel
only if it has a diesel engine. A gasoline engine will not run properly on diesel fuel.