Diesel vs. Gasoline vs. Liquid Petroleum/Natural Gas
One can discern two potential safety issues with auxiliary generators: carbon monoxide and refueling risk.
Fuel: Combustible or flammable?
Flammable liquids have a flashpoint of less than 100°F and combustible liquids have a flashpoint at or above 100°F. The rate at which a liquid produces flammable vapors depends upon its vapor pressure, so liquids with lower flash points ignite easier. Fuel will not ignite unless it is a vapor, because the vapor burns, not the liquid itself. With a flashpoint of 52 C (125 F), diesel will not ignite until it is heated to a vapor. Gasoline, on the other hand, has a flashpoint of -43 C (-45 F), which makes it flammable at room temperature.
When it’s in a puddle, a match will not heat diesel fuel sufficiently to burn. Obviously, gasoline and gaseous fuels will ignite readily when uncontained.
So, diesel safer than gasoline, natural gas or LP? Due to the higher flashpoint, I think so. But, as with all fuels, care must be exercised with storage and refueling.
If you expect to run your generator for extended periods of time, it makes sense to look at a separate fuel storage/delivery system which negates the need to manually refuel a hot generator. Similarly, be aware of the risk associated with pooling vapors from spilled gasoline or LP leaks. Also, periodically have your LP/NG generator stall fuel cutoff feature tested. This safety device turns off the supply of gas when the generator speed falls below a certain threshold. Remember, LP falls and will pool against the floor in a room.
The photo here shows an Aurora Generator installation that is off the house. Note that there is no enclosure to capture fumes or impair cooling. The metal roof keeps snow and light rainfall off the equipment. IMO, this is a good clean installation! 😉
Please see the two safety brochures below.