dieseldave:
Carryfast:
Edit to add
hse.gov.uk/research/rrpdf/rr1107.pdf
Have you actually read the document you’ve linked?
Have you actually read my post made at 6:59 above?
Remembering that we’re speaking of the environment of the engine room (including all conditions such as fuel system pressures etc) of a narrowboat it looks like you’ve provided support for what I said. Thanks for that. 
As usual, your googling and posting of off-topic and irrelevant ‘facts’ has been spotted for what it is, …an unsuccessful attempt to muddy the waters.
Carryfast:
As I read it it’s just rightly saying that a fine fuel mist ain’t the same thing as a pool of diesel on the floor or a leaking unpressurised pipe regardless of whether it’s a ship engine room or a river boat. 
I’d agree with that, because it’s essentially what I wrote in my first post.
That’s why I struggled to see the relevance of mentioning any other kind of vessel/engine room when the topic is about narrowboats.
In the environment of a narrowboat engine room, there’s hardly likely to be much pressure in the ‘feed’ side of the system. If that leaked, it would end up as a pool on the floor.
On the other hand, the ‘pressure’ side of the system eg: from the pump to the injectors is under a much higher pressure. A leak in this part of the system could easily result in a fine mist spray. However, three things must all be present at the same time in order to have a fire/explosion in the likely circumstances to be found in the engine room of a narrowboat. I’d still say that this is hardly likely in a narrowboat engine room as I said in my first post.
1.) atomised diesel at a temperature in excess of its flashpoint (> 65 degrees C)
2.) a fuel/air mix within the right proportions (1% - 5% for diesel)
3.) a sufficiently hot heat source in excess of the AIT figure for diesel ( >230 degrees C or thereabouts)
Carryfast:
Anyway I’ve admitted that it’s a pointless comparison and maybe diesel is arguably safer than petrol.But I’m probably not the only one who’s thinking along the lines of going from diesel to LPG to avoid the costs of white diesel.In which case the obvious solution would be to allow the use of red diesel in boats on grounds of safety.Problem solved.
I agree with your conclusion about red diesel on the same grounds that you’ve mentioned.
Now for your mention of LPG. (I imagine you’re speaking of Propane??)
I’d suggest that an LPG leak on either side of the system is potentially very dangerous, so (personally) I’d not consider using LPG.
LPG is usually at a pressure of around 8bar (120psi) in carriage and storage, but then there’s normally a pressure reducer in the system that takes the gas to the appliance that actually uses/burns it.
Typical flammable range for LPG is in the order of 2% - 10%, which IMHO would easily be possible in confines of the engine room of a narrowboat, even if the leak were from the lower pressure side of the system.
I’d discount the use of petrol too for the reason that any petrol leak will form an ignitable mixture (1% - 7%) with air if the temperature is higher than minus 40 degrees C, so in the real world, petrol is always dangerous and potentially lethal within the confines of a narrowboat engine room.
The surprising thing about petrol is the highish AIT figure of 380ish degrees C, but this does vary according to formulation.
Just for completeness, the vapours of evaporated Petrol and Diesel as well as leaked (reverted) LPG at zero pressure are all heavier than air.
