Diesel flashpoint?

[john_morris_uk]

I’m wondering if we’ve got any experts on the forums who could give some guidance? I’m currently on a boat where we had a major diesel leak in the engine bay. The secondary filter and water separator on the block of a large Volvo diesel engine had a fault with the O-ring and sprayed 200 or 300 litres of diesel everywhere. We’ve mopped up everything that we can see, but when we now run the engine, there’s a haze of what I assume to be diesel in the engine bay. How dangerous is this? Is it flammable? I’m assuming it’s not explosive. Any suggestions or ideas or guidance as to what we might do? Obviously we will carry on cleaning and the problem does seem to be getting a little better, but is it dangerous?

 

[Sandy]

You can put an oily rag that is well alight on a bucket of diesel and it will not ignite. Demonstrated to me by Somerset and Devon Fire and Rescue Service. You are safe.

Best of luck getting rid of the smell.

 

[Greg2]

I am no expert but remember that during an STCW firefighting course I was mildly surprised to learn that oil poses a far greater risk of igniting than diesel, but that doesn’t make diesel entirely safe of course. Since then I have always been prompt in cleaning up any oil in the engine bay and slightly more relaxed about diesel (not that I leave it there).

That said, a quick search reveals that high flashpoint fluids, including diesel, can ignite at temperatures below their flashpoint.

I don’t think that spilled diesel would create a haze so the question is what is causing it? A fine mist from a leaking joint when the engine is running perhaps? I would be looking for an alternative source to spilled diesel if there is a haze, particularly if the spill has been thoroughly cleaned up.
.

 

[Blue Seas]

Are you at sea or alongside John? And, do you need to run the engine anytime soon?
Check that there are no 'dry' lagging bits (i.e. asbestos pads or equivalent) on or near the exhaust or the turbo - if there are then check that they are not soaked in diesel.
Also, when you say 'sprayed' I assume it was a low pressure leak spray that has since been fixed?
Diesel is pretty safe - as long as it is not atomised or mixed with combustible material (rags, dust etc) which is in turn close to high temp (exhaust bend, turbo as said).
Post a bit more info please.

 

[Momac]

Assuming you are not by now safely moored up somewhere should you not call for assistance?

 

[dunedin]

Be careful with the stuff used for cleaning up the mess. Heard about a recent bad accident when the gasses left over from an intensive cleaning in an engine bay created a flash fire. Very scary. And they were very experience boat people.
The cleaning stuff can be much more flammable than diesel.

 

[sarabande]

I spent some years at BP immediately after the Buncefield fire, but not a full hydrocarbon specialist, just writing response plans.

I have concerns about the "haze" in the engine bay. If it is a diesel mist, then it is likely to be from the pressurised side of the fuel system. Does it disappear when the motor is off , or is there e.g. a rotating thrust bearing soaked in diesel , which causing the mist by spraying centrifugally ?

It's worth reading up on stochiometric ratios as they are significant in the arising of unpressurised explosions/fires. These ratios can vary quite considerably in free surface floods and pressure sprays. B

My mitigation actions would be to remove as far as possible all traces of diesel from the engine bay, and you might consider 2 ways.

One, to use a dispersant (e.g. washing up liquid, or preferably a specific oil spill solvent, plus water and a brush to create a safe emulsion which can be removed from the compartment , though disposal may be a problem unless you can use for example OilTechnics Gold product.

The second is something like lots of catlitter which can be stirred actively around the bilge. It will absorb the diesel and can then be stored temporarily in bags for disposal later.

The test for safety is the nose. If you can smell strong diesel, there is still a source, and every effort to remove it, though cleaning the underside of the sump, or wooden bearers which have absorbed the original spillage, may be difficult.

Safe disposal of detergent diluted diesel or soggy catlitter may be a difficult procedure, but the main objective is to prevent accidental or even spontaneous ignition.

Best of luck.

 

[crewman]

Diesel has a flash point above 55C. Soaked into a porous material it can be ignited at lower temperatures. As a spray it is easy to ignite. I have seen diesel put into a spray bottle (the type that cleaning fluids come in) and sprayed at a candle and igniting. As a bulk liquid (i.e. from a spill) it is quite hard to ignite. I used to work for HSE and was one of the sponsors of the spray ignition research

 

[capnsensible]

Definitely needs fixing.,

Do you remember RN firefighting courses? The instructors used petrol to set diesel on fire in large pans to practice with various types of extinguisher?

Or pretend you are on a submarine.

 

[noelex]

There is no explosion risk, but diesel burns more easily than most yachtsmen realise. At least it surprised me how easy is to start burning it in our Reflex diesel heater.

Drip a little diesel into the tray at the bottom and the diesel can be ignited with small fingernail size scrap of paper and a match. There is no requirement for any accelerant.

 

[S04]

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