Dry Powder extinguishers are DANGEROUS on yachts.

[Divemaster1]

Despite not being a frequent poster here (we own a 20 something year old grp thingie, with two iron lumps which means most of the time I have to be practical...).

We bought the boat in 2004 in Italy and sailed (or should I say motored) her 12 - 1300 miles home. My worst fears have always been fire onboard and as such we have always had a standing order (conveyed to all visitors) onboard... Fire extingusihers in the cabins are as a escape means only... ie enabeling escape to (relative) safety, so one can set off alarm, seek help, and gain access to more heavy duty fire fighting equipment etc., which practically cannot be located in the cabins. For this above purpose powder is perfectly adequate. If a real fire gets hold on a small boat, getting to an area where an escape is available is paramount. Saving the vessel is secondary to human life! After reaching reletive safety, one may consider to fight the fire with apprpriate means, but not to the detrement of life.

In respect to Engines and electrical systems, my problem with most systems have been a combination of price, practicality and the fact that detection, heat build-up and systems for initiating the extinguishers are somewhat disconnected. Ie you need heat buildup near an often remote extinguisher, or local detector and remote release of gas. Meaning you need a full flood system for both engine and electrical systems (latter often not covered), with a vast over supply of gas and a volume which a lot of boats cannot accommodate.

... until I found a company who facilitates a way to install a system which permitts a flexible system to pull tubing along and across the most probable heat / ignition sources, both electrical and mechanical...... and will release the extinguishing gas at the closest point of heat buildup, whilst indepentently of other power supplys notifies (set of alarm) of extinguisher activationallowing skipper to take appropriate action. Apologies for pointing you to an old MOBO thread of mys installation here...

http://www.ybw.com/forums/showthread.php?t=198749

[oldharry]

Just come back from the annual mandatory Fire Training lecture the government insists we do.

I was astonished to hear the instructor say that Dry Powder exinguishers should NEVER be used in enclosed spaces.

I am no expert, but I pass this on for what it is worth, as I beleive most of us rely on Dry Powder extinguishers.

So the general feeling is clearly that this guy was scaremongering? He claimed to be a time served fire fighter, but I increasingly suspect that he had no experience or training in the marine environment.

Fascinating thread - thanks everyone. keep it coming, its most informative.

[Divemaster1]

So the general feeling is clearly that this guy was scaremongering? He claimed to be a time served fire fighter, but I increasingly suspect that he had no experience or training in the marine environment........

We have to put all these things in context... my guess is that training was done in a onshore industrial/offshore/shipping context...at which point I have to agree... you cannot flood a cabin with powder whilst people sleeping... water mist is correct... as for corridors and often areas with rotational equipment. Electrical areas CO2 or inert gas.... open fuel soures foam....., pipeline fires, cooling is priority ... Gas... keep on supply, cool surrounding area until source can be shut off etc...

Guess is that the context of the training was commmercial and as such answer was given based upon this context .. not small private pleasure crafts.... very different indeed.

[srm]

Just in case anyone gets this far I have seen a few hundred fires put out by dry powder and CO2 extinguishers during Seafish Firefighting courses.

Dry powder knocks the flames out almost immediately, makes operator and observers run for fresh air, leaves a dreadful mess that will damage machinery and electronics, and either sinks through any liquid oil or acts as a wick allowing re-ignition. I have never seen this last point written up but demonstrate it on every course I run.

CO2 does not cool, but puts out the fire by smothering (displacing the oxygen). Once the CO2 disperses the fire is likely to re-ignite so its only effective in a confined space with no ventilation. (Which has to be allowed to cool below ignition point before opening again).

Both CO2 and Dry Powder are dangerous to the operator in a confined space.

Foam is probably the best extinguisher for most situations as it both smothers and cools. We regularly have re ignition after using CO2 and Powder on oil fires but never with foam.

Incidentally, totally enclosing the fire so no oxygen can get in also extinguishes it which is how a fire blanket works.

These observation are based on lighting and letting trainees put out a few hundred fires over 15 years or so.

[Divemaster1]

.......
Foam is probably the best extinguisher for most situations as it both smothers and cools. We regularly have re ignition after using CO2 and Powder on oil fires but never with foam.....

Not intending to take your rely out of context and I would in principle agree... but fire in a boat's accommodation is very rarely an oil fire, but secondary fire as a result of oil or electrical fire spread to accommodation.. key is to stop fire at close source to effect escape... then get out (escape) to alert emergency services, then effect additional fire fighting . From personal experience, foam is very directional ... forms a nice blanket if one know the fuel source of the fire... but if you are disorientated (as in waking up from alams/smoke detectors) other supression units may be more effective enabling escape to safer areas etc.

[ELLIS100]

I see people saying that AFFF is a good boat extinguisher medium, but all the fire fighting courses I have attended have told me that it's not the foam that does the business but a chemical reaction at the barrier of the fuel and the oxygen. Therefore spraying foam on anything other than a liquid layer fire is pretty worthless, unless it's the really high volume stuff used with fire monitors and it's sprayed into an enclosed area.

Apparently the best way to fight a fuel fire is knock it down with dry powder then use your foam, but how many boat fires are fuel fires? Thats how they may start but they pretty much become class A fires really quickly.

[whipper_snapper]

Some interesting and conflicting statements here re carbon monoxide - CO - and carbon dioxide - CO2. A few facts here as I had to learn them as part of my training: CO2 kills by asphyxiation, ie displacing the oxygen the brain and vital organs need to function. It combines with haemoblobin at roughly the same rate as oxygen does, so it is NOT instantly lethal. That's what respiration at its' basic and scientifically correct definition is. You breath in air approx 20% oxygen -O2 - and 0.04% CO2 (and of course, nitrogen, although we'll dismiss that in our discussion). You breath out oxygen approx 16% and CO2 approx 4%, a straight gas exchange (remember I use this kind of meauring equipment every day as part of my job, so I know the numbers). Therefore, we can sort of presume that O2 and CO2 have roughly the same ability to combine with haemoglobin. So when you're exposed to a high level of CO2, respiration depth and rate increase and
you start coughing, that's the signal to move higher, above the level of CO2 (heavier than air). CO, however has 15 times the ability of both O2 and CO2 to combine with haemoglobin..............so one good lung full is the equivalent of 15 deep breaths of CO2 and you don't usually survive, very difficult to reusus someone with CO poisoning 'cos of the amount of carboxyhaemoglobin that has to be got rid of, whereas CO2 can be replaced fairly quickly with oxygen. It's one of the ways we wake people up after anaesthesia, replacing the anaesthetic agent with oxygen. Hope this helps to explain the difference and dangers between CO and CO2.

Ian

Some of what you say there is wrong.

CO2 is not toxic merely by displacing oxygen; CO2 has critical physiological roles. It does not bind to haemoglobin, it is transported by dissolving in plasma. You are correct that CO does bind haemoglobin and that is why it is very toxic.

The physiological roles of CO2 are very interesting, I often think some are good examples of evolution's inherent stupidity.

1stly it affects blood pH and despite heroic buffering capacity, we are tolerant of a narrow range of actual pH. High CO2 levels lower pH which can cause a lot of damage, especially to the brain.

More interestingly, CO2 controls the urge to breathe and this is a lot of the cause of altitude sickness. Bizarrely, blood O2 saturation is not the primary driver of the urge to breather, that is determined by blood CO2 partial pressures and by the closely linked blood pH. If CO2 merely killed by displacing oxygen, then you should be as healthy in an 80/20 CO2/O2 atmosphere as in a normal 80/20 N2/O2 atmosphere. I don't advise you to try it!!

[andygc]

but I do know that inhalation of flour dust is considered a very low health risk.

That'll be apart from exposure to flour dust being one of the commonest causes of occupational asthma?

[VicS]

FWIW the workplace exposure limit for flour dust is 10mg/m³ (8 hour TWA).

[andygc]

I have read through this thread and noted all of the comments on breathing oxygen, carbon dioxide, nitrogen and carbon monoxide.

There is not one posting in this thread on respiration and the effects of O2 and CO2 that is wholly correct. Many contain ludicrous misinformation. I doubt you want a 2,000 word dissertation on respiratory physiology, so I'll just give you a health warning. Don't believe everything you read on internet forums.

My credentials? A career in aviation medicine. (and that you can believe)