VicS
Well-Known Member
What useful and informative post
.
Well it took the total number of posts in the thread to 100.
Dry Powder extinguishers are DANGEROUS on yachts.
- Thread starter oldharry
- Start date
What useful and informative post
.
Well it took the total number of posts in the thread to 100.
whipper_snapper
Well-Known Member
chiefeng
Well-Known Member
Co2
Some wise words from SRM.
Co2 is really only effective in small and totaly enclosed spaces, and only then if the source of ignition or fuel can be eliminated. If you are using it in the engine room then you really should shut/block off all ventilation and ensure the bilges are sealed or the CO2 will find it's way out of the space you are tying to flood also ensure you have overcapacity in the CO2 tank to cope with the losses.
Dry powder, as far as I remember interferes chemically with the flame chain reaction to put out a fire.
If it's a cooker pan fire then use the fire blanket you should have within easy reach.
For anything else get a bucket and use the most abundant and effective medium available for putting out fires. Water.
One of the first things on the my list of priorities if I discover a fire is turn the engine fuel off and isolate the batteries (both within easy reach).
Hopefully any fire would be in it's early stages and therefore small and could be dealt with easily.
If it's a raging inferno then you are too late anyway, the chances of being able to put it out with an extinguisher is minimal.
High pressure water systems are very effective as they smother and cool the fire as the mist is sucked into the flames by the air flow. A Kartcher HP washer has the same effct as long as you don't direct the flow directly at the flames (the velocity of the water droplets tends to blast the fire in all directions if you are too close!!)
That's my two penny's worth. FWIW.
Rgds
Bob
Some wise words from SRM.
Co2 is really only effective in small and totaly enclosed spaces, and only then if the source of ignition or fuel can be eliminated. If you are using it in the engine room then you really should shut/block off all ventilation and ensure the bilges are sealed or the CO2 will find it's way out of the space you are tying to flood also ensure you have overcapacity in the CO2 tank to cope with the losses.
Dry powder, as far as I remember interferes chemically with the flame chain reaction to put out a fire.
If it's a cooker pan fire then use the fire blanket you should have within easy reach.
For anything else get a bucket and use the most abundant and effective medium available for putting out fires. Water.
One of the first things on the my list of priorities if I discover a fire is turn the engine fuel off and isolate the batteries (both within easy reach).
Hopefully any fire would be in it's early stages and therefore small and could be dealt with easily.
If it's a raging inferno then you are too late anyway, the chances of being able to put it out with an extinguisher is minimal.
High pressure water systems are very effective as they smother and cool the fire as the mist is sucked into the flames by the air flow. A Kartcher HP washer has the same effct as long as you don't direct the flow directly at the flames (the velocity of the water droplets tends to blast the fire in all directions if you are too close!!)
That's my two penny's worth. FWIW.
Rgds
Bob
kesh
Well-Known Member
to criticize without offering anything is very poor manners. and pretty useless.
why not give us that dissertation?
whipper_snapper
Well-Known Member
I don't have a career (or even a weekend) in aviation medicine, but I can claim a credential that may be unique here:
I have witnessed several deaths due to exposure to very high CO2 concentrations. Collapse and total unconsciousness was essentially instantaneous. It was not mere suffocation. I don't know how long after that death followed, but presumably it did not take long.
I have witnessed several deaths due to exposure to very high CO2 concentrations. Collapse and total unconsciousness was essentially instantaneous. It was not mere suffocation. I don't know how long after that death followed, but presumably it did not take long.
maxi77
Well-Known Member
Well that is very helpfull, some of this stuff is wrong but I won't tell you which bits. You might as well have saved yourself the trouble of posting
Heckler
Well-Known Member
Correct
Stu
Heckler
Well-Known Member
Carbon monoxide does this not carbon dioxide
Stu
whipper_snapper
Well-Known Member
Sorry, but that is not correct. You think I didn't know what I was seeing ?!
I don't know how fast very high concentrations of CO kill, but I can assure you that very high concentrations of CO2 knock down almost instantly. The biology of the interactions of the two gases with the human body are completely different, but the myth that CO2 only suffocates is just that, a myth.
kesh
Well-Known Member
i think we all know CO2 has toxic effects, the argument is how toxic. one breath cyanide like death has been claimed and disputed.
i wonder if the person claiming this has witnessed CO2 acting alone, or in a situation like a fire where CO2 and CO are present (and heaven knows what else) and oxygen absent.
the internet seems to only have info that 8% CO2 causes unconsciousness in 5 or so minutes. though i haven't done a thorough search.
i wonder if the person claiming this has witnessed CO2 acting alone, or in a situation like a fire where CO2 and CO are present (and heaven knows what else) and oxygen absent.
the internet seems to only have info that 8% CO2 causes unconsciousness in 5 or so minutes. though i haven't done a thorough search.
andygc
Well-Known Member
Thanks for the brickbats. I was too busy earlier, but as you asked, here’s the short version:
The transfer of oxygen from atmosphere to tissues depends on binding with haemoglobin (Hb). That binding is described by a graph, the oxygen dissociation curve. The curve relates the partial pressure of oxygen in alveolar (ie lung) gas or body fluids to the saturation of Hb binding of oxygen. The graph shifts to left or right, depending on the pH of blood. Decreasing pH (acidification) shifts it to the right, which means Hb releases oxygen. Increasing pH (alkalisation) shifts it to the left, which means Hb binds more oxygen.
In simple terms, the rate and depth of respiration are controlled primarily by the level of CO2 in the blood (hypercapnic drive). This is a good thing. CO2 is what you make when you use energy, respiration is how you get rid of it.
When you are in an oxygen depleted environment you add hypoxic respiratory drive, that is, the low level of oxygen in the blood is detected and respiratory effort increases. This reduces CO2 levels in the lung and pulmonary circulation, makes the blood there more alkaline and shifts the dissociation curve to the left – thus binding more oxygen. This is another good thing. In the tissues, where work is done, CO2 levels are higher. Capillary blood is more acidic than arterial blood. The dissociation curve shifts to the right. Hb releases oxygen to the tissues. This is another good thing. In the atmosphere in which we live this system works well. It works well in people who normally live at sea level up to about 10,000 feet above sea level. This system for controlling respiration allows man (and animals) to live in a wide altitude range despite substantial variations in atmospheric pressure. It is most definitely not an example of evolution's inherent stupidity.
Carbon monoxide binds preferentially to Hb. That is, it is bound much more strongly than is oxygen. If there is sufficient CO to block O2 uptake, you die. It is potentially lethal at quite low concentrations. There is a Wikipedia article that gives the figures.
Carbon dioxide is not toxic. That is, it is in no way poisonous. Forgive me if this now gets technical, but I don’t feel like rewriting something I wrote elsewhere. sats=oxygen saturation, minute volume=the volume of air shifted by the lungs in one minute
If you breathe a CO2 enriched atmosphere you will stimulate the hypercapnic drive of respiration. Normal air is effectively 0% CO2. Breathing 2% gives an increase of about 25% in respiratory minute volume, and increases alveolar pCO2 by a couple of mm. Thus, a trivial effect on pO2. Breathing 4% CO2 doubles the respiratory minute volume and brings the alveolar pCO2 up to about 44 mm, so again only a small decrease of pO2. Even with the rightward shift of the dissociation curve due to the slight acidosis, you are still well up on the plateau (the top of the curve is almost flat – another good thing) with a haemoglobin saturation close to normal. Breathing 6% CO2 the minute volume almost quadruples, but the alveolar pCO2 only gets to about 50mm, which would mean a drop in pO2 to 93mm and sats should still be up at 94-95%. You have to have inhaled CO2 above 7% before things go badly wrong.
When you stop breathing CO2 enriched air the return to normal respiratory rate is rapid - it take only a few breaths to get the arterial pCO2 back to normal. CO2 has no toxic effect on gas exchange in the alveoli.
If you remain in an atmosphere with CO2 levels above 7% you will rapidly become exhausted by respiratory effort whilst being significantly hypoxic.
Although whipper_snapper may not have got everything straight, he was dead right about CO2. If you are in an atmosphere with high concentrations of CO2 you will die, and do so quickly. For skipper_stu, indeed CO can do this, but so can CO2. The difference is that for CO you only need a low concentration (1.28%), whereas for CO2 you would need a much higher concentration.
If somebody knows the STP equivalent volume of CO2 in an extinguisher and the volume of the boat cabin they want to use it in, they should be able to work out the likely CO2 concentration when the extinguisher is fired.
The transfer of oxygen from atmosphere to tissues depends on binding with haemoglobin (Hb). That binding is described by a graph, the oxygen dissociation curve. The curve relates the partial pressure of oxygen in alveolar (ie lung) gas or body fluids to the saturation of Hb binding of oxygen. The graph shifts to left or right, depending on the pH of blood. Decreasing pH (acidification) shifts it to the right, which means Hb releases oxygen. Increasing pH (alkalisation) shifts it to the left, which means Hb binds more oxygen.
In simple terms, the rate and depth of respiration are controlled primarily by the level of CO2 in the blood (hypercapnic drive). This is a good thing. CO2 is what you make when you use energy, respiration is how you get rid of it.
When you are in an oxygen depleted environment you add hypoxic respiratory drive, that is, the low level of oxygen in the blood is detected and respiratory effort increases. This reduces CO2 levels in the lung and pulmonary circulation, makes the blood there more alkaline and shifts the dissociation curve to the left – thus binding more oxygen. This is another good thing. In the tissues, where work is done, CO2 levels are higher. Capillary blood is more acidic than arterial blood. The dissociation curve shifts to the right. Hb releases oxygen to the tissues. This is another good thing. In the atmosphere in which we live this system works well. It works well in people who normally live at sea level up to about 10,000 feet above sea level. This system for controlling respiration allows man (and animals) to live in a wide altitude range despite substantial variations in atmospheric pressure. It is most definitely not an example of evolution's inherent stupidity.
Carbon monoxide binds preferentially to Hb. That is, it is bound much more strongly than is oxygen. If there is sufficient CO to block O2 uptake, you die. It is potentially lethal at quite low concentrations. There is a Wikipedia article that gives the figures.
Carbon dioxide is not toxic. That is, it is in no way poisonous. Forgive me if this now gets technical, but I don’t feel like rewriting something I wrote elsewhere. sats=oxygen saturation, minute volume=the volume of air shifted by the lungs in one minute
If you breathe a CO2 enriched atmosphere you will stimulate the hypercapnic drive of respiration. Normal air is effectively 0% CO2. Breathing 2% gives an increase of about 25% in respiratory minute volume, and increases alveolar pCO2 by a couple of mm. Thus, a trivial effect on pO2. Breathing 4% CO2 doubles the respiratory minute volume and brings the alveolar pCO2 up to about 44 mm, so again only a small decrease of pO2. Even with the rightward shift of the dissociation curve due to the slight acidosis, you are still well up on the plateau (the top of the curve is almost flat – another good thing) with a haemoglobin saturation close to normal. Breathing 6% CO2 the minute volume almost quadruples, but the alveolar pCO2 only gets to about 50mm, which would mean a drop in pO2 to 93mm and sats should still be up at 94-95%. You have to have inhaled CO2 above 7% before things go badly wrong.
When you stop breathing CO2 enriched air the return to normal respiratory rate is rapid - it take only a few breaths to get the arterial pCO2 back to normal. CO2 has no toxic effect on gas exchange in the alveoli.
If you remain in an atmosphere with CO2 levels above 7% you will rapidly become exhausted by respiratory effort whilst being significantly hypoxic.
Although whipper_snapper may not have got everything straight, he was dead right about CO2. If you are in an atmosphere with high concentrations of CO2 you will die, and do so quickly. For skipper_stu, indeed CO can do this, but so can CO2. The difference is that for CO you only need a low concentration (1.28%), whereas for CO2 you would need a much higher concentration.
If somebody knows the STP equivalent volume of CO2 in an extinguisher and the volume of the boat cabin they want to use it in, they should be able to work out the likely CO2 concentration when the extinguisher is fired.
Ricd
Well-Known Member
Ditto...instantaneous knock down...
Ricd
Well-Known Member
If somebody knows the STP equivalent volume of CO2 in an extinguisher and the volume of the boat cabin they want to use it in, they should be able to work out the likely CO2 concentration when the extinguisher is fired.[/QUOTE]
But..CO2 is about 1.5 times more dense than air or CO. It will not necessarily ventilate from below decks once it has done its job and extinguished the fire and will flow to lower levels where it could present a significant hazard to the unsuspecting. Lots of reported cases death due to volcanic CO2 accumulating in depressions.
But..CO2 is about 1.5 times more dense than air or CO. It will not necessarily ventilate from below decks once it has done its job and extinguished the fire and will flow to lower levels where it could present a significant hazard to the unsuspecting. Lots of reported cases death due to volcanic CO2 accumulating in depressions.
VicS
Well-Known Member
Well thats pretty easy to work out
RMM of CO2 is 44 so 44grams have a volume of 22.5 litres at STP, Call it 24 litres at ambient temperature.
A 1kg extinguisher therefore contains 24 x1000/44 = 545 litres or 0.55 cu m.
What's the volume of a modest sized boat cabin ... if the boat is large enough to be carrying a 1 Kg CO2 extinguisher ( they are not exactly pocket sized things)..... 10 cu m ??
0.55 cu m into 10 cu m ... 0.55/10 x100 = 5.5 %
A bit lower than the 7% which Andygc suggests is the point above which things go badly wrong.
Conclusion:
1Kg into a small boat cabin, or 2k g into a more generous sized cabin would very be dodgy
Check my arithmetic, make you own estimate of your cabin volume and see how it works out.
.
whipper_snapper
Well-Known Member
Thanks, because I am a bit thick could you explain where I did not get everything straight ?
I am struggling to reconcile: "Carbon dioxide is not toxic. That is, it is in no way poisonous. " with the para that follows.
You show that even a few % CO2 has a significant physiological effect, and that levels over 7% start to become dangerous. Since we live in 80% inert gas, how can a gas that affects physiological state at a few percent and becomes life threatening above 7%, be considered non toxic?
However, regardless of disagreements over the meaning of a word, the key point is that CO2 kills not merely by reducing oxygen levels in the air we inhale.
whipper_snapper
Well-Known Member
Pure CO2/clean air. Hard to say the ratio, but very high. Perhaps 70:30. Obviously oxygen levels proportionally lowered as a result.
I expect the other person who has witnessed this knows exactly the circumstances I am describing - it seems I can't even claim to be the only one with such experience, what a group!
planteater
Well-Known Member
Wow. I've never heard of this. I always imagined that walking into a space full of CO2 would be like walking into a space full of nitrogen or a hard vacuum - a slow suffocation.
But then the "gasp" response is triggered by CO2 buildup so I guess discomfort and panic might be the result - but instant knockdown?
Ricd
Well-Known Member
My experience was regarding an investigation into use of CO2 for dis-infestation. The precautions necessary to safeguard personnel entering way outstrip those necessary for conventional fumigants - the reason was the instant knock down (one breath) and difficulty in re-sus, assuming there is somebody around wearing fully breathing kit to enter and bring out the body! Having said all of that there is load of stuff about volcanic CO2 causing instant death. My understanding is that the issue is asphyxiation and toxicity. From "memory" it was explained to me that at high concentrations CO2 does displace O2 in Haem irreversibly (but it was 15 years ago and my memory could be failing).
Ricd
Well-Known Member
y the way...I agree with wipper-snapper...WHAT A GROUP!
vyv_cox
Well-Known Member
Once when touring a distillery outside Aberdeen I was invited to put my head inside one of the reacting drums, which had a moderate level of CO2 plus air inside it. It had one hell of an effect on me, definitely not 'slow suffocation'. Absolutely unbreathable. I can imagine that in higher concentrations it would be a very serious situation.
