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If a Co2 drench system discharged in an engine room of a boat, what are the opinions of fellow safety practitioners:
Is it safe to go in if it is proven that 18% of oxygen is present in the environment or would you wait till it was 21% present?
I know there are other factors such as Co2 will lie in sunken areas as its heavier than air, risk assess etc, but I only want to focus on the % of oxygen at what stage would people say it is safe to enter.
I ask this theoretically as SCUBA say that 18% is the minimum percentage of oxygen needed to support life though there is 21% in the atmosphere.
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"Just enough oxygen to support life" is not the same as "safe to breathe"!
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Carbon dioxide isn't an inert asphyxiant - you'd have to consider its toxic effects as well as the lack of oxygen.
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As I understand it you are correct with the percentage of oxygen in the air being 21% but as the oxygen levels decrease the body is less well able to function and although you could srvive at 18% the bodies faculties do not respond / perform in the same way. So to answer the question adequately we would need to know why someone would wish to enter in to the space with the lower levels, is it to effect a rescue ?
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Some oxygen depletion fire protection systems (designed to prevent fires being able to sustain themselves - i.e. such as in some datacentres), often have the oxygen level set to 18% if I remember correctly. This is considered safe for time limited essential working.
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Oops - my bad - it's actually 15%, so ignore my first post.
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ROCKY
I know else where I have said I would not post again but a number of support messages I have received have partly renewed my faith in this forum so I would offer this for your consideration.
In a past life I was a SCUBA instructor - in the bad old days we used life jackets which operated on their own small compressed air cylinder. In an emergency situation we were taught to bleed a small amount of air into the jacket and then breath the air in an out of the jacket. If my memory was correct we got rid of the air into the water on the third breath. This was because you do not remove all the usable 02 in one breath. But this was in an emergency situation only. Today equipment has moved on and I think this emergency practice as passed.
As such I would not think that entering into an atmosphere know not to contain the "normal" 21 % oxygen at standard atmospheric pressure would be advisable as a standard procedure.
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Kate wrote:"Just enough oxygen to support life" is not the same as "safe to breathe"! lol how can you use quotation marks of something that I didnt write lol I take your point though, I think this is a prime example of goal setting and prescriptive, prescriptive do the absolute minimum, goal setting, achieve higher than the minimum but its reasonably practicable Im looking at I guess as theres lots of losses involved by an inactive boat. NickH yes, limited time working is what it would be, to replace an engine part quickly most likely, they'd be down below, the hatches would be open, mointors with them. Holbrook, no no rescue as such, possibly, maintenance mainly - on fast turn arounds when you need the boat active and time pressures are against the operator. Lots of cash being lost by companies.
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Brian Hagyard wrote:ROCKY
I know else where I have said I would not post again but a number of support messages I have received have partly renewed my faith in this forum so I would offer this for your consideration.
In a past life I was a SCUBA instructor - in the bad old days we used life jackets which operated on their own small compressed air cylinder. In an emergency situation we were taught to bleed a small amount of air into the jacket and then breath the air in an out of the jacket. If my memory was correct we got rid of the air into the water on the third breath. This was because you do not remove all the usable 02 in one breath. But this was in an emergency situation only. Today equipment has moved on and I think this emergency practice as passed.
As such I would not think that entering into an atmosphere know not to contain the "normal" 21 % oxygen at standard atmospheric pressure would be advisable as a standard procedure. Glad you're still posting Brian, Nice one about the life jacket tip. Yes, I know in emergency situations things are all different this really is a cost versus safety (r practicable) thing. I was just wondering about six figure losses being sustained, possibly per day, due to an engine part needing changed rapidly and at what point the call would be made at 18% can support life so people can enter. Possibly Im over simplifying the situation though, it is only hypothetical and your final quote is bang on the money to not enter as a standard procedure.
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Our spec for breathing air for surface use is 21%
Allowing for innacuracies of monitors I would aim for as close to 21% as possible.
Phil
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Rocky
easy for me to say sat here in my nice warm office but 6 fingers is still only money are you insured? Not sure I would go into the area with 18% o2 for that reason. If the part needed changing for a safety critical reason say for example in a chemical factory where not replacing the part could result in a bigger safety risk to the surrounding population than id risk the 18% every time - bit of a spook moment? Or am I just showing my age and poor taste in films there!
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To change a safety critical part why not work in BA, fed from a cylinder on your back, or a big quad on the deck (both are full of lovely 21% O2 containing, dried, filtered air !!)
Phil
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1st clearly finger should be figure
I agree with HeO2 that BA and trained staff would be the best option. But Is BA equipment readily available in the area that Rocky describes or are we adding extra layers of equipment and training that is not practicable? Rocky I did not notice before but you state that the loss would be per day. Once the fire has been extinguished how long would it really take for level to return to 21%? Gases can also be moved in a similar way to liquids so again once the fire is out could a pump not be used to return the 21% levels quickly?
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Yeah, it is only money but people do put the pressure on in those situations. He02, true about the closed BA; prob something to look into though I wouldnt be keen on giving such specialised critical equipment to people who barely use them especially when the pressure is on. I wouldnt want them to make a mistake with the BA.
A few things came together to make that situation on the day, I think we used a dillute air system to force in air and another one to extract gasses present. It worked out fine and people went in with enough o2 just we had a discussion about 18 or 21 % and I wondered what others thought of the situation. Was more of a time thing as we had to get the boat active again.
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Evening Rocky,
I have extensive experience in boat /ship engine room fire suppression gas / drench systems to include steam / halon / CO2 / nebulised water and their after effects. These systems are operated in emergencies or by accidental release. In either event I would recommend that the compartment be treated as a "confined space" as the compartment would be enclosed and there would be a reasonably foreseeable risk of asphyxiation. A standard operating procedure should cover aspects such as purging to atmosphere after release for a given time taking into account the volume of the compartment and the efficiency (volumetric flow) of the vent / extraction system. Should entry be required to recover the compartment after such an event then full BA is recommended, rescue arrangements, comms etc (much to the flavour of the Confined Space regs). Otherwise a competent person must deem the area safe to breathe before normal entry can resume. Bear in mind that the rules do change when out on the high seas!!! I hope this is of help.
Regards, Alex
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16%+ supports life - which is why mouth to mouth works. Below 15% starts to be a risk
At 18% and monitored continuously one could enter but with escape procedures.
21% is regarded as normal atmosphere
Bob
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nickh wrote:Oops - my bad - it's actually 15%, so ignore my first post. I would be very careful when comparing a 15% O2 level within an environment protected by a Hypoxic fire safety system, and a 15% O2 level following a CO2 discharge. The Hypoxic O2 level is constantly strictly controlled by monitoring equipment and software The CO2 discharge environment where the O2 levels are not controlled and the O2 level would only be relevant for that time and the location from where the O2 measurement is taken. The O2 level may vary widely across the space. People walking through an area may disturb pockets of CO2 and reduce the O2 level the level further - and let's not ignore what caused the discharge? If it's a fire, there maybe flammable, toxic or asphyxiant gases and the products of combustion within the space. Anyway, why the rush to re-enter the space? I'd wait for 20 to 21% and not take chances unless BA was available
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Just to throw something else in the mix your monitors (if you have them) will alarm at 19.5% which is there for a reason...
As already alluded to there may be other gases lurking around...so you need to be 100% sure your extraction/ventilation process has worked and you can't confirm that without testing the atmosphere prior to entry.
Below this level the body is starting to do a few things to survive - rate and volume of breathing increase, pulse rate, maintain attention and thinking clearly starts to diminish....much like me on Mondays...
2 guys died last year entering a void space in a barge without a monitor.
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With my 25 years exeperience in SHE in the chemical industry, including a group safety manager for an organisation having 6 sites, 2 of which higher tier COMAH, I would say this:-
NEVER ALLOW ENTRY UNLESS THE AIR IS 21% OXYGEN.
However................IN EXCEPTIONAL CASES eg EMERGENCY SITUATIONS, ENTER WITH SCBA.
By the way confined space entries require a rescue plan regardless of the oxygen or any other level.
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Pikeman wrote:With my 25 years exeperience in SHE in the chemical industry, including a group safety manager for an organisation having 6 sites, 2 of which higher tier COMAH, I would say this:-
NEVER ALLOW ENTRY UNLESS THE AIR IS 21% OXYGEN.
However................IN EXCEPTIONAL CASES eg EMERGENCY SITUATIONS, ENTER WITH SCBA.
By the way confined space entries require a rescue plan regardless of the oxygen or any other level. Good CV doesn't quite beat 4 countries and 26 COMAH/Seveso sites 15 of which top tier...however Confined Space entry rules are that the atmosphere must be above 19.5% and below 23.5 % O2. We also have to be a bit careful here that we don't go a little overboard here (excuse the pun) I assume this is a seagoing vessel(?) and as such the confined space regulations do not apply, that said the principles of protecting those individuals from identifiable risks using good practice should be applied.
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Stevedm how sad that you have seem to have turned this into a bragging match about CVs.
I stated my experience as people often seem to post on this forum based on their opinion, without stating if they have direct experience. I was contextualising my opinion, based on hard experience (also 10 years at ICI, where they knew a bit about confined space entry).
I can find no reference in the regs to an appeptable range of oxygen levels.
I would also restate my position - no entry into oxygen deficient atmospheres except under exceptional cisumstances, and only then with senior management authority. That has always been my position, and that of every chemical works I have encountered.
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I could have made the same comment...However I appologise although mine was meant more tongue in cheek...
Don't disagree with you but to put a figure of 21% on it isn't (in my humble opinion) the right thing to do. Most permits I have come across and training guidance shows that the atmosphere should be above 19.5% and below 23.5% anything below 19.5% requires positive pressure breathing apparatus...
You won't find a reference in the regs as there isn't one...
and it's Friday.....:)
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Ignoring the fact that this forum does not facilitate the use of superscript and subscripts.
The OP asked:
“If a Co2 drench system discharged in an engine room of a boat, what are the opinions of fellow safety practitioners:
Is it safe to go in if it is proven that 18% of oxygen is present in the environment or would you wait till it was 21% present?”
Answer: Entry is permissible when O2 concentration is above 20%.
Rationale:
An O2 concentration below 15 Vol% will lead to a decrease in awareness in healthy human beings, below 10 Vol% to unconsciousness and below 6 Vol% death will occur rapidly.
CO2 concentrations of approximately 29 Vol%, 53 Vol% and 72 Vol% will give rise to these respective O2 levels by displacement.
The IDLH associated with CO2 is 40,000 ppm (4%)
The Specified Level of Toxicity (SLOT) value is given as 1.5*10^40 ppm^n.min. In the case of the engine room in question, the concentration equivalent to the SLOT Dangerous Toxic Load over 1 minute in duration is 105198 ppm (10.5%). At 10.5% CO2, the O2 concentration would be 19%.
Happy New Year
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So we weren't that far away with 19.5%...
:)
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The Code of Safe Working Practices for Merchant Seamen states in para 17.6.6 "A steady reading of at least 20% oxygen by volume on an oxygen content meter should be obtained before entry is permitted."
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stevedm wrote:So we weren't that far away with 19.5%...
:)
No, not too far away, only 35,000 ppm above revised IDLH value of 40,000 ppm :( In reality at 75,000 ppm CO2 (19.5% 02) the CO2 SLOT DTL would require exposure beyond 13 mins.
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Dear all
little anecdote from an ex ICI top tier site man.
I started life as a wet behind the ears Shift Engineer for TI in 1970. Straight in, no safety training, large steel mill with deep pits (house size) full of 1MW DC motors driving 8 stand rolling mills. (Each stand smaller & faster than the previous to reduce steel size) One day shouts of FIRE in pit. Red hot steel slag falling on piles of grease. I attend, no other management about, I instruct operators to discharge first bank of CO2. hugh hissing and white clouds below. County fire arrive, "Not going down there". We don't want water on all our DC motors. Wait..... Co2 seems to be killing the fire... All seems out. "Right , lets go down to see if any residual fire, we'll follow you". So down we go. Get half way doen then hit the CO2. Of course we breathe involuntarly because of rising levels of CO2 in our lungs (O2 >>CO2). So it is sort of fail safe -- you start panting. Back up the stairs pronto.
Many years later end up as a safety manager. Seen it all , done it all.with pragmatic answers
Happy New Year,
Peter
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BS PAS 95 - Hypoxic fire prevention systems for occupiable spaces –
Specification, says that it is possible to work in spaces where O2 levels are as low as 11.1% without any restrictions on the exposure duration. (sorry, have got a copy in front of me, so cannot give full details where in the document it states this, but it's in a table format).
There is, of course, a fundamental difference between working in a tightly controlled atmosphere such as that created by a hypoxic air fire system and that of an uncontrolled atmosphere caused by a CO2 fire system operating & where smoke and products of combustion are present.
11.1% O2 does seem a tad on the low side though doesn't it?
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In the case in question, it is the concentration of CO2 that determines safe entry rather than concentration of O2.
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It sounds very low. And at the surface would result in unconscious or groggy workers!
The only time I'd be happy with 11% O2
Would be underwater, with the remaining constituents of the breathing medium being made up of expensive exotic gasses!
Most training agencies use the figures of 19.5 - 23.5% of O2 in the breathing air as an acceptable limit. I've had a quick literature search, and these are the figures used across the pond too.
I think it would make a lot of sense for the figures to be used in the ACoP so we all have a level playing field.
Comments please!
Phil
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The concentration of oxygen in the blood is logarithmically related to the concentration inhaled. A reduction in the blood/arterial saturation of oxygen can result in a reduced ability to think clearly and a reduction in the time to exhaustion during physical activity.
For a person at rest the maximum reduction of oxygen saturation in the blood due to the reduction in ambient oxygen is determined by:
e (6.8-0.298 x (Inhaled Oxygen concentration))
During escape or during emergency action, physical activity increases and based on the 95th percentile prediction interval, the reduction of oxygen saturation in the blood due to the reduction in ambient oxygen is determined by:
e (10.5-0.455 x (Inhaled Oxygen concentration))
Recoverable saturated oxygen reduction is 10%
Threshold of saturated oxygen reduction leading to harm and fatality is 15%
On this basis and during increased physical activity and atmospheric pressure, the limiting oxygen depletion levels for survivability can be established at 18% and 17% respectively
e^(10.5-0.455*18% O2)
e^(2.31) = 10% SAO2 reduction
e^(10.5-0.455*17% O2)
e^(2.76) = 15% SAO2 reduction
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SBH wrote:I'll sleep better now. mmm..that really made a huge contribution to the topic SBH.... I see nothing changes on this forum then!
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I missed sbh post but I would like to say thanks to all the respondants of this thread, I know there was a bit of negativity in the forum recently about unwelcome posts or negative attitudes though this thread is a great help to me in gaining opinion from clever preople in the safety depts. of UK plc.
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