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Question on Carbon Monoxide

Discussion in 'Compressors, Boosters and Blending Systems' started by Phil_C, May 23, 2012.

  1. Phil_C

    Phil_C ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: UK, Middle East, Cyprus
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    Hi folks - looking for advice from someone knowledgeable about petrol (gasolene) compressors as opposed to electric motor driven ones.

    I have just bought a BAUER PE100 (petrol) and filled a couple of tanks from it. It was very noticeable that (as you would expect) I could smell the exhaust fumes from the motor as I was stood near the compressor,so I decided to test the final tank fill for CO levels.

    The sensor I used (an Analox CO EII) gave a reading that fluctuated between 0 and 1 parts per million CO, so was I suspect reading a trace of carbon monoxode in the breathing air in the tank.

    The compressor was operated outdoors, in a slight breeze, with the extended air intake fitted, so was right within how BAUER say it should be operated. The analox sensor did not fluctuate in the open air, only when sampling from the tank. So I guess my question is, how normal is it to detect a trace of CO from a cylinder filled from a petrol compressor, and what is a safe/normal limit to expect it to read.

    I am going to drain the tank down and refill it again making religiously sure that all possible steps to prevent CO being drawn in are followed.

    I cant see anywhere where it says what to expect - is it a case of no CO at all, or is 1 ppm not a reading worth bothering about?

    Cheers

    P
     
    Last edited: May 23, 2012
  2. bleeb

    bleeb Photographer

    # of Dives: 100 - 199
    Location: Ottawa, Canada
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    Since you have your own CO tester, maybe you've already seen this thread, but if not, it includes some discussion on CO limits: CO tank risks and protections

    The topic of how much is too much periodically comes up here on Scubaboard. I think one of the reasons it keeps coming up is because it's a soft limit, and depends on environmental conditions, how much you're diving, how deep you're diving, how long, etc. As has been suggested in other threads, the risks of low-level exposure may not be so much in the rapid onset of toxicity or unconsciousness that is normally associated with CO poisoning. For diving, it could be more the partial loss of cognitive abilities resulting in being able to react adequately to problems or emergencies.

    All that being said, my non-expert perception is that 1 ppm in itself is not much to worry about. Your instincts seem likely to be correct to me, in that zero in open air and almost 1 in the tank mean the amount in the tank is likely to be non-zero. The concern may be more that the presence of any compressor-generated CO in the output could also mean the presence of far nastier hydrocarbons or other combustion byproducts in the breathing gas. You may not be looking at exhausts being sucked in the inlet, and it's suggestive that something inside the compressor that something inside the compressor isn't quite working as well as it should, may be intermittently failing, or be nearing the verge of complete failure (i.e. seals, catalyst saturation or breakthrough, lubricant flashover, etc.).
     
  3. Phil_C

    Phil_C ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    Location: UK, Middle East, Cyprus
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    Hi Bleeb - thanks for your thoughts - I hope you are not right in your second paragraph! the compressor is brand new and straight from the manufacturer and had just got commissionig hours on it (about 30 minutes testing etc at BAUER UK last week when they unpacked it).

    I hadn't seen the link you posted so thanks for that, I'll have a look through. I know it is a case of how long is a piece of string, a bit like depths at which people get narc'd and so on, but I hadn't seen any advice abotu what was normal or what to expect in relation to CO, and the analox manual doesn't help on that score.

    P
     
  4. iain/hsm

    iain/hsm Manta Ray

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    Phil.

    What's gasoline…………some sort of hand cream I guess?

    The real critical factor your must understand here is not the 1ppm number on the dial but the type of filter cartridge your using
    and the air temperature your running in.

    If A. Your using a standard molecular sieve and carbon filter cartridge then 1ppm is perfectly OK in fact its very good for a
    petrol driven compressor with an extended air intake hose and no wind conditions.

    And in all honesty I'm surprised it's so low, without a catalyst.

    However (and here's the kicker) if B. Your using a cartridge WITH a catalyst chemical to convert carbon monoxide
    into C02 such as hopcalite then things get a tad more complicated.

    1ppm then shows only the breakthrough, the amount that gets past the catalyst, and the "true" reading could be as high as the typical "killer" range of 50ppm.

    One reason why (I thought) in Europe under the British Standards BSEN8478 and 12021
    we used a second independent filter tower filled with pure Hopcalite and "purity protected" by an in line visual purity moisture vapour indicator downstream of the primary filter and upstream of the secondary Hopcalite filter on petrol driven compressors.

    For Breathing Air in Europe use BS EN12021:1999 The maximum level for carbon monoxide was 5ppm but this is difficult to maintain in oil lubricated high pressure compressors and with a petrol engine the maximum now is 15ppm.

    Let us know the brand and model of compressor and the filter cartridge part number also the ambient air temperature your testing in. Iain Middlebrook
     
  5. Phil_C

    Phil_C ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: UK, Middle East, Cyprus
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    Iain - I thought that I would try to translate our 'English petrol' for the bulk of the users of SB who seem to be from across the pond (from our perspective) :)

    I'm afraid i don't know what type the filter is - but the compressor is a new (as in 2012 model) BAUER Poseidon PE100 TB. I'll have a look and see if the manual says what sort of filter etc it has.

    - Manual states - "A dry micronic filter is used to filter intake air"

    4.4.4. FILTER SYSTEM P11 DESCRIPTION
    The air leaving the final stage is cooled in the after-cooler to approx. 10 - 15 °C (18 - 27 °F) above ambient temperature
    and then enters filter system P11 with TRIPLEX longlife cartridge (Fig. 19).

    The filter assembly consists of separator and cartridge chamber. In the separator surrounding the cartridge
    chamber liquid oil and water particles are reliably separated from the compressed medium.
    Residual oil and water vapors are then removed by the TRIPLEX longlife cartridge. The quality of the breathing air
    produced conforms to DIN EN 12021.

    It also says -

    On compressor units with petrol engines only use cartridge, part no. 059183 to dry, de-oil and remove CO.
    Filling weight: 217 g; Saturation weight 229 g.
    Example: at an ambient temperature of 20°C, 31 to 38 10-ltr-bottles can be filled with this cartridge, which is
    equivalent to between 10 and 13 operating hours at a filling pressure of 200 bar

    Which suggests the cartridge is designed to remove CO as well.

    Cheers

    P

    ---------- Post added May 23rd, 2012 at 07:27 PM ----------

    By the way the unit is in the UK - so at the moment temperature is anything between 6 degres and 25 celsius changing daily !!
     
  6. iain/hsm

    iain/hsm Manta Ray

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    I think we confuse them enough with Aluminium, spanners and bank holidays.

    Now if I'm correct the Bauer triplex 059183 cartridge in USA is called for the
    P0 filter. Here in UK we use it in the P21 using a 059183-410 cartridge.

    The P11 to me is a much more dangerous animal used with the LAR-V

    From what you say in the manual the Bauer P11 filter I assume uses the same cartridge
    as the P0 and P21 So I am more convinced now that your 1ppm reading is due to the catalyst
    working and not a reading off say Tower Bridge London in a heat wave and rush hour.

    Enclosed for comparison as its an American web site are the NEDU
    reports for the Bauer unit electric and Petrol (gas) to show the difference
    I have tried to get as near to your 1ppm starter (on electric) and petrol engine.

    The thing to look for is the one (1) hour test and the 25 hour test
    On the electric K280 the CO starts at 1.2 ppm and rises to 4.3ppm there is no C0 removal just
    showing the CO generated by hot oil breakdown over 25 hours
    Pump Rotation Speed 1320 RPM test Discharge Pressure 4700psi

    Bauer K280 Electric No CO removal
    1hour 1.2ppm
    25hours 4.3ppm

    On the petrol driven 2 cfm Varius this used your same cartridge with CO removal.
    Just note that the results show a 50 hour test so the filter cartridge was change for a new one
    at the 25 hour interval. Hence why the readings improve.

    The test report shows at one hour CO is <0.5ppm and at 25 hours its 8ppm after the cartridge
    change at 26 hours with new cartridge its back to 1ppm and at 37.5 hours 14.3ppm. So you can
    see both the degrading of the chemicals ability over time and also the heating effect due to oil
    over extended running on a small fast running compressor adding to the production of CO
    Pump Rotation Speed 2600RPM Test Discharge Pressure 3000psi

    Bauer Various Petrol with P0/P21 filter and CO removal
    1 hour 1ppm
    25 hours 8ppm
    37 hours 14.3ppm

    Just to be a little controversial for comparison I have enclosed also the NEDU on the RIX 4VX
    oil free compressor tested without any filtration whatsoever
    To be fair compare it with with the electric driven K280
    No oil, No filters, only water separators, and no chemicals.
    Pump Rotation Speed 750RPM delivery 30 cfm Test Discharge Pressure 5000psi

    CO levels were:
    1hour <0.5ppm
    25 hours <0.5ppm
    50 hours <0.5ppm

    It's American designed in California see what the sunshine state engineers can do when
    there not on the beach. Just don't tell them in the UK we do better electrics.

    Enclosed Navy Experimental Diving Unit Reports

    1. Evaluation of Bauer K280.75 http://www.dtic.mil/dtic/tr/fulltext/u2/a242085.pdf

    2. Bauer Petrol Varius: http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/4870/ADA304678.pdf?sequence=1

    3. NEDU of Rix 4VX AIR/NITROX: http://www.dtic.mil/dtic/tr/fulltext/u2/a304678.pdf

    Iain Middlebrook
     
  7. Phil_C

    Phil_C ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    Thanks Iain - gives me a better idea what sort of levels are 'acceptable'.

    I guess I am going to be checking the CO on all tank fills from the compressor and keeping track of how it is doing. The filter will then get changed out at the manufacturers intervals unless the CO ppm goes up significantly in the meantime.

    Looking at BS 12021 they seem to suggest that 15 ppm is the new acceptable limit, so i will monitor my levels and see how things go.

    By the way if you work with compressors do you know where I can get a Coltri MCH6 looked at in the north London/Midlands area. I have a single phase electric Coltri which has very low hours on it (about 4 or 5), but had stood idle for a (long) while before I acquired it. It still looks brand new - no rust etc. has had a new filter and oil change, but after about 6 tank fills has started blow the RCD or fuse after it has been under pressure for a minute or two.

    Sorry to be a pain - Cheers - P
     
  8. iain/hsm

    iain/hsm Manta Ray

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    Not everyone agrees with breathing 15ppm of carbon monoxide, most in the profession think going
    from the old 5ppm to the new 15ppm it's a backward step.

    IMHO seeing 5ppm is a poor sign of purity but the maximum you want to be comfortable with.
    Granted few do deep air nowadays so the PPco at depth is small but significant non the less.

    Notice those NEDU reports I linked, the US Navy don't mess around yet they allow 20ppm,
    I found that strange at first.

    Then found with in line "real time" continuous analysis you could get away with it.
    But with our UK 3 month test in arrears then 12 weeks of blind filling before the next test?
    No way in my book. But then again I'm the oil free guy LOL Iain Middlebrook
     
  9. iain/hsm

    iain/hsm Manta Ray

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    On the little Coltri. That's a different question, Ray's your man on here for Coltri
    But a fuse blow after a minute running I doubt there is much pressure or rod load
    so my first poke would be that the motor connections are loose or in the DOL direct
    on line connections, one or all of the wires being loose. Helps to know if 3 phase
    or 1 phase and all the motor plate details but a loose wire would be my first cheap shot.

    If its say running more than a minute and developing pressure say 150 plus bar 2000psi
    an it overloads then it's a tad trickier.

    I guess you don't know what each interstage pressure is, but is there air reliving out of
    any of the relief valves? The overload on these little pumps is very close to maximum
    running load so any blockage of a discharge valve say will increase the interstage
    pressure to a point that the relief valve opens and the BHP required increases pro quo.

    Most professional compressor motors are chosen and rated for the BHP required at the
    high end relief valve setting not at the low end maximum working pressure,
    With these small portables it's the low cost price that counts so most bang for your buck
    smallest motor rating driving the highest load pressure and flow.
    If your single phase UK that only 13 amps FLC hardly enough to drive at 2cfm and 230 bar

    The motor overload on a relief valve can be as much as 20% more load on the drive motor
    than the developed max pressure, in which case the weak link is the motor overload or
    fuse before the relief valves open.

    Hence why knowing each of the interstage pressures is important.

    Running "offload" ie with the filling whip venting off to atmosphere and she runs but when
    you close down the filling whip and she overloads is a better sign of motor overload or
    loose electrical connection. An ampere clamp meter helps too

    There is worse to come with rods and pistons. Leaving a pump for a long period of time
    rust can develop on the piston liner and stick a floating head piston (or valve) TDC
    top dead centre. If in the lower ends say 1st or 2nd stage the piston can seize in the
    liner and the rod loading goes off into orbit, either the motor overloads (good) or
    the con rod snaps (bad) but your still running so I don't think your at that point unless
    its got a floating final stage.

    As for anyone doing then in your part I haven't a clue, I would do it yourself Im sure
    there are others on the forum who can take you through a little Coltri stripdown. Iain Middlebrook
     
  10. Zodiacdiverdave

    Zodiacdiverdave Solo Diver

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    Phil, relax and go diving. your levels are fine. make sure you keep your analox calibrated, filter fresh, change your oil as required by Bauer, and make sure your intake is up wind. If you use a long intake hose make sure the hose has an over sized diameter. Bauer recommends 1\4 in oversize for every 10 feet.
    Canada's max CO level is 5ppm. USA is 10ppm. I am not sure on the UK.
    ZDD
     

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