+ Reply to Thread
Results 1 to 10 of 10

Thread: Quantifying WOB?

  1. #1
    All IMVHO obviously... Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field's Avatar
    Join Date
    Aug 2005
    Location
    Weymouth, England
    Posts
    3,023
    NVMCCR Inspiration

    Classic KISS, Sport KISS

    Quantifying WOB?

    Hi All,

    Following a Pub discussion in which someone ideally mentioned WOB as being "better" on one unit over another we got talking about how WOB is quantified.

    Obviously Joule/litre is a figure often quoted but what does it mean in the real world?

    Is 3J/L 2% more than 1 or 2/3rds greater? etc... What is the WOB (in J/L) of sucking Milkshake up a McDonalds straw or air down a snorkle?

    For that matter what is a WOB of normal breathing sitting in front of this screen?

    I understand WOB is important but I get the impression that some people are swearing by figures they have no idea how they relate to the real world

    We know running is faster than walking because we understand Miles per Hour, I'm sure most of us don't understand Joules per Litre... I know what Joules per Litre means but I don't know what other breathing related activities are in Joules per litre to quantify it?

    BEN

  2. #2
    Banned Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn has much to be proud of Brad_Horn's Avatar
    Join Date
    Mar 2005
    Location
    Canberra
    Posts
    1,076
    Apoc

    Drager

    Re: Quantifying WOB?

    Ben,

    This doesn't answer your question, but you may find it of interest.

    The Lung at Depth - Google Book Search

    'The Lung at Depth, pages 31/32 has an abstract on WOB.

    There was also some discussion on what WOB is IIRC in the DAN 2008 Tech Conference .mp4s/DVD (Clarke & Anthony at least) that may expand on why the current WOB limits are as they are.

    Regards
    Brad
    Last edited by Brad_Horn; 4th September 2008 at 14:38.

  3. #3
    Nicholas Smith Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo has a reputation beyond repute Abbo's Avatar
    Join Date
    Aug 2006
    Location
    Tokyo
    Posts
    673
    Megalodon

    Re: Quantifying WOB?

    Quote Originally Posted by Ben Field  View Original Post
    What is the WOB (in J/L) of sucking Milkshake up a McDonalds straw or air down a snorkle?
    Obviously the Earth's gravitational field strength is 9.8 Newtons per kilogram, so 100g laid on my hand would have a force of 1N. A joule is the work done by moving a newton through a metre. So 2 joules/ litre means that a 5 litre tidal volume (pretty normal breath) requires the work of moving a kilogramme through a metre. That really doesn't sound very much. Most rebreathers are a bit over 2 J/l.

    The trouble, of course, is that WOB does not have to be very high before it results in CO2 buildup and all the nasty things that go with that. That's the bit that I don't follow: why does the CO2 build up, and how, at such low levels of work?

  4. #4
    RBW Member nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh has much to be proud of nigelh's Avatar
    Join Date
    Mar 2005
    Posts
    1,382

    Re: Quantifying WOB?

    One thing that I always wondered about WoB was seeing some divers that had replaced their Inspo harnesses with a backplate and used bungie rather than a fixed length strap to attach the counterlungs to the waist.
    While this looked admirable in keeping the C/Ls snug against the chest I did feel it was like something carefully set to stretch on every breath and contribute to WoB not on the gas side but on the outside.

    Now, knowing rather a lot about gas flow but not much about the medicine involved, I wondered if this was relevant. Is the problem with WoB to do with the physical work expended in the chest muscles causing you to shallow breathe? I can't see it involving differential pressures due to restrictions because the flow rates are too slow and residuals would settle out very quickly (fractions of a second).

    Can anybody put me right on this one?

  5. #5
    Choose Freedom - UKIP Scubascooby is a jewel in the rough Scubascooby is a jewel in the rough Scubascooby is a jewel in the rough Scubascooby is a jewel in the rough Scubascooby is a jewel in the rough Scubascooby is a jewel in the rough Scubascooby is a jewel in the rough Scubascooby's Avatar
    Join Date
    Nov 2005
    Location
    Great Britain
    Posts
    678

    Re: Quantifying WOB?

    I think what Ben is getting at is, how does the body respond to different WoB. Is it linear (I doubt it) or is there a tipping point or something else ?

    If Unit X has WoB of 3 J/L and Unit Y has 3.1J/L does it matter or has some vital point been passed ?

    I wonder what the variation is between two units off the production line ?

    Joule was a clever bloke from Salford whose father owned a brewery. Joule was taught by Dalton.

  6. #6
    All IMVHO obviously... Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field has a reputation beyond repute Ben Field's Avatar
    Join Date
    Aug 2005
    Location
    Weymouth, England
    Posts
    3,023
    NVMCCR Inspiration

    Classic KISS, Sport KISS

    Re: Quantifying WOB?

    Thanks guys... all kind-of what I was driving at.

    I know what a joule is and all but my point was how does it "relate" to us and saying if something breaths good/bad when we know the WOB. I see where Abbo is coming from but obviously the actual WOB meansurements are there for the the purpose of getting under certain limits, and I can see why there are limits but how do they compare in the grand scheme?

    For example-
    Walking 2mph, Running 10mph, Driving 65mph, Flying 400mph

    The fastest I can go on my own is 10mph but I can drive at 65 so its worth having a car, I don't have a plane or space to put one therefore its of no use to me- I can make a choise based on a list of data...

    Similar WOB chart-
    Sitting at desk- ?
    Snorkeling- ?
    OC Reg- ?
    RB DSV- ?
    RB BOV- ?
    Different BOV- ?
    Sucking Pea soup up a Straw-?

    Some people are stating things like- "Rebreather X has lower WOB than Y, I would therefore reccomend X"

    Is that a fair statment, are the WOB figures relavent enough to the real world? Where on the grand scale of things do they sit?

  7. #7
    Cave Addict CCR Josh is on a distinguished road CCR Josh is on a distinguished road CCR Josh's Avatar
    Join Date
    Aug 2008
    Location
    Utah / Florida :)
    Posts
    412
    HammerHead

    Sentinel-Inspo-Optima-Prism 2

    Re: Quantifying WOB?

    I would also be curious as to the comparison to "normal daily activities".....


    I am new to the CCR world so correct me if I am wrong:

    More volume (ie. higher RMV) = higher WoB

    More density (ie. Deeper) = higher WoB

    Higher WoB = higher CO2 production


    So.... wouldn't ANY difference in WoB between different rebreathers / configs be a matter of great importance?

  8. #8
    Explorers Exodus Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing has a brilliant future Hanssing's Avatar
    Join Date
    Nov 2005
    Location
    Denmark
    Posts
    912
    rEvo-II

    Re: Quantifying WOB?

    AD_Ward9 has published extensively on this.

    The WOB is derived froma lisa-joule chart, and they way its derived is enough that is can be physically meaningless.

    I'll try and see if I can dig up some of ADs post and reference them in here later. For now let me presnet my own halfassed ramblings:

    The WOB is then defined as the area in the curve, but this area wich pr. definition is the WOB does not translate to a good *percieved* WOB.
    You could have a constant negative pressure at the mouthpiece, and a lissajou-curve with very low area, allways operationg with the negative pressure. This woudl mean that the WOB is low, but your breathing from a vaccum-cleaner!

    So AFAIK the current standards do not define GOOD wob, as they dont factor in the absolute-pressure, in essence this would mean that a snorkle with a large bore at depth of 1msw woudl have execellent WOB, but have an terrible *percieved* WOB.

    AD (yeah I'm his groupie) did suggest that the absolute values be used for WOB-meassurements, this would then not translate to the pysical work the diver perofrms on his surroundings, but to a WOB-value wich is MUCH more related to a good WOB. The snorkel-example would then have an extremely high WOB. If this is adopted then in order to have a good WOB the area has to be centered around the 0mbar line, wich would translate as good percieved WOB.

    All in all its not that simple to classify WOB as good or bad. We have a nummerical meassuremnt, but in its current form its correct, but not physically meaningfull.

    I'm off to find the posts:

    Got it: Somewhere aound this one: http://www.rebreatherworld.com/showthread.php?t=14619
    Otherwise do a search for lissajou and enjoy.

    Nicolai
    Last edited by Hanssing; 4th September 2008 at 17:05.

  9. #9
    Reads fine print (mostly) Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather has a brilliant future Skipbreather's Avatar
    Join Date
    Mar 2005
    Location
    Chicago, Illinois, USA
    Posts
    1,331
    MEGALODON MK15.5

    BMR500 IDA71 IDA64 RGUFM AKA60

    Re: Quantifying WOB?

    Quote Originally Posted by Ben Field  View Original Post
    T I can make a choise based on a list of data...

    Similar WOB chart-
    Sitting at desk- ?
    Snorkeling- ?
    OC Reg- ?
    Rebreather DSV- ?
    Rebreather BOV- ?
    Different BOV- ?
    Sucking Pea soup up a Straw-?
    Suck starting a Harley Davidson...............? :p

  10. #10
    Unbanned cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn has a reputation beyond repute cramerdn's Avatar
    Join Date
    Dec 2006
    Location
    Middle TN
    Posts
    1,715

    Re: Quantifying WOB?

    Quote Originally Posted by Skipbreather  View Original Post
    Suck starting a Harley Davidson...............? :p
    Don't they suck enough by themselves


    I assumed J/l was a measure of the resistance to flow. If a liter of gas moves then some number of joules are used to move it based on its mass and acceleration applied to it. I assumed the WOB is the J/l extra that's needed above what should have been required.

+ Reply to Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts