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Masks : Function of nose-pockets ?

Discussion in 'Fins, Masks and Snorkels' started by Fishy, Mar 18, 2002.

  1. Fishy

    Fishy Garibaldi

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    Picky question from a recent SSI Basic Scuba graduate ...

    In the multiple-choice section of the course, one of the questions was "why does the mask have a nose-pocket?"

    The official answer was to allow equalisation whilst descending (as stated in the manual), whereas I put 'to avoid mask squeeze'. Surely one can equalise the ears/sinuses without a nose-pocket by holding nose/blowing in the usual way - since the nose is sealed by the fingers, what use is the nose-pocket ?

    However, the nose-pocket is the only means of introducing air into the mask in a mask squeeze situation, so exhaling into the mask via nose is the only way of avoiding mask squeeze.

    Any support out there ? There could be a few beers riding on this one ...
     
  2. Scubaroo

    Scubaroo Great White

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    Two reasons:

    1. Mask squeeze - adding more air to the mask reduces the pressure differential between the air inside the mask and the surrounding water, reducing discomfort caused by a partial vacuum effect pulling the mask against your face

    2. Mask clearing - if your mask floods, exhaling through your nasal passages allows displacement of the water from the mask

    Say it exactly like that and he'll think you looked it up in a book somewhere and must be right :)

    Also unofficial reason #3 - catch all the boogers during the dive
     
  3. neil

    neil Dive Charter

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    That's correct: to equalize the air space in the mask, thereby avoiding mask squeeze. The squeeze in your mask is the same process as the squeeze in your ears: less pressure outside than inside. You "equalize" by adding pressure inside to match pressure outside, whether it's a mask or ears. I'm not sure who gets to buy the beer :)

    Neil
     
  4. neil

    neil Dive Charter

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    OF COURSE, I meant less pressure inside than outside. Too many Guinesses tonight. DUH.

    Neil
     
  5. Walter

    Walter Instructor, Scuba

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    In the days of yore masks didn't have nose pockets, but they still covered the nose. It is easy to equalize the pressure in your mask with or without a nose pocket as long as the mask covers your nose. For most divers it is not as easy (although it is still possible) to equalize the pressure in their ears without a nose pocket.

    Sorry, but your instructor is totally correct on this one. You misread the question thinking it meant why must the mask cover the nose. That was not what the question asked. It was asking why the mask is shaped in a particular way in the area that covers the nose.

    Buy the beer.
     
  6. roakey

    roakey Old, not bold diver ScubaBoard Supporter

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    Location: Colorado Springs, CO
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    Another reason for a nose pocket is to move the glass closer to the eyes to give you better peripheral vision.

    Does anyone remember the old joke about the test question “Using a barometer, how would you measure the height of a building?” :)

    Roak
     
  7. Ontario Diver

    Ontario Diver Loggerhead Turtle

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    Since the nose sticks out the most on a face, having a nose pocket allows the mask to have a lower volume - leading to easier equalization.
     
  8. TexasMike

    TexasMike Loggerhead Turtle

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    For me, it also serves as a reminder not to inhale through my nose. Since doing so introduces a slight mask squeeze.
     
  9. The Chairman

    The Chairman Chairman of the Board

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    Why it's important to have a mask with the lens still intact. I think he figured this one out fairly recently... :tease:
     
  10. jbd

    jbd Dive Shop

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    Any illuminating thoughts on Pete's post above?

    Roakey-never heard that one. Will you enlightment me?
     

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