Use of FFM risk with sealed attached hoods on deep cold water dives

Drmike · 3rd October 2007, 06:05

Cold water diving using air or argon for suit inflation.

I was pondering over the use of a full face mask sealed against outside of an attached hood on deep mix dives (200m) long explosures (6+hrs) high HE content in mix diving on a rebreather.

6 deg C water (47 Deg F) 6 +hr explosures hence wish to use FFM and attached hood with face seal.

Im wondering, on ascent the neck seal vents into the sealed hood which in turn may, given the above, vent into the FFM (if the FFM is sealing agaisnt the hood outer seal)

If this was to happen you could have your face and nose and ears/eyes seeing a different gas to what your breathing...any issues with that???

Any nose breathing could result in breathing these wrong gases
How do cold water FFM divers deal with this issue? I can imagine being at 600ft and the neck seal burps 79% N2 into your FFM and you beathe that in via the nose, it could be a bit nasty given the small volume of the mask you effectively would be taking a lung full of air with EAD of 200m

Or, do you put vent holes in the attached hood top to vent excess gas that way?

If so wouldnt those vent holes defeat the object of the face seal and attached hood in the 1st place? (no longer dryish head) would they prevent any gas sepage?

Another qustion is with a attached hood sealed with a FFM how easiy will it be to equalise the hood on descent?? The face hood seal would be tight against the face so nose venting wouldnt help - you would have to get gas to burb through the kneck seal........? or again do you put holes in the hood near the ears?

I guess an attached hood can still be used without sealing the face mask to it, instead sealing it to the face. That would remove the risk of venting into the FFM and make equalising easier (now a wet'ish hood)

maybe that the best way.

When I see pics of people diving v cold water with ffm they apear to have them sealed agaisnt their attached hoods.........??

Given all the above do I take it that attached hood with face seals and with FFM sealed to these face seals arent actually 'dry' utilising small vent holes in the hood, and the seals only used to help prevent water circulation to effect benefit of warmer dives?

jhaaja · 3rd October 2007, 06:26

Quote: (Originally Posted by Drmike)

Cold water diving using air or argon for suit inflation.

I was pondering over the use of a full face mask sealed against outside of an attached hood on deep mix dives (200m) long explosures (6+hrs) high HE content in mix diving on a rebreather.

6 deg C water (47 Deg F) 6 +hr explosures hence wish to use FFM and attached hood with face seal.

Im wondering, on ascent the neck seal vents into the sealed hood which in turn may, given the above, vent into the FFM (if the FFM is sealing agaisnt the hood outer seal)

If this was to happen you could have your face and nose and ears/eyes seeing a different gas to what your breathing...any issues with that???

Any nose breathing could result in breathing these wrong gases
How do cold water FFM divers deal with this issue? I can imagine being at 600ft and the neck seal burps 79% N2 into your FFM and you beathe that in via the nose, it could be a bit nasty given the small volume of the mask you effectively would be taking a lung full of air with EAD of 200m

Or, do you put vent holes in the attached hood top to vent excess gas that way?

If so wouldnt those vent holes defeat the object of the face seal and attached hood in the 1st place? (no longer dryish head) would they prevent any gas sepage?

Another qustion is with a attached hood sealed with a FFM how easiy will it be to equalise the hood on descent?? The face hood seal would be tight against the face so nose venting wouldnt help - you would have to get gas to burb through the kneck seal........? or again do you put holes in the hood near the ears?

I guess an attached hood can still be used without sealing the face mask to it, instead sealing it to the face. That would remove the risk of venting into the FFM and make equalising easier (now a wet'ish hood)

maybe that the best way.

When I see pics of people diving v cold water with ffm they apear to have them sealed agaisnt their attached hoods.........??

Given all the above do I take it that attached hood with face seals and with FFM sealed to these face seals arent actually 'dry' utilising small vent holes in the hood, and the seals only used to help prevent water circulation to effect benefit of warmer dives?

I think you must use a mask that prevents the gas inside the mask entering your lungs. Like Interspiro mask that has a inner sealed "cup" that just surrounds your mouth and nose. This way the gas inside the mask in general can not be breathed.

About the equalising I see no problem. I use a tight dry hood (made of latex rubber not neopren) and I have no difficulties in equalising it from my half mask. I also have a neck seal on that suit. The neck seal is not necessary but I like to have it. It makes it easier to keep some gas in the hood. In caves I have to go down head firtst and without the neck seal all the gas in the hood escapes to the suit. This makes a nasty feeling in the ears.

JH
Finland, land of cold water

Drmike · 3rd October 2007, 06:37

Quote: (Originally Posted by jhaaja)

I think you must use a mask that prevents the gas inside the mask entering your lungs. Like Interspiro mask that has a inner sealed "cup" that just surrounds your mouth and nose. This way the gas inside the mask in general can not be breathed.

About the equalising I see no problem. I use a tight dry hood (made of latex rubber not neopren) and I have no difficulties in equalising it from my half mask. I also have a neck seal on that suit. The neck seal is not necessary but I like to have it. It makes it easier to keep some gas in the hood. In caves I have to go down head firtst and without the neck seal all the gas in the hood escapes to the suit. This makes a nasty feeling in the ears.

JH
Finland, land of cold water

Thanks for that feedback,

So you can equalize your hood by equalizing your mask? The gas passing under and into latex hood from your mask. Great that's one less thing to worry about.

Makes sense re: the oral-nasal cup. My FFM has a mouthbite so nose is open. I guess I could fit a nose clip - but I do find them very uncomfortable
after a short time.

Another option maybe to leave the nose equalising paddles in the down position. They don't apply any force but at least they may close the nose a little to add resistance to any accidental breathing with the benefit I can open then if they start to annoy or if i wish to nose breathe

With a nose clip I can still spit out the mouthbite and 'mouth' breathe off the side reg if I still need to get some sanity breaths so that's still doable.

I presume with your latex hood when ascending any gas vents out of your half mask??

Cheers
Mike

jhaaja · 3rd October 2007, 06:47

Quote: (Originally Posted by Drmike)

Thanks for that feedback,

So you can equalize your hood by equalizing your mask? The gas passing under and into latex hood from your mask. Great that's one less thing to worry about.

Makes sense re: the oral-nasal cup. My FFM has a mouthbite so nose is open. I guess I could fit a nose clip - but I do find them very uncomfortable
after a short time.

Another option maybe to leave the nose equalising paddles in the down position. They don't apply any force but at least they may close the nose a little to add resistance to any accidental breathing with the benefit I can open then if they start to annoy or if i wish to nose breathe

With a nose clip I can still spit out the mouthbite and 'mouth' breathe off the side reg if I still need to get some sanity breaths so that's still doable.

I presume with your latex hood when ascending any gas vents out of your half mask??

Cheers
Mike

The latex hood is not flexible so it does not really collect any gas in it. Some gas usually still leaks through the neck seal and the hood on ascent but the amount is small. The hood is nice compared to neopren wet hoods. It is warmer and you don´t get that "Alien Swollen Head" on accent

JH

Drmike · 3rd October 2007, 07:10

Quote: (Originally Posted by jhaaja)

The latex hood is not flexible so it does not really collect any gas in it. Some gas usually still leaks through the neck seal and the hood on ascent but the amount is small. The hood is nice compared to neopren wet hoods. It is warmer and you don´t get that "Alien Swollen Head" on accent

JH

Thanks,

Any disadvantage of using a latex dryhood?

jhaaja · 3rd October 2007, 07:12

Quote: (Originally Posted by Drmike)

Thanks,

Any disadvantage of using a latex dryhood?

Funny looking head

The hood has to be custom made to your head for a good fit. It is a bit hard to sell your suit. But why sell it.

I really like my hoods and I have the same type of hood on both of my suits.

JH

Ben Field · 3rd October 2007, 07:17

Quote: (Originally Posted by Drmike)

Or, do you put vent holes in the attached hood top to vent excess gas that way?

If so wouldnt those vent holes defeat the object of the face seal and attached hood in the 1st place? (no longer dryish head) would they prevent any gas sepage?

Not sure how relavent this is as I don't dive FFM but- I have an O'three neoprene hood, it has a double layer of thinner neoprene along the "spine" running from forehead to nape of neck, the inner layer has small holes and the outer layer has small holes alternately placed. These act like a one way valve, air gets out but little or no water comes back in. No alien/egg head impressions here!

Drmike · 3rd October 2007, 07:21

Quote: (Originally Posted by jhaaja)

Funny looking head

can only be an improvement

Drmike · 3rd October 2007, 07:25

Quote: (Originally Posted by Ben Field)

Not sure how relavent this is as I don't dive FFM but- I have an O'three neoprene hood, it has a double layer of thinner neoprene along the "spine" running from forehead to nape of neck, the inner layer has small holes and the outer layer has small holes alternately placed. These act like a one way valve, air gets out but little or no water comes back in. No alien/egg head impressions here!

thanks,

yeh Ive seen one of those. I was thinking it might be possible to fit an exhaust valve on top of the hood ...sounds daft but might work

I guess though If the kneck seal is tight enough and retaining horizontal trim I guess little gas will get into the hood anyway plus with all that deco time and slow ascents achieving almost all suit venting through the shoulder dump shouldnt be an issue.

cheers
mike

jhaaja · 3rd October 2007, 07:32

I have seen some people cut small holes in the back of the hood to aid gas getting out. You can allways start squeezing yor swollen head to get the gas out

Me likes LATEX

(blacK

JH

3rd October 2007, 06:05	#1 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,323	Use of FFM risk with sealed attached hoods on deep cold water dives Cold water diving using air or argon for suit inflation. I was pondering over the use of a full face mask sealed against outside of an attached hood on deep mix dives (200m) long explosures (6+hrs) high HE content in mix diving on a rebreather. 6 deg C water (47 Deg F) 6 +hr explosures hence wish to use FFM and attached hood with face seal. Im wondering, on ascent the neck seal vents into the sealed hood which in turn may, given the above, vent into the FFM (if the FFM is sealing agaisnt the hood outer seal) If this was to happen you could have your face and nose and ears/eyes seeing a different gas to what your breathing...any issues with that??? Any nose breathing could result in breathing these wrong gases How do cold water FFM divers deal with this issue? I can imagine being at 600ft and the neck seal burps 79% N2 into your FFM and you beathe that in via the nose, it could be a bit nasty given the small volume of the mask you effectively would be taking a lung full of air with EAD of 200m Or, do you put vent holes in the attached hood top to vent excess gas that way? If so wouldnt those vent holes defeat the object of the face seal and attached hood in the 1st place? (no longer dryish head) would they prevent any gas sepage? Another qustion is with a attached hood sealed with a FFM how easiy will it be to equalise the hood on descent?? The face hood seal would be tight against the face so nose venting wouldnt help - you would have to get gas to burb through the kneck seal........? or again do you put holes in the hood near the ears? I guess an attached hood can still be used without sealing the face mask to it, instead sealing it to the face. That would remove the risk of venting into the FFM and make equalising easier (now a wet'ish hood) maybe that the best way. When I see pics of people diving v cold water with ffm they apear to have them sealed agaisnt their attached hoods.........?? Given all the above do I take it that attached hood with face seals and with FFM sealed to these face seals arent actually 'dry' utilising small vent holes in the hood, and the seals only used to help prevent water circulation to effect benefit of warmer dives? __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment
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3rd October 2007, 06:26	#2 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: Use of FFM risk with sealed attached hoods on deep cold water dives Quote: (Originally Posted by Drmike) Cold water diving using air or argon for suit inflation. I was pondering over the use of a full face mask sealed against outside of an attached hood on deep mix dives (200m) long explosures (6+hrs) high HE content in mix diving on a rebreather. 6 deg C water (47 Deg F) 6 +hr explosures hence wish to use FFM and attached hood with face seal. Im wondering, on ascent the neck seal vents into the sealed hood which in turn may, given the above, vent into the FFM (if the FFM is sealing agaisnt the hood outer seal) If this was to happen you could have your face and nose and ears/eyes seeing a different gas to what your breathing...any issues with that??? Any nose breathing could result in breathing these wrong gases How do cold water FFM divers deal with this issue? I can imagine being at 600ft and the neck seal burps 79% N2 into your FFM and you beathe that in via the nose, it could be a bit nasty given the small volume of the mask you effectively would be taking a lung full of air with EAD of 200m Or, do you put vent holes in the attached hood top to vent excess gas that way? If so wouldnt those vent holes defeat the object of the face seal and attached hood in the 1st place? (no longer dryish head) would they prevent any gas sepage? Another qustion is with a attached hood sealed with a FFM how easiy will it be to equalise the hood on descent?? The face hood seal would be tight against the face so nose venting wouldnt help - you would have to get gas to burb through the kneck seal........? or again do you put holes in the hood near the ears? I guess an attached hood can still be used without sealing the face mask to it, instead sealing it to the face. That would remove the risk of venting into the FFM and make equalising easier (now a wet'ish hood) maybe that the best way. When I see pics of people diving v cold water with ffm they apear to have them sealed agaisnt their attached hoods.........?? Given all the above do I take it that attached hood with face seals and with FFM sealed to these face seals arent actually 'dry' utilising small vent holes in the hood, and the seals only used to help prevent water circulation to effect benefit of warmer dives? I think you must use a mask that prevents the gas inside the mask entering your lungs. Like Interspiro mask that has a inner sealed "cup" that just surrounds your mouth and nose. This way the gas inside the mask in general can not be breathed. About the equalising I see no problem. I use a tight dry hood (made of latex rubber not neopren) and I have no difficulties in equalising it from my half mask. I also have a neck seal on that suit. The neck seal is not necessary but I like to have it. It makes it easier to keep some gas in the hood. In caves I have to go down head firtst and without the neck seal all the gas in the hood escapes to the suit. This makes a nasty feeling in the ears. JH Finland, land of cold water
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3rd October 2007, 06:37	#3 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,323	Re: Use of FFM risk with sealed attached hoods on deep cold water dives Quote: (Originally Posted by jhaaja) I think you must use a mask that prevents the gas inside the mask entering your lungs. Like Interspiro mask that has a inner sealed "cup" that just surrounds your mouth and nose. This way the gas inside the mask in general can not be breathed. About the equalising I see no problem. I use a tight dry hood (made of latex rubber not neopren) and I have no difficulties in equalising it from my half mask. I also have a neck seal on that suit. The neck seal is not necessary but I like to have it. It makes it easier to keep some gas in the hood. In caves I have to go down head firtst and without the neck seal all the gas in the hood escapes to the suit. This makes a nasty feeling in the ears. JH Finland, land of cold water Thanks for that feedback, So you can equalize your hood by equalizing your mask? The gas passing under and into latex hood from your mask. Great that's one less thing to worry about. Makes sense re: the oral-nasal cup. My FFM has a mouthbite so nose is open. I guess I could fit a nose clip - but I do find them very uncomfortable after a short time. Another option maybe to leave the nose equalising paddles in the down position. They don't apply any force but at least they may close the nose a little to add resistance to any accidental breathing with the benefit I can open then if they start to annoy or if i wish to nose breathe With a nose clip I can still spit out the mouthbite and 'mouth' breathe off the side reg if I still need to get some sanity breaths so that's still doable. I presume with your latex hood when ascending any gas vents out of your half mask?? Cheers Mike __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by Drmike : 3rd October 2007 at 06:45.
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3rd October 2007, 06:47	#4 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: Use of FFM risk with sealed attached hoods on deep cold water dives Quote: (Originally Posted by Drmike) Thanks for that feedback, So you can equalize your hood by equalizing your mask? The gas passing under and into latex hood from your mask. Great that's one less thing to worry about. Makes sense re: the oral-nasal cup. My FFM has a mouthbite so nose is open. I guess I could fit a nose clip - but I do find them very uncomfortable after a short time. Another option maybe to leave the nose equalising paddles in the down position. They don't apply any force but at least they may close the nose a little to add resistance to any accidental breathing with the benefit I can open then if they start to annoy or if i wish to nose breathe With a nose clip I can still spit out the mouthbite and 'mouth' breathe off the side reg if I still need to get some sanity breaths so that's still doable. I presume with your latex hood when ascending any gas vents out of your half mask?? Cheers Mike The latex hood is not flexible so it does not really collect any gas in it. Some gas usually still leaks through the neck seal and the hood on ascent but the amount is small. The hood is nice compared to neopren wet hoods. It is warmer and you don´t get that "Alien Swollen Head" on accent JH
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3rd October 2007, 07:10	#5 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,323	Re: Use of FFM risk with sealed attached hoods on deep cold water dives Quote: (Originally Posted by jhaaja) The latex hood is not flexible so it does not really collect any gas in it. Some gas usually still leaks through the neck seal and the hood on ascent but the amount is small. The hood is nice compared to neopren wet hoods. It is warmer and you don´t get that "Alien Swollen Head" on accent JH Thanks, Any disadvantage of using a latex dryhood? __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment
(Offline)

3rd October 2007, 07:12	#6 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: Use of FFM risk with sealed attached hoods on deep cold water dives Quote: (Originally Posted by Drmike) Thanks, Any disadvantage of using a latex dryhood? Funny looking head The hood has to be custom made to your head for a good fit. It is a bit hard to sell your suit. But why sell it. I really like my hoods and I have the same type of hood on both of my suits. JH
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3rd October 2007, 07:17	#7 (permalink)
Ben Field CK+Shearwater Current Rebreather/s: Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2005 Location: London, England Posts: 1,621	Re: Use of FFM risk with sealed attached hoods on deep cold water dives Quote: (Originally Posted by Drmike) Or, do you put vent holes in the attached hood top to vent excess gas that way? If so wouldnt those vent holes defeat the object of the face seal and attached hood in the 1st place? (no longer dryish head) would they prevent any gas sepage? Not sure how relavent this is as I don't dive FFM but- I have an O'three neoprene hood, it has a double layer of thinner neoprene along the "spine" running from forehead to nape of neck, the inner layer has small holes and the outer layer has small holes alternately placed. These act like a one way valve, air gets out but little or no water comes back in. No alien/egg head impressions here! __________________ Know your PPO2, Pre-breath, Use checklists, Validate cells at 6mtrs, Use pure O2 at or near surface, Use a BOV, Don't dive Solo, Change Slime and Cells as recommended by Manufacturer and RTFM! Beware Fridge Suck! www.hugsac.org.uk
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3rd October 2007, 07:25	#9 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,323	Re: Use of FFM risk with sealed attached hoods on deep cold water dives Quote: (Originally Posted by Ben Field) Not sure how relavent this is as I don't dive FFM but- I have an O'three neoprene hood, it has a double layer of thinner neoprene along the "spine" running from forehead to nape of neck, the inner layer has small holes and the outer layer has small holes alternately placed. These act like a one way valve, air gets out but little or no water comes back in. No alien/egg head impressions here! thanks, yeh Ive seen one of those. I was thinking it might be possible to fit an exhaust valve on top of the hood ...sounds daft but might work I guess though If the kneck seal is tight enough and retaining horizontal trim I guess little gas will get into the hood anyway plus with all that deco time and slow ascents achieving almost all suit venting through the shoulder dump shouldnt be an issue. cheers mike __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment
(Offline)

3rd October 2007, 07:32	#10 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 884	Re: Use of FFM risk with sealed attached hoods on deep cold water dives I have seen some people cut small holes in the back of the hood to aid gas getting out. You can allways start squeezing yor swollen head to get the gas out Me likes LATEX (blacK JH
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