Wikipedia:Reference desk/Archives/Science/2018 July 8

= July 8 =

Full face diving mask Vs mouth piece
Thinking about the Thai cave rescue I wondered which would use air quickest a full face mask or a mouthpiece. On one hand a full face mask would need air flow through all the time. On the other hand a mouthpiece means that air breathed out is used up even if there could be enough oxygen to breathe it again mixed with some fresh air. Intuitively I think you should be able to tune the flow of a full face mask to use air more slowly, though that might seem stale to the diver. -- Q Chris (talk) 16:27, 8 July 2018 (UTC)
 * Pure speculation but they may be using rebreathers since they have to stay underwater for a long time and supplying cylinders is difficult. This would mean they use up a large percentage of the oxygen in the cylinders. I found breathing in through my mouth rather than my nose difficult. Dmcq (talk) 17:07, 8 July 2018 (UTC)
 * (ec) Take a look at full face diving mask. Both mouthpieces and full face masks usually have on-demand air supply, i.e. you "suck" the air through a valve (more precisely, the equaliser valve opens when it detects underpressure). Both will normally also release the overpressure when you breathe out. You cannot create an over- or underpressure that would allow you to "store" air that you breathe out in the mask - neither would your lungs stand it, nor would the seal of the mask hold it. Low oxygen content is not a problem, as the partial pressure even of quite oxygen-depleted air under pressure is high. This allows experienced divers to reduce their rate of breathing to below normal - they still get plenty of oxygen, but you need to train the body to notice that. If you want maximum endurance, you can use a rebreather. These are available for full-face masks and for more normal mouth pieces. --Stephan Schulz (talk) 17:17, 8 July 2018 (UTC)
 * I suspect the issue might be that a conventional mouthpiece has to be held between the teeth - not fail-safe for an untrained kid liable to panic. "Wearing full-face masks, which are easier for novice divers than traditional respirators..." BBC News - Thailand cave rescue: Mission to save boys under wayAlansplodge (talk) 19:28, 8 July 2018 (UTC)
 * Officials Call for Donations of Small Diving Masks to Rescue Cave Boys
 * Full face diving mask
 * Amazon: Divers Full Face Mask
 * --Guy Macon (talk) 22:27, 8 July 2018 (UTC)
 * For what it's worth, PADI (one of the world's largest recreational SCUBA diving organizations) treats a full face mask as a specialized skill that requires extra training beyond the basic open-water SCUBA certificate. Rebreather Diver is a formal certificate, and before PADI will grant it, the diver must satisfy experience minima and obtain the enriched air training and certificate, also known as breathing NITROX.  Other dive agencies have similar requirements.
 * Breathing an atmosphere other-than-air can feel very strange; it requires skill and discipline to avoid physiological harm; in the case of an emergency rescue, the rescue divers would have to weigh any benefits against these serious extra workloads and risks.
 * Of course, diving in a cavern (or any other confined space) is an extremely advanced skill; and it can be extremely dangerous even in recreational settings. This rescue operation certainly falls under extraordinary circumstances; no dive instructor would want to put novice divers into such conditions if it could be avoided.  As in any emergency, standard rules and procedures take a backseat to making a safe and rapid egress.
 * Nimur (talk) 01:54, 9 July 2018 (UTC)
 * I did notice that the PADI training has a lot about setting up the mask properly (which someone experienced would do in this case), that there would be opportunity to take the children down in short test dives to see if they have any problems, and that they wouldn't have to swim but rather be dragged along. They might even administer a sedative. And of course there is no alternative. Clearly it worked with four kids so far. I wonder if they started with the sickest or with the most healthy (to work out any bugs in the system)? --Guy Macon (talk) 05:59, 9 July 2018 (UTC)
 * Media reports suggest the initial plan was possibly to bring out the strongest, but after an assessment by a doctor the decision was made to bring the weakest out first [//www.bbc.com/news/world-asia-44757804] [//www.news.com.au/world/asia/rescue-of-boys-in-tham-luang-caves-begin-as-weakest-boys-reportedly-leave-first/news-story/cfda01488f97b87ab8daad9f27c9c399] [//www.thestar.com.my/news/regional/2018/07/09/four-rescued-from-flooded-thai-cave-boys-taken-to-hospital-as-divers-keep-working-to-save-those-stil/]. According to those reports, this may have been in part, other than greater urgency for them to leave, also because it was expected that the conditions could be the best they would ever have. Nil Einne (talk) 08:50, 9 July 2018 (UTC)