Why the wait to fly?

[tursiops]

Dan updates their study on this every few years, based on actual research and peoples experiences. Idk what the current recommendation is off thr top of my head

No, they don't. They set their recommendations 20+ years ago based on the link I gave above, and haven't changed them since. That's DAN US. DAN Europe says 24h period, based on flawed European research.

 

[kaylee_ann]

I don't think they typically or routinely go much above 2,000 feet do they?

ah, I'm not sure. commercial ones go tens of thousands of feet high. maybe I can find info on the small resort ones somewhere
eta- small planes in general, 2-10,000 feet. I can't imagine why a resort one would go very high so you're likely right.

 

[Nick_Radov]

A NON-diver on a plane departing sea level that loses cabin pressure when reaching 30,000 ft will have a GF99 over 180%. It would be an issue for anyone.

In practice it's not an issue worth worrying about for anyone on a commercial flight regardless of whether they have been diving or not. The pilots will descend to 10000 ft or lower within a few minutes. Bubbles don't form instantly.

Ask the Captain: How fast can a plane descend if cabin pressure is lost?

This week, retired US Airways Captain John Cox discusses what is done in the event a cabin loses pressure and recalls his scariest flying experience.

www.usatoday.com

 

[stepfen]

according to their website, for one no-deco stop dive it's 12 hours. Multi-day or repetitive dives would be 18, and a decompression dive is 24 hours.

This always makes me wonder. Accelerated deco dives (even with 50% O2) quite often end with GFs quite lower than the typical multiday NDL dives.
Doesn't that matter in time before flight considerations?

One can get out of water following multiday NDL dives with GF ~70-80% or more.
Doing (conservative accelerated) deco dive(s) one can easily finish with GFs lower that 70% - even much lower than that. Isn't that "safer" ??

Or to put it in another way. Is there a reason to believe that some deco dives with a GF at the end of the last dive of say 70% are more dangerous than some NDL dives with the same end GF?

I understand that agencies can't base their guidelines in GFs. After all it is something new and hence not fully researched yet.

I am asking what you guys think.
Cheers

 

[kaylee_ann]

This always makes me wonder. Accelerated deco dives (even with 50% O2) quite often end with GFs quite lower than the typical multiday NDL dives.

If you’re doing maybe one or two deco stop dives and several NDL dives, I’d assume you’d end up on gassing more nitrogen cumulatively from NDLs. But I haven’t calculated to find out

Doesn't that matter in time before flight considerations?

One can get out of water following multiday NDL dives with GF ~70-80% or more.
Doing (conservative accelerated) deco dive(s) one can easily finish with GFs lower that 70% - even much lower than that. Isn't that "safer" ??

Or to put it in another way. Is there a reason to believe that some deco dives with a GF at the end of the last dive of say 70% are more dangerous than some NDL dives with the same end GF?

I understand that agencies can't base their guidelines in GFs. After all it is something new and hence not fully researched yet.

I am asking what you guys think.
Cheers

Ooh, interesting question. Here’s my theory:

So in NDL diving, only the GF-high value really matters because it defines basically how long your NDL is, since it controls how close you surface to the max inert gas pressure/M-value line that the “controlling tissue compartment” can have without bubbling too much. (my thoughts, not sure if it’s 100% accurate)

In decompression stop dives, the GF-low value also counts, to define your first deco stop, or the percentage of that max pressure you want to stop at. So it seems like the surfacing gradient factors from an NDL and a deco stop dive can’t fully be compared.

To answer your general question, you will always on gas more nitrogen and surface with more excess nitrogen on a deco stop dive. Sometimes you go deeper and stay longer, or just stay longer- either way, you’re taking in more N2.

An NDL dive will not saturate your tissues nearly as much because you’re not at depth long enough to match the saturation level of a deco dive.

Safer? No, I wouldn’t say that. The higher pressure of N2 still in your body makes you at higher risk for DCS at altitude change, and in general.

I’m sure someone here will correct me if I’m way off the mark.

 

[boulderjohn]

No, they don't. They set their recommendations 20+ years ago based on the link I gave above, and haven't changed them since. That's DAN US. DAN Europe says 24h period, based on flawed European research.

This is correct.

DAN Europe has called for 24 hours for a long time, and few years ago they confirmed their belief with an absolutely maddening study in which they tested divers for bubbles immediately after a dive and then 24 hours later. The divers tested 24 hours later were bubble-free, so they said that this proved that 24 hours was indeed sufficient. Yes, 24 hours was shown to be sufficient, but it does not mean it was necessary. Why they didn't test them sooner than 24 hours is a mystery.

There have been very few cases of DCS after flying, and it was a couple cases that occurred before there was any such policy that spurred things along. The problem with using any cases of DCS after flying to prove a point is that people get DCS after diving without flying, too. In many cases we don't know why they got DCS. How do we know that flying was a factor if people flew after their dives?

In one of the many threads on this topic years ago, a well-regarded participant named Lynne Flaherty (TS&M) said she had a suspicion that people who get bent after flying were already bent when they got on the plane. Of course, there is no way to prove this.

 

[boulderjohn]

24 hours before flying is now considered a bit too conservative.

Even PADI is saying:

It's been that way for a long time. That PADI policy was in effect when I was certified a quarter century ago.

 

[hammet]

Not sure if it was covered above but as a pilot, I can say that the FAA specifies in the AIM 8-1-2-d:

Decompression Sickness After Scuba Diving.

1. A pilot or passenger who intends to fly after scuba diving should allow the body sufficient time to rid itself of excess nitrogen absorbed during diving. If not, decompression sickness due to evolved gas can occur during exposure to low altitude and create a serious inflight emergency.
2. The recommended waiting time before going to flight altitudes of up to 8,000 feet is at least 12 hours after diving which has not required controlled ascent (nondecompression stop diving), and at least 24 hours after diving which has required controlled ascent (decompression stop diving). The waiting time before going to flight altitudes above 8,000 feet should be at least 24 hours after any SCUBA dive. These recommended altitudes are actual flight altitudes above mean sea level (AMSL) and not pressurized cabin altitudes. This takes into consideration the risk of decompression of the aircraft during flight.

more info:

https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/dcs.pdf

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_61-107B_CHG_1.pdf

Aircraft Pressurization

Aircraft pressurization systems provide a safe cockpit environment to sustain high altitude operations.

www.cfinotebook.net

 

[hammet]

Commercial jets do, but I'm not sure that even the small 6-8-seater planes have them. I wouldn't be surprised if the tiny transport ones at resorts don't.

It's not the pressurization per se that is required on any particular flight, it's the the partial pressure of oxygen available.

FAA requirements are :

• Sea Level to 12,500' - No oxygen required.
• 12,501' to 14,000' - Required by the required crew if over 30 minutes at this altitude.
• 14,001' to 15,000' - Required to be provided and used by the required flight crew.
• 15,001' to 25,000' - Must be provided for every occupant.

Lot's of smaller general aviation aircraft that fly higher altitudes but are not pressurized have on board or portable oxygen systems which can be used through a mask or cannula (tube going into your nose like in a hospital). Hypoxia (lack of oxygen) symptoms can occur at lower altitudes than mentioned above depending on conditions (fatigue, alcohol, etc). Many pilots choose to not fly over 5000' at night as hypoxia can affect night vision. Flying at higher altitudes, general aviation pilots often use a pulse oximeter on their fingers to monitor the O2 saturation of their blood.

Most smaller piston engine planes will not have pressurization. Turbojet and turboprop engines are able to bleed compressed air from the engines into the cabin and therefore typically have pressurized cabins. There aren't too many planes that carry more than 6 people (incl crew) that aren't turboprops with pressurized cabins.

 

[MtnDiverColorado]

See https://scubaboard.com/community/resources/flying-after-diving-dan-workshop-report-2002.19/ if you want all the details.

Thanks to everyone whose replied. I thought this report really interesting, particularly the below. 3 out of 36 people with a 3 hour surface interval ended up bent. yikes....