Deco dive with divers on different back gas

[rjack321]

Most ridiculous comment of the day. I use air for deco dives at 100 feet or deeper.

This was originally posted in DIR and has since moved. Carry on

 

[crofrog]

That’s 18/45 on a rebreather? It’s a phenomenal waste of good helium for open circuit; 45m/150ft is a 25/25 dive on OC, or just use 25% and put up with the narcosis.

25/25 is 5.72 g/L at 150 and nx25 is 7.21g/L.

If you all want to ignore what we know how about gas density now go for it.

 

[Wibble]

45m/150ft is 5.5ata
25% is 0.25
PPO2 = P x Mix = 5.5 x 0.25 = 1.375 PPO2.

OC planning is for the bottom phase to be below 1.4 and the decompression phase below 1.6. Safe to breathe.

 

[rjack321]

45m/150ft is 5.5ata
25% is 0.25
PPO2 = P x Mix = 5.5 x 0.25 = 1.375 PPO2.

OC planning is for the bottom phase to be below 1.4 and the decompression phase below 1.6. Safe to breathe.

Except when it isn't... This woman never exceeded 1.4 and clearly toxed at 145ft on 24/25.

2007-07-14 Incident – IUCRR

iucrr.org

There is a very good reason many folks dive with 1.2 on the bottom or even less.

 

[Centrals]

Well if you end the dive with more than 30 bar in your tank then you had enough.

No you don't on tec dive. I am pretty sure you do not know how to calculate the gas requirement for tec dive.
What do you know about tec dive?

 

[Centrals]

I had done few hundred baby decompression dives but everyone in the team was breathing the same bottom and deco gases. It made life a bit easier in case of emergency.

 

[TheCatFish]

I fully agree with the recommendations but there may be situations where there is some harm. If the divers have mismatched GFs and one of them has a lower GF low / higher GF high (e.g., 30/95), the other diver may suffer from a more inefficient decompression compared to his programmed one (e.g., 60/72).

Diving similar and agreed before hand GFs is another practice I prefer to avoid disagreeing underwater during deco.

Agree on this one too. I feel like it's more important to be diving similar GF's than gasses. Both being similar are ideal though.

 

[Blackcrusader]

He’s referring to DIR diving

All my diving is doing it right. I dive, I end my dive and come back alive.
Never had a DCS hit in near 40 years of deco diving. Never had an incident on a deco dive.

In some places I dive you canot even get nitrox. So deco dives are planned on air.

A real tragedy I know to have a longer dive time.

 

[Centrals]

All my diving is doing it right. I dive, I end my dive and come back alive.
Never had a DCS hit in near 40 years of deco diving. Never had an incident on a deco dive.

In some places I dive you canot even get nitrox. So deco dives are planned on air.

A real tragedy I know to have a longer dive time.

Until you got hit!!
If you do not want to get hit then stay away from scuba diving.

 

[Wibble]

Except when it isn't... This woman never exceeded 1.4 and clearly toxed at 145ft on 24/25.

2007-07-14 Incident – IUCRR

iucrr.org

There is a very good reason many folks dive with 1.2 on the bottom or even less.

One swallow doesn’t make a summer.

To tox at 1.4 is “unusual” as there’s literally hundreds of thousands — millions? — of dives done to the old 1.4 & 1.6 rule — the DIR proponents advocate deco on 100% oxygen at 6m/20ft which is 1.6.

We all know that it’s statistics. CNS and POT (pulmonary oxygen toxicity) are well documented with oxygen clock tools.