DIR- Generic Tdi Normoxic trimix or CCR?

[Rich1280]

My GUE JJ ready to dive with carbon back plate, 3l O2 a 200b, 3l suit inflate with air to 200b and D7s with air at 180b weighed 55kg. No heater pack but with a Focus2 on the belt. It feels easier to move around on your back than a twinset due to the way it is closer to your back and wrapped around slightly.

Rich

 

[Alaskan Scuba Dude]

But they are not the DiR standards.

Says you... tell me about your experience in OC technical diving?

 

[Adobo]

Says you... tell me about your experience in OC technical diving

 

[Nick_Radov]

Some standards are guidance, some are critical. It's down to the diver to differentiate. Gasses are not set in stone: what if the gas mixologist was a bit out -- would you cancel the dive or live with what you have? Obviously depends on the parameters and the dive profile and your flexibility. The wreck's slated at 28m/94ft but it's high tide so 33m/110ft to the bottom: would you dive it on 32% or know that 33m is a perfectly safe PPO2 of 1.38? Or even spending $100+ for the helium to do a 33m dive rather than $10 for 32%. How about diving to 38m/126ft - spend $100+ or $10 for 28%? What if the mixologist's gas booster was out of action and you can't get a full fill of 100%; do an air top and get a full fill of 80% (same deco times as 100%).

Pragmatism. Sadly often missing.

The pragmatic approach is to get your tanks filled and analyze a few days before the dive so that if the mix is wrong there's time to fix it. For most regular tech dives, anything within ±1% oxygen and ±5% helium is close enough.

Another aspect of pragmatism is to always use standardized mixes for depth ranges rather than trying to micro-optimize based on planned depth to 28% or whatever. Occasionally that means using 18/45 trimix on a 38m/126ft dive when the weather conditions make deeper sites inaccessible. Standardized mixes also reduce the risk of gas blending errors.

 

[Marie13]

Another aspect of pragmatism is to always use standardized mixes for depth ranges rather than trying to micro-optimize based on planned depth to 28% or whatever. Occasionally that means using 18/45 trimix on a 38m/126ft dive when the weather conditions make deeper sites inaccessible. Standardized mixes also reduce the risk of gas blending errors.

Your location really plays into standard mixes. In the Great Lakes area, it is very rare for a shop to bank trimix at all. It’s pretty much all custom mixed. If you’re diving OC and have to get custom mixes at current He prices, you’d have to consider if you’re going to pay for extra He to get a standard mix if the dive doesn’t call for that standard mix.

 

[Nick_Radov]

Getting your own He doesn’t help if none is available.

Where is helium actually unavailable? Perhaps something has changed but as far as I know it's still available for purchase at most any welding supply store in the US (although the price may be high). That's how we used to get it before it became widely available through dive shops.

 

[Wibble]

Mixes... Was doing a series of ~70m/230ft dives then was planning last weekend's shallow diving with some seals and plants and stuff. Rather than dump the gas I topped off the diluent with air to get a 16/26 mix, perfect for 20m/70ft max. Of course the weather Gods intervened (wonder if it was me taking a pragmatic approach to mixes) so no diving last weekend.

Managed to grab a space on a 45m/150ft dive for tomorrow. Oooh, the gas will be fine for that too; just change the bailouts.

Next dive after that will be a week of dives down to 75m/250ft, so will need to dump the dil and fill with a suitable mix circa 12/55. Again, change the bailouts to the ali80s.

Do need to get some more 3 litre diluent tanks.

Now have three 12 litre twinsets as banking gas: 100%, 9/75 and air. At least I can get a decent number of dives out of those banks before going to my gas dealer for a wallet-bashing session: helium still available but is getting more expensive.

 

[Marie13]

Where is helium actually unavailable? Perhaps something has changed but as far as I know it's still available for purchase at most any welding supply store in the US (although the price may be high). That's how we used to get it before it became widely available through dive shops.

Your information is badly out of date. This thread will fill you in.

Future of OC trimix

After recently getting AN/DP certified via TDI, I was talking with a local technical instructor regarding additional courses advance my training. I inquired about trimix. I got a response that this instructor / shop doesn't teach trimix, nor do they have any plans do. With the cost of helium...

scubaboard.com

 

[LanceRiley]

Where is helium actually unavailable? Perhaps something has changed but as far as I know it's still available for purchase at most any welding supply store in the US (although the price may be high). That's how we used to get it before it became widely available through dive shops.

Helium in welding shops is breathable?

 

[crofrog]

Helium in welding shops is breathable?

That's a loaded question. The answer is "probably" and the tanks should be vacuumed out between fills, but there aren't the certifications from the gas shops you get with UHP.