Renting Nitrox Question

[ResortDiver850]

Greetings,

I recently got my PADI Nitrox Cert.

In my certification class, I had to analyze the gas blend, and fill out the tank label
(MOD, max depth, O2 %, etc.), and then fill out a log book before checking out the tanks for my checkout dives.


I went on a charter dive a few days ago. The boat had the nitrox tanks already aboard with just a sticker marked w/ 32%, not the more detailed label. None of the other divers analyzed their nitrox tanks. Is this normal?


Also, a side question. I checked online PADI EAN 32 tables for my dives, and it seemed (assuming I didn't make an error) That I was over my NDL, but my dive computer didn't alarm. Is this normal?

1st dive was 76 ft for 22 min
3 min/15 ft SS
1:00 SI
2nd dive was 62 ft for 38 min
5 min/15ft SS

Thanks!

 

[Killerflyingbugs]

Dive tables are conservative (padi especially) , your computer tracks the whole dive and adjusts for what you actually did on the dive.
I bet that's normal, people are trusting of pros and don't double check.

 

[rombre]

I went on a charter dive a few days ago. The boat had the nitrox tanks already aboard with just a sticker marked w/ 32%, not the more detailed label. None of the other divers analyzed their nitrox tanks. Is this normal?

Especially in South East Asia you often really need to force the staff to let you analyse the gas (or at least watch them doing it). I wouldn't dive with a nitrox tank without analysing it.

 

[rhwestfall]

your tables are based on a square profile dive. it is highly unlikely (as your computes showed) that you actually dove a square profile. Look at (assuming you can) the profile or if your computer gives you the average depth and you will see that it won't match the data you used for the dive tables. The computer calculated the cumulative time and depth exposure ongoing throughout the dive. This can be seen by watching your NDL increase as you work your way back up from whatever depth you were at.

That being said, DO NOT USE AVERAGE DEPTH FOR NDL TRACKING WITH TABLES!!!!

I'd suggest you get a copy (there is a free version) of DivePal and play with it to see what happens with theoretical tissue loading on dives, both single and repetitive. Even the subscription one is only a couple bucks for a year. Great learning tool.

as to not testing the tank, you need to decide what you should do. If you understand the process/QA/QC the supplier of the tanks uses and are comfortable, then dive. Keep in mind, you can buy your own analyzer, of perhaps make arrangements to see the process if you feel you need to validate it.....

 

[halocline]

I went on a charter dive a few days ago. The boat had the nitrox tanks already aboard with just a sticker marked w/ 32%, not the more detailed label. None of the other divers analyzed their nitrox tanks. Is this normal?

Also, a side question. I checked online PADI EAN 32 tables for my dives, and it seemed (assuming I didn't make an error) That I was over my NDL, but my dive computer didn't alarm. Is this normal?

This is a little scary. You're asking questions that are really basic and you should understand the answers having taken the course. Yes you should always analyze nitrox tanks that you are going to use and set your computer for the percentage or O2 that is in your tank. This is one of the most basic safety requirements of using gasses other than air. You should also understand that computers track your actual time/depth and adjust your NDL accordingly. That is the reason people buy and use dive computers.

Don't take any offense, but you should consider going over the material for your nitrox class again and try to better understand what you were supposed to have been taught. If your instructor was a good one, he/she will gladly help you.

 

[mi000ke]

I just did my first nitrox dives after getting certified, and the tanks marked 32 were actually 33. Reduces MOD by only a few feet, but still worth checking.

 

[Neilwood]

Greetings,

I recently got my PADI Nitrox Cert.

In my certification class, I had to analyze the gas blend, and fill out the tank label
(MOD, max depth, O2 %, etc.), and then fill out a log book before checking out the tanks for my checkout dives.


I went on a charter dive a few days ago. The boat had the nitrox tanks already aboard with just a sticker marked w/ 32%, not the more detailed label. None of the other divers analyzed their nitrox tanks. Is this normal?


Also, a side question. I checked online PADI EAN 32 tables for my dives, and it seemed (assuming I didn't make an error) That I was over my NDL, but my dive computer didn't alarm. Is this normal?

1st dive was 76 ft for 22 min
3 min/15 ft SS
1:00 SI
2nd dive was 62 ft for 38 min
5 min/15ft SS

Thanks!

As others have said, your computer will track your theoretical nitrogen better than tables so will account for differences in ascent speed, descent speed, depth (I doubt you were exactly at that depth the entire dive). Quite normal for it to come up with a greater dive time than tables as tables only use MAX depth not average.

With regards to checking - I would always check my tanks for a few reasons: 1) I am responsible for my own safety and if there had been a screw-up I want to know about it 2) good habit to get into and 3) I want to be able to track my O2 especially if I am doing multiple dives. That said, unless you were approaching a 40% nitrox mix (which would have taken a monumental screw-up by the tank monkey), you are no where near MOD with ppO2 @1.4. That is possibly why the other divers didn't check the tanks.

The last boat I was on we had dedicated tanks for the entire week with the divers taking their own regs off the tank, it being filled by the tank monkey, tanks were then checked shortly before the dive and regs put back on. No one marked the % or MOD on the tanks (just on the log) - there was no chance of mixing up tanks as we all had our own stations and the filling whips came to the tanks and not the other way around.

 

[ResortDiver850]

Thanks for the replies. The rental computer I was using was set to AIR by the dive shop so I knew it would be in a very conservative NDL, and the depths of the sites (76ft and 65 ft) were within the MODs of the 32%. I also knew that the computer adjusts for different depths during the dives; giving me a more generous NDL. I would definitely like to get my own analyzer.

I wasn't sure how much of a difference there would be between the tables and the computer. I thought I would just follow the tables for the extra margin of safety than just going by the computer next time. Partly because using a rental computer that I am not completely familiar with is a tad uncomfortable for this novice.

I still have a lot to learn. Just curious how things worked in the real world vs. academic side. The SCUBA people I've dealt with in the real world are a lot more relaxed about things than I have been trained to be. For example, the dive buddies I was paired up with on the boat took off and left me solo!

Thanks again for the help. I am learning that just I need to hold myself to the higher standard that I am comfortable with than what I am observing by the other divers I am seeing.

Much appreciated!

 

[archer1960]

When I was in Coz, the dive op required the nitrox users to analyze (or watch them analyze) and mark their own tanks before signing the log. Then the op carried the tanks to the boat, and each person found their own labeled tanks to set up their gear.

 

[flyingDiver75]

Also, a side question. I checked online PADI EAN 32 tables for my dives, and it seemed (assuming I didn't make an error) That I was over my NDL, but my dive computer didn't alarm. Is this normal?

1st dive was 76 ft for 22 min
3 min/15 ft SS
1:00 SI
2nd dive was 62 ft for 38 min
5 min/15ft SS

What computer are you using? Do you remember your NDL time remaining when you started your ascent?

Tables are pessimistic, even for square profiles -- your actual depths / times seem pretty reasonable. I would expect most computers to give you at least 45 minutes NDL on your second dive having dove similar profiles on both a very conservative computer and a not so conservative computer.

I try to mentally note my NDL remaining at the start of my ascents and add that to my logs. Over time, you can get a good feel for what's 'normal' with your computer for a given set of profiles and for me, that's one more indicator to use during a dive to assess that everything is nominal.