When to dive Nitrox: Wreck Diving

This past weekend I dove two wrecks in San Diego: the Ruby-E (a former Coast Guard Cutter) and the Yukon (a former Canadian Destroyer). Both wrecks are located in the San Diego harbor just a mile or two from Mission Beach. We went out on two boats, the Humboldt on Saturday and the Louis Ann on Sunday. The Humboldt offered nitrox (32% I believe) for both dives for an extra $8/tank, I chose not to partake, while the Louis Ann only offered regular air.

My first nitrox dive was a beach dive and it was rather uneventful. I didn’t notice a difference on a single dive between air and nitrox. However in reflecting on my experience this weekend doing multiple deep dives over consecutive days I recognized I should have been using it. Here are my dive profiles for the weekend:

Dive 1: 97′ max for 31 minutes
Dive 2: 96′ max for 28 minutes

Dive 1: 78′ max for 25 minutes
Dive 2: 77′ max for 34 minutes

When I was filling out my log book and checking my residual nitrogen (manually with my tables) I realized using the conservative (and somewhat outdated) methods it presribes I had exceed my no decompression (deco) times. The max time I should have gotten from my first 2 dives without exceeding the no deco time should have been 20 minutes each. According to my tables when I exceeded my no deco limit for more than 5 minutes I’d have a safety stop of 18 minutes and should have exited the water for 24 hours. Well I wasn’t at ~97′ for the full time which is why my computer is more accurate in this case.

If I was diving on Nitrox O2 32% I would have had 35 minutes before I exceeded my no decompression time and who knows I might have been less tired after the second dive. As I said before my computer is far more accurate than any manual table but it’s always good to play it safe. A teacher’s number one priority is to make sure our students are safe but our number two should be our safety. Next time I do wreck dive’s I’m diving nitrox!