nitrox MOD/TOD

[wedivebc]

I was diving on a charter boat out of NC recently and I had ordered nitrox for the two dives I was planning. Since they banked 30% and the dives were in the 100 - 120 ft range I went with that mix. As I was filling the nitrox log I asked for a calculator so I could fill in the MOD column. The shop employee said "It's 121" I said "I don't think the MOD for 30% is 121 ft may I please use the calculator?" to which she replied "You're wrong it's 121" . Since I wanted to go diving that day and had better things to do that argue I just marked 143 on the nitrox log and moved my tanks onto the boat. This got me thinking though. Are people being taught to use PPO2 of 1.4 these days when calculating MOD or was she confusing target operating depth (TOD) with maximum operating depth?

 

[The Kraken]

Perhaps she was just confusing?!?!

the K

 

[jonnythan]

I was taught to plan an MOD of 1.4. We were given charts and calculations for the 1.6 limit, but advised not to plan with that as an MOD due to the increased risk.

I've never actually heard the term TOD.

 

[The Kraken]

EAN30:
MOD

PPO2 1.4 = 121'

PPO2 1.5 = 132'

PPO2 1.6 = 143'

the K

 

[El Orans]

I was taught to plan an MOD of 1.4. We were given charts and calculations for the 1.6 limit, but advised not to plan with that as an MOD due to the increased risk.

Ditto.

 

[TSandM]

The NAUI recreational nitrox class that I took early this year uses 1.4 to calculate MOD.

 

[do it easy]

In earlier nitrox classes, I was taught 1.6 was OK for warm water dives, 1.4 for cold/strenous dives.

Generally, I plan 1.4 and only use 1.6 for deco at rest.

 

[Mark Vlahos]

I was taught to plan the dive for a 1.4 ATA, but the MOD was for 1.6 ATA. Remember the M in MOD is Maximum, it is at this point where you begin to cross the line into the "danger zone" for noticibly increased risk for a seizure due to high partial pressures of oxygen.

Having said that, I have also seen some fill log books where they seem to expect the 1.4 ATA depth and not the 1.6 ATA. I just write the depth and the ATA.

Mark Vlahos

 

[miesemer]

From my experience:

IANTD uses the term TOD for your target operating depth for the dive. Which could be anything up to 1.5 PPO2 and is adjusted for conditions or physical factors. IANTD uses MOD as 1.6 PPO2. (This was from Advanced Nitrox and Technical Diver courses, I have not taken the IANTD basic Nitrox class so at that level it may be different.)

PADI uses MOD at 1.4 PPO2 and Contingency Depth = 1.6 PPO2.

DSAT uses MOD for bottom gas/working phase - 1.4 PPO2

I've found most (if not all) of the dive operations I've used, use only 1.4 PPO2 for recreational nitrox diving.

 

[wreckchick]

1.4 for MOD
1.6 for contingency depth
1.2 for working dives

Rachel