BSAC Adv Nitrox course

[tiewrapdiver]

Hi guys,

I'm teaching the oxygen and human phsyiology lecture and i'm a little confused with tracking the UPTD's.

It says that the UPTD's dont clear until the end of the dive period and a 24hr break, and that the maximum allowed is 300 in any 24hr period.

Does this mean that UPTD's for a dive will clear after 24hrs or that will they still count until all diving has stopped for 24hrs?

Thanks,

Tim

[turbanator]

Originally Posted by tiewrapdiver

Hi guys,

I'm teaching the oxygen and human phsyiology lecture and i'm a little confused with tracking the UPTD's.

It says that the UPTD's dont clear until the end of the dive period and a 24hr break, and that the maximum allowed is 300 in any 24hr period.

Does this mean that UPTD's for a dive will clear after 24hrs or that will they still count until all diving has stopped for 24hrs?

Thanks,

Tim

They are considered to accumilate for the entire mission.
The REPEX table (printed in the BA-AC adv diver book) gives a sliding scale, i.e. the shoter the mission, then more are allowed on a daily basis.
From memory it's about 850 for a single exposure going down to 300/day by the time you get to 10 or 11 days.

I tend to demonstrate that with a fairly agressive sport diving week, say 2 to 3 dives /day for 6 days at Scapa then it'd still be hard to get close to the limits if you stick to the ADV EANx guidlines - (1.4 or 1.44 max pO2).

WRT the 24 hour clearing - one recommendation is to take a 1 day break every 3 or so days, the implication is that the mission still continues, so I would say that, no, a 24 hour break does not reset the utdp counter.

hth

Paul

[Nick Kay]

Fo simplicity's sake, BSAC's take is you have a max of 300 for any un-broken period of diving.

A period of diving is only broken when you have a 24hr "gap"

Therefore if you were to accumulate 100 UPTDs on each of 3 consecutive days, you'd need to have day #4 as a "break"

However if you look at the RepEx Table, you'll see that there's alot of safety margin built-in

My understanding, is that BSAC did it this way so you wouldn't have to know/remember how many consecutive days diving meant what exposure was allowed (i.e. carry a copy of the RepEx table around with you)

Don't forget, that in addition:
1. You're racking up lots of N2 so your no-stop times are going to diminish as you go through the week
2. Your body core temp drops with each dive (UK especially) and that typically by the end of a weeks diving your body core will have dropped by 1-2C and you need to get the heat back into the core - you're getting hypothermic (dangerous in itself) and cold increases the risk of DCI

Therefore in addition to the UPTDs, there are lots of other good reasons to take a break

[tiewrapdiver]

Cheers guys.

[turbanator]

Originally Posted by Nick Kay

Fo simplicity's sake, BSAC's take is you have a max of 300 for any un-broken period of diving.

A period of diving is only broken when you have a 24hr "gap"

Therefore if you were to accumulate 100 UPTDs on each of 3 consecutive days, you'd need to have day #4 as a "break"

However if you look at the RepEx Table, you'll see that there's alot of safety margin built-in

My understanding, is that BSAC did it this way so you wouldn't have to know/remember how many consecutive days diving meant what exposure was allowed (i.e. carry a copy of the RepEx table around with you)

As I understand it, the simplification was to drop the sliding limit in favour of a 300 UPTD per day, as opposed to the 850 or so allowed for 1 day's diving, 700 for 2, 620 for 3 etc.

r
Paul

[Gareth J]

Originally Posted by Nick Kay

Fo simplicity's sake, BSAC's take is you have a max of 300 for any un-broken period of diving.

A period of diving is only broken when you have a 24hr "gap"

Therefore if you were to accumulate 100 UPTDs on each of 3 consecutive days, you'd need to have day #4 as a "break"

However if you look at the RepEx Table, you'll see that there's alot of safety margin built-in

My understanding, is that BSAC did it this way so you wouldn't have to know/remember how many consecutive days diving meant what exposure was allowed (i.e. carry a copy of the RepEx table around with you)

Section deleted

Hi Nick

This isn't quite the case.

Yes the BSAC tried to simlify things by saying 300 UPTD's per day, rather than the sliding scale of single 1 day exposure, 2 day exposure etc.

The 300 units per day will run indefinately for all consecutive days diving until a 24 hour break occurs, i.e for a weeks continuous diving, a months continuous diving etc. (Not that I am recommending this.)

There are two methods for the interpretation of 300UPTD per day.

Method 1
Start time
09:00 hrs day 1, dives can start & continue (UPTD clock) as long as no more than 300UPTDs are accumulted by 09:00hrs day2
09:00hrs day 2 - clock zeroed - another 300UPTDs available through to 09:00hrs day 3
Continuous as for day 2.

Method 2
Start time
09:00 hrs day 1, dives can start & continue (UPTD clock) as long as no more than 300UPTDs are accumulted by 09:00hrs day2
09:00 hrs day 2, dive planed for 11:00 hrs day 2.
Discard all previous dives up until 11:00 hrs day 1 (24 hours PRIOR to planned dive) as long as the planned dive & the previous dives do not exceed the 300 UPTDs then the dive is 'safe'.
Use this previous acrude UPTD method for all subsiquent dives within the 24 hour period.

Method 2 is the more conservative & less used method, which I used to prefer. (Acquiring my YBOD means I am now more likely to exceed the 300 limit). Method 1 is the more common approach (its easier to apply).

Remember the REPEX table/clock was developed by Bill Hamilton originally. As he stated he made initial assumptions, but no specific testing was made to develop the rules. They have just been applied ever since & become the standard (there was a thread on here previously with alot of this information including Bill Hamiltons original data).

There are other problems to take into account (as stated previously), with uniterrupted diving. Nitrogen loading, Oxygen induced Visual disturbance, earproblems etc.

[Nick Kay]

Hi Gareth

B****r - just re-looked at my "explanation" which was OK until I threw in the 100 per day example.

Note to self - make sure you re-read something once you've typed it

[Gareth J]

Great the web - all our mistakes published for the world to see!!!!!!!