It was 19.2% o2 at the point you were waiting. A tad on the low side. (20.9% being the norm). Down at 16% you're getting impaired judgement, 12 or 13% you really start to struggle (die!) pretty quickly.
It's definitely worth learning from this.
Here's my understanding of the situation and where things when wrong.
As second man through the crawl I heard a message from Doug to say that the alarm was going off - Knowing that its set at 20.5 I wasn't overly concerned and shouted back for him to bring it trough to me so i could silence the alarm (I was stuck in the crawl unable to go backwards with the end of the crawl only about 2 meters in front of me at this time). At the other end of the passage i had marc asking if i was going to move forward to show me the next sump that he'd found. What i was now assuming (my mistake) was that doug was still coming through behind me bringing it with him. We shouted back that we were moving on to the sump but this communication obviously didn't come through clearly through the twists and turns of the crawl. By the time we heard the shouts from Doug, we were already heading back.
So what lessons should be learnt?
1) Well in the first instance it shows that a gas monitor is possibly a bit of kit that should be more regularly carried but also that carrying one needs to be managed in the correct way.
2) When a gas monitor is carried it should be carried by the first person - or at very least by a person in the leading group.
3) The person carrying the monitor needs to be able to use it - i.e. know how to silence the alarm and know how to interpret the readings on the display. And to know what the readings mean to make an informed decision. In a working environment any space with less than 20.7% can't be entered. However this would prevent entry to many caves and mines and obviously an informed judgement of risk needs to be made. The effects are as follows:
O2 level Effects
22 % Oxygen enriched atmosphere
20.9% Normal level – Safe for Entry (± 0.2%)
19.5% Oxygen deficient atmosphere
16% Impaired judgement and breathing
14% Rapid fatigue and faulty judgement
11% Difficult breathing and death in a few minutes
4) It was absolutely proper not to follow us in were there was concern. 2 unconscious men is 100% better than 4 unconscious men!
5) Communication.
6) Communication.
7) Communication.
Oxygens for pussys!
Ohh Doug - your coat is in my landy - i'll pm u about getting it back to you.
Great video ian - the suspense was almost worth it!
I'll have a go at uploading the photos from the far side of the crawl to the knowledge bank once i've sent this!
Subject: Caving going wrong .... 
Tue 13 Jul 2010, 4:52 pm
