Please correct me if I am wrong but the way I work out the dives and
pressure groups is on the first day No problems.
But on the second day a dive to 29.1 metres for 12 minutes gives you an
ending pressure group of G with a 1 hr and 29 min surface Interval this then
brings you to a B pressure group. So you are starting with a residual
nitrogen time of 6 min for the dive to 25.7 metres for 22 minutes. Adding
the 6 min gives you 28 minutes of total dive time. My tables go from 25
metres straight to 30 metres so useing the rule of playing it safe, we round
25.7 metres up to the 30 metre mark and the NDL is 20 minutes so IF this was
a first dive you would have been 2 minutes over the NDL but being a second
dive the ANDL is only 14 minutes, meaning you went over time by 8 minutes.
The emergency Decompression rules state:
If a no-decompression limed is exceeded by no more than 5 mins, an 8 min
decompression stop at 5 metres is mandatory. Upon surfacing, the diver must
remain out of the water for at least 6 hrs prior to making another dive. If
a no-decompression limit is exceeded by more than 5 min, a 5 metre
decompression stop of no less than 15 minutes is urged (air supply
permitting). Upon surfacing, the diver must remain out of the water for at
least 24 hrs prior to making another dive.
By my understanding you should have made a emergency decompression stop at 5
metres for as close to 15 min or more as possible, not the 5 minutes at 5
metres that I read.
Regards
Jon Mathers
I thought some readers might be interested in this (admittedly long)
record
of a DCI incident that occurred about twelve months ago on the South Coast
of NSW.
Three students were undertaking their PADI Advanced Open Water course.
The
students were a male in his thirties another in his early twenties and a
female in her mid twenties. All were apparently fit although relatively
inexperienced from a diving perspective.
The AOW course was conducted in Merimbula and Eden.over a single weekend.
On
Saturday, the divers completed three dives The first dive off the
Merimbula
Wharf was to a depth of 15.4 metres and the total time in water was 40
minutes. The second dive, two and a half hours later was also at the
Wharf
and was to a depth of 9.8 metres for a total bottom time of 49 minutes, A
further two hours surface interval in which time we had lunch was followed
by a third dive to 7.7 metres for 33 minutes. Following the dives, we
retired to the Merimbula Divers' Lodge for a rest and then a pleasant
evening meal together. All divers were in good shape and in high spirits.
There had been no unusual circumstances throughout the day.
The next day, Sunday, it was planned to complete the AOW course with two
further dives, a deep dive and a wreck dive. The first dive, to the wreck
of the Tasman Hauler, was to 29.1 metres. We commenced our ascent at the
twelve minute mark and slowly made our way up the wreck where we did a
five
minute safety stop at five metres. One of the divers, the younger male,
was
showing signs of being badly affected by the coldness of the water (16
degrees) and required careful monitoring on the safety stop. At the end
of
the dive, we returned to Eden wharf where we all went and had some food
and
drink. Our total surface interval was one hour 29 minutes. We then went
back out to do the wreck dive on the Henry Bolte, a dive site very close
to
the Tasman Hauler.
The diver who had showed signs of hypothermia did not come out for the
second dive. He agreed with the instructor (me) that it would be better
for
him to sit the dive out and he could complete the AOW course on another
weekend. The other two divers went for the wreck dive. This dive was to
25.7 metres and we started our ascent after 22 minutes. The total dive
time
was thirty minutes and again we did a five minute safety stop at five
metres. The dive itself had been unremarkable. There had been no
problems
and it was a slow and relaxed dive. Both divers were in good spirits and
feeling well after the dive although the female was showing some signs of
slight sea sickness on the return trip.
After the dives, the usual debriefs and paperwork were completed and the
group enjoyed a pleasant lunch together.
The subject of flying and driving (back to Canberra) after diving was
raised
and discussed. I advised the students of the PADI recommendations in
regards to flying after diving and emphasised that this was still an
inexact
science. We further discussed the issue of driving back over the
mountains
to Canberra and my advice was to reiterate the PADI view but to suggest
that
each individual diver had to take responsibility for his or her own
decision
in this regard. I further explained that, in my case, I would normally
wait
for about six hours before going over the mountain.
In the event, my partner and I head off from Merimbula sometime later and
the other three divers a little while after us. In the event, the time
between their last dive and the time they hit the foot of the mountains
was
slightly over six hours. About two hours later, I received a phone call
from the female diver telling me that she was at Cooma and not feeling
very
well. I asked about here symptoms and she explained that she felt
nauseous,
had a headache and she had pins and needles. Naturally, I was very
concerned. I instructed her to immediately go to the Cooma hospital. I
immediately rang DAN, spoke with the duty doctor, and he arranged for an
immediate evacuation (by a low flying aircraft) to Sydney. By this time,
the woman's condition was deteriorating and it was becoming very probable
that she was suffering from DCI.
That's the circumstances. What was the result? The woman did indeed have
very serious DCI and she spent several weeks undertaking hyperbaric
chamber
treatment in Sydney. She was not allowed to return to Canberra for
several
weeks, not allowed to fly for several months (meaning she had to cancel a
planned overseas trip) and told never to dive again. For several months
thereafter she continued to have deadness in parts of her hands and arms
and
has experienced other complications as well. Now, after more than twelve
months, she is relatively well but it seems as though she will never
return
to full capacity. As I said, she can never dive again.
Personally, I have gone over the circumstances in my mind many, many times
to see if I could or should have done anything different. Although I am
terribly saddened by the events I do not blame myself for what happened.
We
kept well within the PADI tables and we followed all the rules.
Nevertheless, a fellow human being suffered a very bad injury as a result
of
the diving activity.
I now have the habit of setting all my open water students the task of
examining the dives we did on the Sunday and asking them to see if they
are
'safe' dives according to the PADI tables. Of course, they do satisfy the
tables and the students, having completed the exercise are clear in their
mind that the dives would be ok. I then quietly and gently explain to
them
what actually happened and encourage them to accept that the PADI tables,
like all others and all computer algorithms are nothing more than
statiistical likelihoods. If they follow the rules, they are likely to be
ok but nothing in life, as the diver who got the DCI can attest, is
certain.
I hope others might find this story mildly interesting.
John