Single Point Failures

[OutlawCaver]

I am analyzing single point equipment failures in the most typical backmounted cave diver configuration that I see at most common dive sites. I define single point failure as one in which you have no redundant alternate. Please let me know if I have missed any. I realize that other equipment configurations may eliminate some of these failure points. At this point I am only interested in the backmounted, manifolded, drysuited cave diver.

Thanks

a) Drysuit as used for exposure (seals, zippers, seams, valves)

b) BC (buoyancy cell, corrigated hose & clamp fittings, inflation/deflation device, exhaust valves)

c) Fins (strap, springs)

d) SPG & hose

e) Manifold isolation valve & cross over piping

f) Tank bands & bolts

g) Harness (backplate, straps, webbing & buckles)

Assumptions made:

Spare mask is carried
LP inflator hoses are compatable with both drysuit and BC inflators
Single bladder or bladderless BC is used
Drysuit is an undesirable buoyancy device
Brain is working fine (can't assign a probability of failure to it anyway)

[Bill Rotella]

I had first stage failures twice, once in Mexico, and the other at Telford.............Thank God they were both out of the water. You should also add second stage free flow failures.

[FW]

I had first stage failures twice, once in Mexico, and the other at Telford.............Thank God they were both out of the water. You should also add second stage free flow failures.
I think he is talking about single point failures. You *should* have two regulators anyway :-)

[aainslie]

...Then shouldn't drysuit and BC be dropped off the list since both are buoyancy devices?

Fins too - as I've learned the hard way, one is enough to exit the caves!!!

[sskasser]

Go sidemount and you can drop off items D-F as well.

Granted this only applies to Florida caves, but I would strike "a)" as well. I had a wrist seal go at the beginning of a dive, flooding the whole suit, and since I wear Polartec undergarments, I continued the dive and never got cold.

This DEFINITELY doesn't apply to Missouri caves.

[OutlawCaver]

No way I am pushing on with a flooded drysuit. Loss of trim and with a potentially extensive deco obligation, I am out of there. In 1989, I had a complete drysuit flood when a boot split open in a Leon Sinks passage. With a 40 minute swim out with depths to 150, black silt floor and 60 minutes of deco, my dive was over. Regardless of whether it creates a situation for which you call your dive, it is still a single point failure.

[ARY]

h) diaper. i had at least one dive when i turned on thirds of its capacity :-)
Seriously - you can not use fins effectively on long distance swim.

[Gary]

You should also add second stage free flow failures. I think he is talking about single point failures. You *should* have two regulators anyway.
I was gonna say "second stage free flow" anyway because his assumptions didn't say that he'd be able to reach his valves at all times. What is it? 30 sec to drain an 80? Bad news if you're stuck in a restriction when this happens (with a manifold).


You should throw out "SPG & hose" though. There is not enough air lost thru them to support a swimming diver. It'd be a concern worthy of turning a dive on but not critical.

[skip]

lp hose failure is more serious than the hp hose failure, so maybe lp hose should be added/kept on list? but honestly, i don't really know what a single-point failure is. clue me in please. thanks.

-skip

[MichaelAngelo]

The first and second stages on your deco bottles are both single point failures since their single and none redundent. However the regs on Your back gas aren't since You have a back up.
Did a deco on 50% in 39 degree water few years back with a second stage free flowing from a freeze up. Spent 20 minutes turning the tank value on/inhale , value off/exhale, turn tank on/inhale...
Luckly I had a good Trimix instructor up in Wisconsin who drilled me on being able to do this so when I had to do it for real it was far easier.

[Gary]

Spent 20 minutes turning the tank value on/inhale , value off/exhale, turn tank on/inhale...
I swapped out a disfunctional deco reg for one of my stage regs once. If you use all DIN (or all yoke) it's reasonable to swap one out if you are at rest.

Good point though about deco bottles as failure points. Back up is important (though Kathleen proved to me we could efficiently share air from a deco bottle).

[sskasser]

Once you've had to swap out a reg underwater, do you service it before using it again (the good one, the bad one is pretty obvious)?

[Daedalus]

http://content.imagesocket.com/thumbs/300px_Human_brain_NIH7ae.jpg (http://imagesocket.com/view/300px_Human_brain_NIH7ae.jpg)

[MichaelAngelo]

I could have switched out the free flowing reg on my 50% bottle with the reg on my o2 bottle but then I would have had to switch them back at 20 foot stop. This would have addeded deco time in 39 degree water. Hypothermia is always a factor in the Great Lakes. This is the reason we drill turning the bottle on and off. If drill, far easier. I have switched out regs in caves and it is far easier to swap regs on the bottles in a cave then free floating in open water.
Actually the reg that free flow was just back from service. I had adjustments made on the IP. Freeze ups happen in water this cold, no matter how well serviced gear is.

[Gary]

Once you've had to swap out a reg underwater, do you service it before using it again (the good one, the bad one is pretty obvious)?
Yes.

[michael-fisch]

Once you've had to swap out a reg underwater, do you service it before using it again (the good one, the bad one is pretty obvious)?

Only if it's not a piston 1st stage. For that reason I try to avoid having an excess number of Apeks 1st stages (I have 4), Scubapro MK20 1st stages dont care about getting wet and I have less problems with my 14 MK20s than I do with the 4 DSTs.

Michael

[Gary]

A lot of regultors also have a metal mesh particulate filter on the input. I think if this gets wet it should be replaced cause it's likely to rust and cause problems.

I also think anytime the internals of a reg are exposed to salt water it sould be serviced also (regardless of how it's made) or if the water isn't extremely pure spring water.

But basically if you swap a reg due to reg failure and then DON'T service it afterward you're probably setting yourself up for problems later. If it's a reg you care about I'd get it serviced.

[mgersch]

burst disk should be on the list.
That one always really sucks.

[OutlawCaver]

I don't consider a burst disk a single point failure if you have a functioning isolation valve. A lp hose or regulator are not single point failures if you have 2 of them separated by a functioning isolation valve

[Jay]

What is your basis for single point failure? Such that you cannot get out on your own?

Out of that list, I would only consider the manifold, fin and drysuit (exposure) as true single point failures. The drysuit/bc should always be considered back-ups to each other for bouyancy. If you cannot maintain enough bouyancy with either to swim out and deco then you need to take a drysuit course, reconfigure your equipment or use a redundant wing.

The manifold is self explanatory.

The fin, though some folks can swim with only one, could be very significant based on the cave and distance.

All the other issues should be self manageable for a competent diver and of little concern with a competent buddy. (of course, the dive should be turned.)

As someone mentioned earlier I believe, you need to plan your gas so a single deco gas failure (total or significant loss of the gas) does not prevent you from decoing successfully. If you rely on using your buddies gas in that event, then loss of deco gas would be a single point failure in case of seperation or other circumstances.

[freddie]

hi guys remember you can always use line from your spool as a quick fix for straps on your fins...........

[MichaelAngelo]

using line to fix a strap or being able to swim out with a flooded suit or being able to fix a free flowing deco reg doen't make it NOT a single point failure. It means we are trained to solve problems. It means we used our minds to avoid an incident.
Michael Angelo

[David Brock]

Gas composition. If using air then you should consider contamination at the time of filling. If using mixtures then there are several points of potential failure.

Time / depth calculation. Depending on your watch, depth gauge and computer setup. There are cases of single point failures during decompression incidents that have lead to injury and death.

If you extend this from personal equipment to equipment in general then you should also consider fixed aids for entry or exit of the water and the line.

DPV failure (if not using two scooters).

Knife failure. Following a line entanglement fatality in my group I now know a lot of divers who carry two cutting tools.

Communication devices. In buddy diving, a failure of communication can send you both down a fatal route. Also consider the effects of surface communication failures in the event of a potentially recoverable emergency.

I would recommend reviewing past incidents at both:
http://www.cavediver.net/irap/irap_frm.htm
And:
http://www.cavedivinggroup.org.uk/IncidentReporting/incidentshome.html

You can also review a systematic assessment of potential failures at:
http://www.cavedivinggroup.org.uk/Articles/RiskAssessmentFinal050905.pdf



Don’t get paranoid about potential failures. The most likely cause of death is sitting on the couch in front of the TV eating chips.

Enjoy your diving,

David

[FW]

The most likely cause of death is sitting on the couch in front of the TV eating chips.
Too true :-)

[chimie007]

G

You can also review a systematic assessment of potential failures at:
http://www.cavedivinggroup.org.uk/Articles/RiskAssessmentFinal050905.pdf



Nice link. I like the fact that they have a preventive vs mitigation actions for potential failures. This would make a good tool for teaching.

[David Brock]

You might also be interested in FRIPS (Formal Risk Identification in Professional SCUBA):

http://www.hse.gov.uk/research/rrpdf/rr436.pdf

It is not cave diving specific but introduces a logical framework with diving examples for the consideration of risk.