Why does DIR reject quick disconnects?

[-hh]

...The factor of "likelihood" must be factored in...

Sure. I tend to call it "reliability"

But I would suggest that other methods be learned, so that you're not relying on a piece of plastic which can break (with a frequency, I'm seeing, of about 1 in 250)...

1/250's probably from anecdotal sources; IMO, the reliability is much higher, baed on my personal observed reliabilty of some of my own gear. IIRC, when we last discussed this, I calculated them as having demonstrated a MTBF of over 500 hours at a 90% Confidence Interval, or thereabouts,.

QD's are what... $4? Why would I invest $4, and what do I get for the money? LESS system reliability?

That investment doesn't make any sense to me.

Accepting a lower system reliability can be part of a larger system trade-off. For example, accepting a wingnut-attached STA instead of welding it on reduces system reliability, but it avoid the expense of two rigs: you've just traded off some of your reliability potential to save money.

The question is not if your life worth the $500 cost avoidance of a second rig, but rather if your life is worth the very small increase in risk for the $500 it would take to eliminate that failure point.

Yes, that's why I said "of the Romper Room kind" - so that we wouldn't confuse my intended meaning of the word "plastic" with those high quality composites, which are quite a different material.

So then just which QD's are you criticizing? Are they the ones made of HDPE, or are you picking on the glass fiber impregnated ones with UV blockers?

I would agree with you, but I find no problems performing "self-rescues" without any QD's.

Since our last discusion, I've read an "endorsement" from a diver who had a medical condition - - I don't recall if it was arthritis or an injury - - but he found having a QD meant that he didn't have to give up diving because of his reduced mobility. This wasn't for self-rescue, but for day-to-day getting in & out of his gear. Can we agree that this is a fair trade-off?

Now, if you think that a QD is a solution for a drowning victim, then you're seriously off-base. I can list about 500 reasons why someone might become a drowning victim, and the solutions to the problems... But QD's are nowhere in there.

I'm not saying that its the solution...afterall, we have QD's on our weightbelts, yet we still find a huge percentage of dead divers who never ditched their weightbelts.

At best, a QD offers a diver one more option on getting out of his gear for whatever purpose/benefit, at the trade-off that its presence is going to reduce the system's overall reliability slightly. That is a decision that the diver should knowingly make, from an informed position.

If you'd like more information on the correct way to don and doff your rig without using a crutch like a QD...

I saw that video ~3 years ago.

One problem with the procedure illustrated is that it is unsuitable for some diving situations. For example, it assumes and requires that you've already handed off all of your external dive accessories (such as a goodie bag or an UW camera) to your support crew. It also assumes that surface conditions are benign and favorable enough such that you don't need to worry about potentially losing contact with the boat.

Of course, if you're a non-photographer diving an an inland Florida cave, you might not encounter these conditions, so this procedure may be perfectly acceptable.

But please excuse me if I have conditions where it is unsuitable and need to pursue different procedures: neither one of us is "wrong"... merely different.

-hh

 

[-hh]

Nobody's "pooh-poohing" anything, -hh.

On the last dive, my dive buddy didn't fasten a buckle on her gauge properly. As such, it dropped off her wrist halfway through the dive. Was this a system failure, or the lack of proper procedure?

System Failure

If you have a car accident and are killed because you weren't wearing your seat belt, would that be a system failure?

System Failure.

FWIW, it would also be a System Failure if he was wearing his seatbelt, but the seatbelt broke.

The fact that Scubaroo's rig was missing a vital component - was that a system failure, or an oversight on the assembler's part?

System Failure

Body armor is made to absorb the impact of a bullet. Metals don't do this... Sand, cloth, and plastic do.

Today's lesson: All materials afford some degree of ballistic protection (even including air!). Protection increases with the density of the material, until the impact velocity drops down into the transitional range. It is at this point that the material's strength finally becomes a factor.

Insofar as vests, the SAPI used to be steel/titanium but it uses composites today because they're lighter for the same amount of ballistic production. Their trade-off is that they're significantly more expensive.

There's no such thing as a free lunch...you just have to "rack and stack" your requirements and your material solutions' trade-offs to decide what is the least bad compromise.


-hh

PS: An open literature source to get you started on terminal ballistics:

http://www.etca.fr/dymat/html/impact.html

Also, Stevens Institute has a good multipart Graduate class series on the subject as well; this material would be covered in ME-508:
http://www.stevens-tech.edu/catalog/soe_mechanical.html

 

[SeaJay]

Sure. I tend to call it "reliability"

Okay, then... What's the "reliability" of getting struck by lightning?

What's the "reliability" that the stoplight will show green on both sides?

What's the "reliability" that a meteor will drop on you?

"Reliability" and "likelihood" are not one and the same.

1/250's probably from anecdotal sources; IMO, the reliability is much higher, baed on my personal observed reliabilty of some of my own gear.

Really? What... 1 in 500?

...So you have 500 BC's? 500 QD's?

My 1/250 count has come from observations of the gear that comes in and out of the shop that I frequent. It's also based on the few dozen BC's we have in our Rescue Squadron.

If you've got a more reliable source, please let me know.

IIRC, when we last discussed this, I calculated them as having demonstrated a MTBF of over 500 hours at a 90% Confidence Interval, or thereabouts,.

Ah, yes... That's right. You have figured them according to hours in use.

If that's the case, then your sample is one... Your sample is not 500, as you claim. You're talking about one individual QD, in use by one person on one BC. There are not enough samples in your data.

Regardless of what you think the QD's reliability is, *not* having it makes the system more reliable. ANY failure of the QD is one more than if you didn't have it at all.

Accepting a lower system reliability can be part of a larger system trade-off. For example, accepting a wingnut-attached STA instead of welding it on reduces system reliability, but it avoid the expense of two rigs: you've just traded off some of your reliability potential to save money.

Fine. Feel free to weld your rig.

I have a feeling you won't, though... If you're willing to deal with the comparably high failure rate of a QD, then you're not likely to worry much about welding your tanks to your plate.

..we have QD's on our weightbelts...

Pardon?

At best, a QD offers a diver one more option on getting out of his gear for whatever purpose/benefit...

How 'bout describing one? Why would a diver ever try to get out of his gear any other way than "the best way?"

Did you watch Chapter 12? Why would anyone ever need a QD?

I saw that video ~3 years ago.

Might want to watch it again. Might make sense this time.

One problem with the procedure illustrated is that it is unsuitable for some diving situations. For example, it assumes and requires that you've already handed off all of your external dive accessories (such as a goodie bag or an UW camera) to your support crew.

I don't have any problem doing the procedure with my underwater camera and goodie bag, and I don't even HAVE a support crew.

It also assumes that surface conditions are benign and favorable enough such that you don't need to worry about potentially losing contact with the boat.

Actually, it assumes that you enter the boat with your gear on, but the procedure works equally well in the water too.

At the 11 second mark of Chapter 12, GI3 dons the rig without any QDs, and without going over the head. At 17 seconds, he doffs it over the head. Then he replaces it. At 28 seconds he simply shoulders out of it, saying, "...or you can just... You know... Get out of it..." He demonstrates at least two methods of donning and doffing which can be performed in the water or on the surface.

Remind me again why a QD is needed.

Of course, if you're a non-photographer diving an an inland Florida cave, you might not encounter these conditions, so this procedure may be perfectly acceptable.

In case you haven't looked lately, I have tons and tons of DIR footage that was taken by an u/w photographer/videographer. A DIR photographer/videographer. More than half of them are saltwater dives from a boat (ie: not in a Florida cave).

The beauty in the DIR system is that you don't need to "consider what sort of conditions you're in," and you don't need to "change everything the moment that a different condition exists." This thought process of, "Well, that's fine for THAT circumstance, but for MY circumstance it's different," is only surpassed in silliness by the words I once heard an instructor say to me: "The water's different around here."

To this day, I still make "around here" jokes with him.

But please excuse me if I have conditions where it is unsuitable and need to pursue different procedures: neither one of us is "wrong"... merely different.

-hh

*sigh*

 

[SeaJay]

System Failure



System Failure.



System Failure

You don't write error messages for Microsoft, do you?

Apparently you are including the individuals surrounding the "system" as a part of the "system."

I would consider the breaking of a seatbelt a "system failure," while I would consider the lack of using one "operator error." To call them both "system failure" does nothing to offer a suggestion for a solution, and helps a solution-seeker to misdiagnose.

If you called that situation "system failure," then a correct solution would be to address a problem within the system - the result would be automatic seat belts or something similar.

That's not the solution.

 

[-hh]

My 1/250 count has come from observations of the gear that comes in and out of the shop that I frequent. It's also based on the few dozen BC's we have in our Rescue Squadron.

If you've got a more reliable source, please let me know.

The problem with your observation is that you have incomplete data. Specifically, for all of those BC's that you see, how many dives (or hours of diving) did they have?

For example, if they were all tropical vacation divers, they probably do 25 dives...call it ~20hours ... per year. At one in 250 failure on a per-year basis, that's 1 failure for every 5000 hours of diving. Is that level of reliability good enough yet for you yet?

Regardless of what you think the QD's reliability is, *not* having it makes the system more reliable. ANY failure of the QD is one more than if you didn't have it at all.

Sure.

Fine. Feel free to weld your rig. I have a feeling you won't, though...

Actually, that's not my point: my point is to point out the glass house that the QD "Rock Throwers" are living in when they criticize the trade-off decisions made by others, yet overlook one that is just as philisophically grevious.

Pardon?

My point is that our weightbelt buckle is a "Quick Disconnect".

How 'bout describing one?

Diver misjudges the size of a restriction and gets himself wedged.

Remind me again why a QD is needed.

It very well may not be. Remind me again why a QD is "never, ever, ever, ever" needed.


-hh

 

[-hh]

You don't write error messages for Microsoft, do you?

Apparently you are including the individuals surrounding the "system" as a part of the "system."

If there's a human involved, yup.

I would consider the breaking of a seatbelt a "system failure," while I would consider the lack of using one "operator error." To call them both "system failure" does nothing to offer a suggestion for a solution, and helps a solution-seeker to misdiagnose.

If you called that situation "system failure," then a correct solution would be to address a problem within the system - the result would be automatic seat belts or something similar.

That's not the solution.

There's the system, then there are subsystems, one of which are procedures, which includes human perception and performance.

The entire field of Human Engineering deals with how to make accomodations in the "hardware" subsystem to compensate for shortcomings on the "human" subsystem.

Probably 99% of our diving deaths are due to human error, not hardware failures. As such, its a bit insane to get all worked up over a single component such as a QD as the most evil thing in the diving world. If you want to be a safe and effective rec diver, concentrate on the big stuff and don't sweat the small stuff...back in the day before they called themselves DIR, this was referred to as "Chasing Unseen Demons". IMO, this wisdom seems to have gotten forgotten over the past 3-4 years.

Gotta run,

-hh

PS: I edited an addition onto the ballistics bit above...you might have missed noticing it.

 

[MikeFerrara]

I like my one piece harness but I haven't seen a busted QD yet.

 

[pipedope]

The system includes the people involved.

The people are nearly always the least reliable part of the system. Ever hear of Three Mile Island? Do you know why there was a meltdown of the reactor core? The 'people' overrided the computers and automatic systems.

We all have pet peaves and hot buttons and they usually have nothing to do with reality.

Lots of discussion about QD but what about divers doing radical decompression, and often experimental at that and without a chambe on site. This seems to me to be a MAJOR risk, far more than the difference made by having or not having a QD in the harness.

People jumping out of airplanes have QDs in their harnesses. I haven't heard of that being a problem. I don't think that a QD failure is any less dangerous in a parachute jump than in a dive. Do you?

I think that the best arguements against a QD in the harness are more about placement of D rings and rigging of backup lights and stage bottles than reliability.

 

[SeaJay]

At one in 250 failure on a per-year basis, that's 1 failure for every 5000 hours of diving. Is that level of reliability good enough yet for you yet?

No.

Look, I'll agree that the failure of a QD isn't a common thing, but I've seen plenty of duct tape on BC's where QD's used to be.

...But I have never taken a stance that QDs are inherently evil or that they are gonna kill someone. My stance is that they're unnecessary, and wholly pointless. You disagree. You have yet to make a point *for* them... You seem bent on just making sure that I don't have a case *against* them.

The bottom line is that there's not a reason why you'd want to have any sort of unecessary device on your life support system - particularly if it's made of breakable plastic.

Actually, that's not my point: my point is to point out the glass house that the QD "Rock Throwers" are living in when they criticize the trade-off decisions made by others, yet overlook one that is just as philisophically grevious.

Right... Therein lies the big reason why we aren't connecting here. I'm trying to make a point that QD's are unecessary and in fact, undesireable, and you're trying to make some sort of larger, political statement about "rock-throwers."

Watch the video again and then consider - why would you want unecessary devices on your life support system?

My point is that our weightbelt buckle is a "Quick Disconnect".

Ah, I see... More problems in the definitions.

I don't think having a weight belt buckle (I don't think that anyone else was considering this when they said "QD" either) on a shoulder strap would be very DIR either.

But hey, man... Feel free to put little QD's all over your rig, anywhere you want...

Probably 99% of our diving deaths are due to human error, not hardware failures. As such, its a bit insane to get all worked up over a single component such as a QD as the most evil thing in the diving world.

Ah, that's where you and I can finally come together. I agree wholeheartedly.

DIR - the subject of this thread - isn't about GEAR - it's about a system, who's major points are in SKILLS. It's got little to do with QD's... So we agree completely.

We see the problem, however, in that things like QD's tend to offer solutions that are GEAR-centric rather than SKILL-centric. Thus, they encourage many divers to utilize computers, spare airs, QD's, integrated weight systems, and the like to solve their underwater problems rather than simply learn the simplest, most reliable way.

...And this results in a heavy distaste not for the QD, but for the things that it stands for. I see soooo many CF's underwater with divers who have "all the latest stuff" that it's numbing. Split fins, short hoses, masks with 50 gazillion windows... Man, I gotta quit before I get worked up over this.

...So it's not that QD's are gonna kill someone... It's not even that I don't agree with the use of them (even though I don't) - It's that people are looking for solutions in the wrong place.

...And frankly, calling EVERYTHING a "system failure" only makes it worse.

At least, that's my opinion... YMMV.

 

[SeaJay]

People jumping out of airplanes have QDs in their harnesses.

Where?

http://www.callmewanderer.com/skydive/jan2002/recovery.jpg

http://www.callmewanderer.com/skydive/jan2002/after2.jpg

http://www.callmewanderer.com/skydive/jan2002/free_f2.jpg

Not a plastic QD anywhere that I can see...

I climb communications towers for a living... And none of my harnesses have a plastic QD anywhere.