Drysuit training class

[muddiver]

Judging by your choice of words (enlighten?) it sounds to me like you don't really want to hear an answer. If this is the way you dive don't take it so personally - I realize that lots of commercial divers dive this way.

PSD is not commercial diving. We've got different rules

sheesh

Its got nothing to do with the exhaust valve BTW

Oh, I am soooo sorry to step into your little kingdom of PTSD!

I guess you don't realize that the rest of the professional diving world (Navy, Army, commercial) see PSD divers as Scuby-Doos that usually don't know what they are doing. Who cares how you do your diving, it's always an EMERGENCY, right?

Have-a-nice-day

And Yes, I was really interested in the theory behind your buoyancy control technique, but WHAT EVER!

 

[bridgediver]

muddiver - Maybe I misunderstood the way you posed the question but using "enlighten us"?? Come on. Most people would just simply ask instead of using patronizing words like that. Since we've never exchanged ideas before I couldn't understand why you'd make such a seemingly hostile remark to something that was in reply to someone else(?)
Being a commercial diver I figured you just got defensive about how commercial divers dive - usually using air in the suit vs a BCD, right? Nothing wrong with it for that form of diving.
Too many people come on here and are immediately defensive because they read something and take it personal. I've found there's no point in even explaining things to these people because they're just looking for a fight. Maybe I presumed too much (wouldn't be the first time) in thinking you were of a similiar disposition? If I did then I deserve what you've dished up in your last post.


And yes, I understand all too well of how some PSD teams are viewed by commercial divers and I can't say I blame you. Unfortunately theres alot of gunslingers out there and alot of them get killed because of poor technique, equipment, training etc. It seems that down there anyone with a lightbar and a scuba tank can call themselves a PSD

 

[Desert Pirate]

I dont want to sound dumb... but Id like to know why not to use the seal to vent acess bouyancy. I always have and have never been told different. I ther is a reason, dont "enlighten" me but please "fill me in"?

 

[cmufieldhockey8]

Correct me if I'm wrong (I'm not a PSD) but I'd assume that if you're diving in contaminated water, you don't want to break the seal and have all the contaminated water come in and eat your flesh or something.

 

[bridgediver]

Be happy to DP.

The previous poster made an excellent point on this in regards to the contaminated water but thats not the big reason. Personally I would risk contamination over an uncontrolled rapid ascent - the lesser of 2 evils BUT proper use of the suit will allow a practiced diver to regain control without doing either.

A well maintained suit with a decent dump valve will dump gas from the suit faster than the freeflowing inflator would put in. So dumping the gas through the exhaust valve is the safest method. The diver merely needs to periodically practice as proper body position is key AND awarenes of the event so that the diver may address the problem early.

The reason why pulling a seal doesn't work is that its not a practical solution that the diver can accomplish within 1-2seconds (any more than that and the diver will likely be rocketing up to the surface).
This should give even the sport diver something to consider if you're diving dry. You usaully will be wearing some sort of glove (dry or wet). Some of these gloves may need to be removed in order to grasp a seal enough to pull it. Is the glove over the wrist seal? (if pulling that seal) = time lost. If the decision is to pull the neck seal the glove STILL may need to be removed in order to grab the neck seal. What is usaully over the neck seal? The hood; would need to be moved/pulled up (also potentially dislodging the mask!) = more time lost.

A PSD geared up for contaminate response (not hazmat) will have dry gloves. Some dry gloves are a struggle to get on and off even with help - pulling these isn't practical. So with the dry gloves in place hopefully we would have the dexterity and TIME to:
a) remove our FFM and go to our back-up
b) pull the dry hood down
c) remove or displace the skull cap
d) attempt to reach through the dry hood to access the neck seal
All this while breathing the emergency back-up without a mask on. Just for a suit free flow. Crazy!

Simpily put, it was one of those things that looked good on paper but wasn't put to practice. try it in the pool for yourself and you'll see. Now maybe a neoprene seal would be easier to grasp and pull but latex seals are the popular choice for most drysuit divers nowadays. These are hard to grab on land let alone the added effect of the squeeze u/w

Hope that helps

 

[Desert Pirate]

I see, I havnt had to dive in contamination... hope i dont have to. and I really havnt liked drysuit diving enought to get used to it. (squeeze) I still dive my 7 mm in 48 deg water. but your input is appreciated

 

[muddiver]

Nice description on why "breaking the seal to vent" will not work. I think that a lot of divers get the (insert you favorite alphabet) recreational SCUBA traing class on dry suits, and a lot of those classes assume that the student would be diving a dry suit either with out gloves, or with cheap pull-ons that don't seal over the wrist. Good point over all. I think the maintanence of ALL of the valves on your dry suit annually is important or you could be with out a way to dump excess air. The wrist seal dump I think originated from what do you do if your dump valve doesn't work. This can happen if you wear the older wooly bear underwear or any thing that slufs off lent.

I am still interested in why the use of the suit for bouyancy is discouraged. I am not looking at it from a commercial diver point of view, just a dry suit diver point of view.

I promis, no more snide comments. (BTY I was a firefighter and a crash rescue specialist for almost ten years).

 

[bridgediver]

muddiver

Good point on the undergarments! I actually quit using my wheezles (goose down?) because I found that they slow the venting of the suit compared to other undies (thinsulate types) - they were damn warm too! All this would depend on the exhaust valve type as well as the u/w.

Sorry to be so presumptuous but the answer to question is really just a question of control. We all need to add gas on descent to maintain our buoyancy. We can either put it in the DS or the BCD.
If we use the BCD, it's a smaller container and the gas won't "move" around so much and there is also (usually) multiple ways to dump gas out in various positions (vertical, horizontal, upsidedown etc) - less chance of air trapping.
If we use the drysuit the gas can move and get trapped in the suit. The only way to vent gas effectively from the suit is the single exhaust valve which requires the diver to be in a certain position. The diver needs to have the skill to accomplish this anayway but the more air in the suit, the more difficult it'll be.
Simpily changing position in the water column will affect buoyancy if there is a significant amount of air in the DS - if moving from horizontal to a vertical position the gas "bubble" in the suit may migrate a few feet "up" even though the diver is maintaining depth. This may be enough to make the diver positive and loose his buoyancy if he's not aware.
Many divers use the suit and have learnt how to manage the "bubble" - for them its probably fine but the learning curve is not as steep and its safer for beginner drysuit users to use the BC for buoyancy, the suit for squeezes

Of course we must add a bit of air to the suit to offset suit squeeze but only enough to keep the squeeze off.
I read somewhere that the reason the rec agencies teach to use the suit for buoyancy vs the BCD is because they believe that the average diver wouldn't have the skill to manage both compartments (BCD and suit). This may be true since most average rec divers can't even clear a mask without loosing buoyancy (the importance of which has been debated long and hard). If this is the case, especially at the level we're talking about, the diver should have buoyancy skills well above average before embarking on a DS class (just my opinion).

You'll find tons of threads in the other forums if you do a search that will debate exactly what I've described. You may find a better explanation in those threads too

The reason why I think it can be different for commercial diving is that you guys perform the majority of your work in a negative state am I right? The importance of being neutral doesn't affect you as much. The goal of the sport diver and the PSD is always to be neutral as we are swimming where you guys may be plotting (walking)


Were you air force? Where at? I did the same job except up in Canada we don't have as many toys (or action) as you guys

 

[muddiver]

bridgediver,

I didn't think about the movement of the air in the suit being that large of a change. And I do think that using both the BC and suit at the same time is unnecessary task loading. The movement of the air in the DS is usually controlled by the exhaust valve being the automatic type. It will vent if you go into a verticle position and then you have to re-establish you volume in the horizontal position afterwords.

No, commercial divers do not all dive heavy. Diving heavy is really only necessary for welding or any work that requires you to stand on the bottom (or a platform, or on a structural member) so you can be steady. Most good and effecient divers wear fins and are as close to neutrally buoyant as possible. If you look at my avitar you will notice I am not wearing a weight belt. In a 5 mil wet suit I am neutral to about 60 feet with a Superlight helmet. That was a piling inspection job.

Marine Corps, I went to the civilian fire academy with some of the boys from Norton AFB before that base was closed. The Corps sends it's crispy critters to the Naval Air Station Millington south of Memphis, TN for crash school.

After that I chased brush fires all over California and the West coast of the U.S. for six years, followed by three years of city fire fighter jobs.

I am a civil engineer now, it's a little safer.

 

[bridgediver]

cool...

I've crossed paths with quite a few US air force FF guys. Can't recall any marines though...

You're right about the auto dump occuring when vertical - usually. Alot of suits also require a sideway tilt in order to achieve this or sometimes even a slight tilt up. There usually is a "sweet spot" thats specific to whatever brand/style of suit. Another thing to ponder is that the diver isn't always vertical (or becomes "compromised" in an odd position - ie feet up)

Thats a good picture of you. Do you guys normally dive wet? I can't really tell but are you wearing a BCD in the pic?