Whether it's ignorance, laziness or just a cavalier attitude is hard to tell, but an inordinate number of gas emergencies are caused by hose failures: failures at points that show tell-tale signs of long-term deterioration, and that could have been prevented by a rudimentary inspection and annual service. The classic hot spot is around hose crimps - look for deformed outer hose casings and move or remove hose protectors that cover crimps to get a good view. As you can see in Table 1 a LP hose failure can drain 2200 litres / 80 cu ft of gas in less than a minute and a half, so reaction to a rupture needs to be swift and decisive - switch to a backup gas source and shut down the offending regulator and terminate the dive.
SD! Solo Divina Manual __
A ruptured HP hose actually allows more time to react - counter intuitive perhaps but the tiny apertures on the high pressure side of our rigs make it so. But once again, our reaction should be to switch to a backup gas source (when necessary) and shut down the offending regulator and terminate the dive.
One should also inspect for loose hoses at first and second stage connections (especially if swivels are fitted because these are a "wear" item) and look closely at the SPG. It's also good practice to make sure the Schräder valve coupling at the connection end of all LP hoses - the ones that connect to your BCD infiator and your drysuit and BCD - is corrosion free, clean, working correctly and can be connected and disconnected quickly and easily.
A worn, loose or dirty Schräder valve stem can effectively lock an LP hose in place, which can be a major issue should the first stage decide to free flow. And since this piece of equipment is easy and inexpensive to replace, there's no excuse to dive with a suspect valve.
Two more spots for potential gas loss are the cylinder valve's burst disk and the neck O-ring forming a seal between the tank and its valve.
On the rare occasions burst disks let go, it is mostly during cylinder filling or cylinder storage - usually in a hot environment causing internal pressure to exceed the disk's break point. However, on rare occasions, they have been known to let go while underwater. The most common catalyst is the bolt holding it in place gets knocked: knocked hard! The easy way to avoid this is to be careful not to bump into things, but annual replacement of burst disks (during valve service) is recommended. Several regions of the world use valves without burst disks in them. If you dive in one of these areas, you have one less potential failure point to consider; however, if you travel to dive, always check "rental and local" gear to familiarize yourself with its design.
An extruded neck O-ring is an even more unlikely source of trouble underwater. O-rings sometimes pop out of position after filling a tank or while it is being transported. The most likely cause of a neck O-ring extruding would be the unlucky by-product of severe knock to a yoke-type valve. The level of force to make this happen would be violent enough to move or distort the valve itself and might cause other issues.
Both these types of gas loss are unlikely but sensible divers consider them and plan a contingency action because this type of gas emergency will drain the cylinder completely - and in less than a couple of minutes as seen in Table 1. The good thing to note is they can both be prevented by annually servicing your equipment, properly handling your equipment both in the water and while transporting on land, and being aware of your surroundings while underwater. All of the above are paramount skills required to be a safe solo diver.
The most common cause of gas loss during a dive and the easiest to fix in water are regulator freeflows and yet this is one of the common causes of diver panic and runaway ascents! Regulators can start to free flow for many reasons - cold water, over breathing, poor set-up, overdue service, and because the day ends in a Y - but the solution is a simple one that depends on the gear configuration you have.
In the case of diving with an H or Y valve or a twin set of cylinders, and the diver has two independent first stages is to simply switch to the back up regulator, then reach back and shut down the regulator that is having the issue. Of course with the diver now using their back up, it is imperative that (hey end the dive immediately.
When a solo diver is using a single primary cylinder with a pony bottle the procedure is as simple of switching to the regulator on the pony bottle and shutting down the other tank. And as is the case in any diving equipment problem, when something goes wrong, end the dive i miHcdi^tcly^ «»«o«»«»«»««!««»«»«»«»«»»»»»»«»«®«®«»»»«!»»»!»«
Switching to back up regulators and shutting down simulated free- Simulated freeflow drills llows is a drill one should practice hnuld hp TirarticP until until it becomes second nature and SnOULd Oe pmCUCe UYllU
can be completed while maintaining (f becomes Second nature position in the water column!
The above issues are also the major reasons for a solo diver to carry a completely independent gas source on every dive since the simple remedy for these emergencies is to switch to the pony bottle and surface as circumstances allow - not forgetting to execute a proper safety stop.
Free Flowing / Malfunctioning LP Infflator
A related gas emergency is when a low-pressure inflator
- such as the one on a BCD or Drysuit - freeflows. This type of emergency can be extremely dangerous because the loss of gas is the least of ones' problems. Far more serious in the short-term is that some or all of that gas is flooding into the BCD bladder or drysuit making the diver more and more buoyant.
Reaction to this emergency must be immediate and decisive: disconnect the leaking hose, dump the excess gas from the BCD (or drysuit if that's the problem) and stabilize one's position in the water column. Once that's done, check the SPG and abort the dive, not forgetting to make a safety stop for at least 3 minutes. One additional move for a "bleeding" BC hose is to get the inflator dump open and up. In some models this action directs the bulk of the leaking gas directly into the water and very little goes into the BC. Once this is accomplished, the hose can be disconnected. A leaking LP hose will often stop leaking or slow its leak once it is disconnected, which may mean that shutting down the first stage is unnecessary, but in either case, the dive is over and - usually
- so is the Schrader valve.
Another real issue or concern here is the malfunction or sticking of the inlet valve of the drysuit or the sticking of the plunger of the power inflator mechanism. Once again, proper maintenance is a huge help in preventing this type of problem.
One nightmare that stalks many student divers is that their BC will spring a leak at depth and they will be pinned to the bottom of the ocean, lake, river, or swimming pool like a moth in a display case. For a well-equipped, correctly weighted, and attentive individual, this is pure dark fantasy that they can put behind them.
Part of our pre-dive START drill (more about this later in the dive procedures chapter) is to check for leaks; and if found replace or fix the culprit... and certainly to postpone diving until that's done. So this means that our BC would have to be damaged while diving. Accidents and mishaps come in all shapes and sizes, and some are more likely than others to pay a visit. If you dive, you will experience a free flow at some point. You will have a computer malfunction. You will break a fin strap. You will have a mask break. And you will get disoriented on a dive and surface some distance from where you expected to. Something that is statistically unlikely is that your BC will fail at depth. You may well have a malfunctioning LP inflator, which will require you to orally inflate your BC, but a catastrophic leak is one emergency you are unlikely to experience. And even if you do, there are simple fixes for all but one event.
The most serious BC failure - a tear or puncture of the bladder which provides lift - is the most unlikely. Underwater this would require aggressive contact with sharp metal or rock or a malfunctioning OP valve. The fix is to try to orient oneself so the hole is at a low point. However much of the bladder is above that point will provide lift. This may mean surfacing upright, on one side or another or horizontal slightly head down. Most likely a BC bladder will be punctured on the surface due to poor handling or storage.
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