Keep Training
Oxygen Fire
O rings
Regulator Freeze
Question to
Lake Sydney Lanier North of Atlanta

A few words about jobs in the dive industry...
Don’t let your training waste away!
 It always surprised me how quickly the skills that were made second nature during training fade away when not used regularly. It’s very easy for experienced divers to become complacent but since they are the ones doing the advanced diving it’s even more important to stay sharp. Most statistical analysis of dive accidents reveals that the first couple of dozen dives that a diver makes are the most dangerous statistically. This is easily attributable to inexperience. However some analysis reveals another place in a diver’s career when the risk of an incident begins to rise again after the diver has years of experience and over fifty dives. This may be about experienced divers ‘dropping their guard’ just as they dive more advanced environments.

     I fall perfectly into the category of an experienced diver who sometimes takes things for granted. I have to make a point of getting in the water often even if it’s just a pool or lake to keep my skills fresh. But there is more to the experience than just practicing reg retrieval or gas switching drills. It is about the physical aspects like tolerance to narcosis or just the exertion of hauling your double tanks out to the car.
I have no illusions that these training dives can condition my body beyond the destruction of my fast-food couch potato life style but it let’s me know where my limits are. Knowing how far you can really swim is just as important as being able to swim far. So when I show up with my double cylinders, stage bottles and a dry suit at the local mud quarry that’s less than forty feet deep, I answer the strange looks from other divers with any one of a number of smart-ass remarks:
“I carry back-up gear every time I dive.”

“There’s a hole that drops to seven hundred feet right off the beach.”

“I’ll be surfacing next Tuesday.”

“I’m a new diver so I need all this stuff to be safe.”

“The Atlantic Ocean looks so much smaller now that I’m standing next to it.”
Every dive is a training dive for the next dive.
Anatomy of an Incident

Real incidents
Oxygen Fire…
A commercial dive boat operating in the Gulf of Mexico was at dock loading supplies. Oxygen was being received in large tanks plumbed together in racks lowered by crane onto the deck. The oxygen was used in the vessel’s decompression chamber where a separate oxygen system piped it to face masks inside the chamber. The crew member receiving the load didn’t want to go to the usual trouble of stringing hoses across the vessel to the oxygen system so he could check the pressure of the incoming tanks. Instead, he grabbed a much closer back-up supply hose to the surface supply dive system. He would connect the oxygen rack to the dive system, read the pressure at the dive station then move to the next rack. Commercial O2 is delivered at over 2000 PSI and on this occasion the crewman opened the valve on the rack with a particularly quick twist. The compressed gas traveled at almost sonic speed through the fitting to the closed valve on the end of the supply hose. The seating surface in the valve was made of a material compatible for oxygen service but not cleaned for oxygen service. The gas molecules struck the constriction generating tremendous heat and the thin layer of machine oil left in the valve from the production process flared up like gasoline. The Teflon valve seat melted letting the gas slam the supply hose and the next valve upstream. The seat that valve also scorched and melted allowing the oxygen to blast the system upstream, burning two more valves before stopping at a pressure regulator. The flashes were confined within the valve bodies causing no damage to the rest of the system and causing no injuries… this time.

 Respect your gas.
What do you really know about that “O-ring”?

     Most divers only see the o-ring at the valve outlet where they connect the first stage but there are fifteen to twenty o-rings in a typical open circuit scuba system depending on the regulator design and give or take any alternate second stages or gauge consoles. There may be about a dozen that are actually in your gas flow when you’re breathing underwater but it’s okay, they wont hurt you.
     O-rings can be ‘static’ or ‘dynamic’. Static justholds back pressure like at the end of a hose connection. Dynamic o-rings hold back pressure and experience movement like those on a swivel fitting or piston head.

Common O-ring Materials

Buna N – a form of neoprene, cheap, durable but only moderately resistant to chemicals(tastes like chicken)
Viton– Most common in Nitrox regulators because of oxygen compatibility
EPDM(ethylene propylene) - weather resistant, oxygen compatible
Polyurethane– good abrasion resistance, some formulas are oxygen compatible

Hardness (Durometer)

     The hardness or softness of an o-ring is determined by the work it’s going to do. Generally a harder o-ring will last longer but is less forgiving of imperfections in the sealing surfaces allowing leaks. Also, the gap between the sealing surfaces is calculated to account for a specific hardness.

     Any o-ring in any material in any durometer can be made in any color. If it's green that just means it's green.

   These parameters can occur in any combination producing a lot of o-rings that look alike. The only way to really know an o-ring is to know where it came from. Seriously.
Anatomy of an Incident

Real incidents
Reg Freeze-up
Regulator Freeze-Up

     A solo tech diver in twin eighty cubic foot tanks was beginning his ascent from twenty-five minutes at one hundred and sixty feet in a northern U.S. lake in thirty-eight degree water. The diver was aware of cold water hazards but believed that the water was still warm enough not to worry about equipment freeze. He had planned for a forty minute decompression on an air table schedule but carried computers as back-ups and a thirty cubic foot pony bottle of fifty/fifty nitrox as an extra margin. In a careless moment at depth, the diver drew a deep breath from his regulator at the same time he added a small amount of air to his BC. The volume of air rushing from high pressure to ambient pressure formed ice in his second stage and in the valve of the BC inflator mechanism causing both to open and free-flow. The BC inflated uncontrollably and the increased airflow chilled the first stage forming ice in the ambient chamber causing the first stage to open. The rush of fifteen hundred PSI going through the system opened up the alternate second stage which also froze open. With air pouring out of his system, the diver struggled with the inflating BC disconnecting the QD hose but not in time to prevent an uncontrolled ascent. He flooded his dry suit through the neck dam but was still headed for the surface blowing past all his deco stops. The ice in the second stages held open the exhaust valves causing the regulators to spew snow and water instead of air. Under stress and heading for the surface, the diver grabbed another second stage from his other tank and breathed heavily causing that system to freeze open as well. Wrestling with his gear on the surface, he defrosted the free flowing second stages by cupping his hands over the exhaust shroud and exhaling warm air through them. The sunlight striking the first stages helped defrost them but not before the diver lost half of his remaining gas supply. He used his breath to defrost the BC inflator mechanisms but the corrugated hose was packed solid with snow and wouldn’t allow the air in the bladder to escape. The air spraying in from the inflator had frozen the water that always gets into a BC and plugged the shoulder dump and the inflator dump. By squeezing the corrugated hose he managed to break up the ice clogging the hose and finally managed to start dumping air from his BC after a full minute and a half on the surface. There was just enough air in his tanks to complete a computer generated deco schedule of about twenty-five minutes shivering in a drysuit flooded with thirty-eight degree water. The diver suffered no ill effects... not that I know personally... cause it wasn't me... it was... some other guy... yeah.. he moved out of state. Yep.. not me.


Real Diving Questions

Actual questions to dive manufacturers…
“We’ve been diving with your brand of gear for many years but just recently our house burned down to the ground and all the scuba gear we bought was destroyed. Being that we have been loyal customers for years we wanted to know if you would replace our gear to help us get back into the sport we love?”

The interesting thing about this letter is that this person actually included a photo of a burned down house (not any purchase receipts for dive gear or such). Manufacturers do get involved in the community by supporting public service organizations like local police and rescue squads but this is done through the local dealership. I would have sent them to a local dive shop but I thought they should contact their insurance agent first. Turns out, they were hitting up the whole dive industry with the same story.
“I was on a dive around sixty feet and the no decompression limits that my dive computer showed were the same as my buddy’s but my depth was only reading twenty feet!”
More than any piece of equipment, dive computers have had the greatest impact on the way we dive in terms of depth and time. They also create confusion for people who don’t read the owners manual. This computer was set for meters not feet.

More than any piece of equipment, dive computers have had the greatest impact on the way we dive in terms of depth and time. They also create confusion for people who don’t read the owners manual. This computer was set for meters not feet.