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July 2003 Vol. 18, No. 7   RSS Feed for Undercurrent Issues
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The Role of Regulators in Diving Incidents

data from Australia highlight problems

from the July, 2003 issue of Undercurrent   Subscribe Now

In the United States, we don't get complete information about the causes of dive accidents. While DAN provides excellent medical information, when it comes to understanding the causes of accidents, there is no independent evaluation. In Australia, the Diving Incident Monitoring Study collects information and analyzes it, regularly reporting the results in the Journal of the Underwater Medical Society. Here is a synopsis of the last regulator study, authored by Steve Goble and Christopher J. Acott, who show us just how important it is to care for a regulator (we have added the names of certain regulators to illustrate the study and take all responsibility for editorial changes).

* * * * *

While it is inevitable that a regulator can malfunction during its lifetime, good pre- and post-dive maintenance, regular professional servicing, and buying well-designed equipment can reduce the risk.

"Free flowing second stages frequently follow an
annual service. Test your regulator after servicing
and return it if it was done inadequately."

A first stage regulator can use either a piston (e.g., the Scubapro MK25 R380 or the Sherwood Blizzard) or a diaphragm (Aqua Lung Legend and Calypso or APEKS ATX 50) to control air flow. Either can be balanced or unbalanced. The unbalanced piston first stage was developed in the 1950s and with minor modifications is still available. A piston moves within a sealed cylinder to control airflow. When the diver inhales, the pressure drops causing the piston to open the valve and air then flows in. When the flow stops, the pressure increases, overcomes the combined ambient water pressure and booster spring pressure, and causes the piston to close the valve.

As tank pressure falls so does line pressure, making it harder to breathe. In an unbalanced system (such as the Oceanic Alpha 7 SP4), large orifices cannot be used successfully because the size of the diaphragm or piston needed makes the first stage too large and cumbersome. This limits airflow. Balanced diaphragm and piston first stages eliminate the need for high-pressure air to work the valve, so operation is independent of cylinder pressure. The second stage of the regulator reduces the line pressure to ambient pressure so that air can be breathed easily. Most regulators use a downstream valve (like the Scubapro R380); it uses more adjustment to offer little breathing resistance. Upstream or tilt valves (such as the Poseidon Odin), which have the valve seat in the body, are generally harder to breathe from and are prone to chatter as the air passes through the nonreturn valve.

Diving Incidents

Of 426 incidents examined by this study, 52 (12%) involved the diver's regulator. First stages failed. Low-pressure hoses ruptured. One first stage failed because of tank debris. Foreign bodies in second stages ranged from sand and weed to vomit. Free flowing frequently followed an annual service by a diving equipment retailer. In some cases, the mouthpiece came off.

Eighteen, or 34 percent of the regulator incidents, resulted in death. Eleven different problems occurred, including:

o Second stage free flowed
o First stage failed
o High-pressure hose leaked or ruptured
o Foreign body entered second stage
o Second stage allowed the inhalation of water
o Mouthpiece worn and fell apart
o Increased resistance to breathing at depth
o Second stage dislodged from the diver's mouth
o Swivel connector between high-pressure hose and mouthpiece ruptured
o First stage connected incorrectly to the pillar valve
o Moisturizing filter between the low pressure hose and second stage malfunctioned.

Without regular maintenance, no piece of equipment can be expected to last forever. Yet the regulator rarely receives correct routine maintenance. For example, one free flowing second stage was due to a hole in the diaphragm, clearly attributable to lack of maintenance, as were problems of loose mouthpieces.

Regulator manufacturers arbitrarily advise annual regulator servicing, irrespective of use, but there are no governing standards. So free flowing second stages frequently follow an annual service. Divers should test their equipment after servicing and return it if inadequate. Divers should also obtain the service manual for their regulator to check that the service is performed to the manufacturer's specifications, with proper replacement parts.

Inspection of the regulator mouthpiece before each dive would eliminate problems associated with a worn or torn mouthpiece. In some cases, the regulator valve was attached to the tank improperly. Unlike pin-indexed yoke fittings used for medical gases, regulators have no sure-fire way for correct alignment. Check that the yoke is securely fastened.

Some unbalanced regulators perform poorly at depth and with low air pressure, resulting in increased breathing resistance at depth. The question has to be asked, "Wouldn't you think of coming up if you were finding it hard to breathe?"

The Octopus

Thirty-one incidents were reported with alternate air sources, most with the octopus second stage regulator. Nine incidents resulted in death. The problems included:

o When the octopus was used the air was depleted quickly
o Difficulty breathing from octopus and main regulator during emergency air sharing
o Octopus not purged during emergency causing saltwater inhalation and panic
o Octopus placed incorrectly in diver's mouth during emergency
o Octopus/BCD inflator combination difficult to use during emergency ascent
o Octopus regulator/BCD inflator combination caused confusion while trying to breathe from it and deflate BCD at the same time.

A first stage regulator used with an octopus must have minimal resistance and function adequately at depth with low cylinder pressure and under increased workload. This is necessary to meet the high respiratory flow rates required when both second stages are breathed from in unison, particularly if a diver is panicking. Adding an octopus to an inexpensive or inefficient regulator increases the likelihood of a problem.

The combination of a second stage regulator and a low-pressure BCD inflator as the octopus regulator is difficult to use during an emergency ascent and have resulted in confusion while trying to breathe from it and deflate the BCD at the same time.

Finally, use special caution if a dive crew assembles your equipment. Too many of these divers put complete faith in the dive crew and neglected to check their gear before each dive thoroughly.

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