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January 2003 Vol. 18, No. 1   RSS Feed for Undercurrent Issues
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Is Your Gear Safe with Nitrox?

at what oxygen content is ignition possible?

from the January, 2003 issue of Undercurrent   Subscribe Now

While Nitrox rapidly continues to gain popularity in the U.S. and abroad, there's a simmering debate within the industry about the maintenance of Nitrox compressors and scuba equipment. The problem is that at some increased level of oxygen in Nitrox, standard compressors and regulators can become flammable. So, the industry requires an "oxygen clean protocol," which specifies components and lubricants that are not flammable and are therefore safe. Yet, some experts believe that the oxygen level currently recommended for cleaning may be too liberal to be safe.

Traditional American compressors and scuba gear are set up for compressed air, which contains tiny amounts of condensed hydrocarbons. The slurry visible in the condensation traps of standard oil-lubricated compressors shows how much oil exists in the compression chambers and thus the output. Only proper filtration removes this oil from the breathing gas. The Compressed Gas Association, a trade organization that develops standards for compressed gas practices, has a safe standard for scuba air (called "Grade-E"): no more than five milligrams of hydrocarbons per cubic meter.

A greater percentage of oxygen increases the risk of oxidation in compressors, scuba tanks and regulators. Oxidation can result in fires or even explosions. Rapid pressurization, such as when a tank is being filled or when a cylinder valve rapidly pressurizes a regulator's first stage, heats the gas. As a result, fires have occurred in fill stations and scuba gear.

Bill High, president of Professional Scuba Inspectors, recounted the case of a San Diego diver whose titanium Atomic regulator caught fire while he was breathing a decompression mix of 78.4 percent oxygen on the beach. Charlie Johnson, vice president of American Nitrox Divers International (ANDI), said the fire melted the diver's wet suit to his body, burning him badly enough to require plastic surgery. Johnson says that Atomic recommends that the titanium regulator in question only be used with mixes of 40 percent oxygen or less. Elliott Forsyth, technical consultant for Oxygen Safety Consultants, Inc. notes that "The construction materials need to be compatible from a flammability standpoint," he states, "and the regulator needs to be tolerant of potential ignition mechanisms." Cleaning alone is not enough.

While oxygen makes up 21 percent of the air we breathe, the most common Enriched Air Nitrox (EAN) mixes have 32 percent oxygen (EAN/32) and 36 percent oxygen (EAN/36). Some tech divers use mixes containing 50 percent oxygen.

Decompression cylinders such as the one in the San Diego tragedy often contain far higher percentages. Bill High notes that some gas mixing processes introduce 100 percent oxygen into the cylinder, then adding the remaining gas to create the desired percentage.

Despite the risk, the benefits of Nitrox (longer bottom times, less deco time, decreased narcosis, and, some divers report, warmer and less tiring dives) have created a spiralling consumer demand that has industry scrambling to adopt standards to allow dive shops and divers to use Nitrox without causing everyone to retool completely.

It has become necessary for Nitrox divers and stations to use Nitrox-compatible materials (that is material with a higher heat tolerance), including o-rings and lubricants. But the next step is to define the level at which Nitrox requires special cleaning of equipment to remove flammab le lubricants and thus reduce the danger of hydrocarbon combustion in oxygen-rich environments.

To Nitrox clean a regulator, it must be fully disassembled, and the o-rings and filter must be replaced with Nitrox-compatible parts. A degreasing solution such as Blue Gold is used to remove old grease and hydrocarbons, and a Nitroxcompatible grease is applied. The entire process should add about $15 to the cost of a standard annual regulator service.

Two factions with divergent opinions have debated the question. ANDI, a Nitrox training agency, proposed that the scuba industry follow Compressed Gas Association guidelines: scuba gear and compressors using EAN with greater than 23.5 percent oxygen should require special treatment. One source of contamination would be simply the CGA Grade-E Air, the industry standard for normal scuba air; the allowable condensed hydrocarbon content is too high. Such a standard, however, would require any diver who planned to switch between Nitrox and compressed air to maintain separate scuba systems for each. That's too much to ask your average recreational diver to swallow.

Most other agencies that certify fill stations and technicians lined up behind a cleaning threshold of 40 percent oxygen, meaning that systems using compressed air or EAN up to 40 percent did not need to be specially oxygen-clean. That would allow recreational divers using the common Nitrox mixes to use air, as well, with Nitrox-compatible regulators.

The Divers Alert Network held a workshop in November 2000 to resolve this debate, engaging most training agencies, several manufacturers and outside experts. DAN published a document saying the consensus was that 40 percent oxygen was an acceptable noncleaning threshold. Charlie Johnson says that the paper, which was not a transcription of the proceedings, left out many contrary arguments. He told Undercurrent that "Some experts outside the scuba industry say the 40 percent threshold is laughable. Some say it's criminally negligent. None say it's appropriate." Nevertheless, it seems to be the de facto industry standard.

Apparently everyone at the DAN workshop agreed on one conclusion: Manufacturers' recommendations for product use must be followed. That puts the responsibility on the manufacturers to test their equipment and to know what environments it can tolerate. It also offers the rest of the industry some protection, because manufacturers' recommendations are used to protect equipment makers, such as Atomic, from liability when their products are misused, as in the San Diego regulator fire. You can bet those recommendations are conservative, or some lawyer isn't earning his retainer.

Even ANDI has dropped its crusade to lower the threshold. "We were taking too many arrows in the back," says Johnson. Instead, ANDI, like the rest of the industry, advises trainees to follow those good old manufacturers' recommendations.

"the fire melted the diver's wet suit to
his body, burning him badly enough
to require plastic surgery."

So before your next Nitrox fill, check the product literature about your tank and regulator and make sure you don't exceed the recommendations. Some equipment is rated for use with air only. Others will state that the equipment as sold (without further modification) should only be used with certain levels of oxygen.

And be sure the shop you buy your gear from knows what they're doing. Mistakes do happen. One Florida shop owner who prefers to remain nameless tells us that last summer she spotted Scubalux Nitrox aluminum tanks being lubricated with silicon grease before being fitted with valves in a local plant. Since silicon has a low flammability point at high pressures, it is not Nitrox compatible, so it's no wonder and probably a good thing that the plant has since been closed.

Finally, if your equipment is a few years old, chances are it's not Nitrox compatible, meaning it has o-rings and lubricants with low flash points. Some regulator casings, such as those made of titanium, may not be Nitrox compatible. If you're planning to use Nitrox regularly (such as on a live-aboard trip), and you want to play it safe, take your regulator to a shop with a certified Nitrox technician and get it tuned and cleaned for Nitrox. Then be sure not to use it with air again until you're through diving Nitrox. This advice goes double for anyone planning to use Nitrox with more than 40 percent oxygen.

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