Emergency Oxygen units

By Robert N. Rossier

Proper care and maintenance is vital to ensure yours is ready for action.

Nobody likes bad news, but sometimes a diving tragedy serves as an important reminder. A fatal dive accident on a liveaboard in the Maldives in 2008 was just such a case. The accident involved carbon monoxide contamination of breathing gas, which caused the death of one diver and injured nine others. Among the disheartening details from the news reports: The shipboard emergency oxygen system was broken, and thus oxygen could not be provided to the victims.

In a diving emergency, oxygen first aid can save lives (See "First Aid Refresher"), but only if the emergency kit is fully charged and in good operating condition. Proper maintenance is vital, especially in tropical environments.

Maintenance Concerns
Emergency oxygen systems do not require an inordinate amount of maintenance, but they do require periodic attention. The problem becomes one of "out of sight, out of mind." Most emergency oxygen systems aren't used regularly, and over time components made of plastic, rubber and other synthetic materials can deteriorate and become brittle. Oxygen systems should be professionally serviced at least every two years, more often if they are used heavily. (For a list of approved service centers, visit DAN Training and Education: Oxygen Fill Stations.)

Beyond periodic professional maintenance, the best practice to ensure the readiness of an emergency oxygen system is to remove the unit from the boat after each trip and completely inspect it. For commercial operators, DAN® recommends a bimonthly check of shipboard emergency oxygen systems.

First, inventory all parts, and make sure all components are available. "Once, on a DAN video shoot for a training program, we asked to borrow an oxygen cylinder from the boat's supply because we ran out and needed just a bit more," says Eric Douglas, director of DAN Training. "It took the crew half an hour to find all the parts to the oxygen unit on board because they had been stowed in various places."

When all parts are accounted for, make sure the components are in good condition and ready for use. Look for these common problems:

Uncharged or empty cylinders — Before heading out on a dive or dive trip, ensure that the oxygen cylinder is full. To be filled, oxygen cylinders must also be hydro-tested every five years, so check the hydrostatic test date as part of the bimonthly inspection.

Corroded regulators and components — Perhaps the single biggest environmental concern regarding oxygen systems is corrosion of the metal parts. The locker of a dive boat represents a harsh environment with plenty of heat, humidity and corrosive salts. "Even the slightest amount of salt air that gets trapped inside a case and then sealed up begins to corrode the equipment," Douglas says. "We've opened up units stored on dive boats that are so rusted and corroded you would be afraid to turn them on for fear they would explode."

To protect an oxygen system from corrosion, store it in a watertight case with a silica gel packet to absorb any moisture trapped inside.

Damaged regulator and control valve assembly — The regulator/control valve is really the heart of the emergency oxygen system, and it must also be kept clean, dry and free from physical damage. Bob Eberly, president of EMS Technologies in Leola, Pa., said one potential problem with the cylinder/regulator assembly is physical damage to the pressure gauge. Mishandling, dropping or improperly stowing the emergency oxygen system can sometimes result in a damaged gauge that may not provide a reliable pressure reading. If physical damage to the pressure gauge or the regulator assembly itself is noted, have the unit repaired.

Damaged or deformed cylinder-regulator seals — Another potential problem with an emergency oxygen system involves the seal between the oxygen cylinder and the regulator assembly. A Public Health Notification updated by the U.S. Food and Drug Administration and the National Institute for Occupational Safety and Health in 2006 revealed that faulty or improper sealshave resulted in at least a dozen regulator fires. At issue were the two different types of seals commonly used in emergency oxygen systems; they have decidedly different characteristics.

One type of seal is a crushable plastic or nylon device designed for a single use. When the regulator is tightened to the cylinder, the material deforms to create a good seal, but the deformation is permanent. If these seals are reused, they require additional torque to ensure a good seal. If they start to leak, the friction caused by the flow of oxygen across the face of the seal can cause ignition.

Many manufacturers recommend a different type of seal, referred to as a "sealing washer," that is designed for multiple uses. These consist of metallic rings encompassing an elastometric element made of a flexible polymer. These are generally more expensive than the crushable seal, but they can be safely reused many times without the need for additional torque to ensure a proper seal. All DAN oxygen units come equipped with this type of "oxygen washer."

Deteriorated delivery masks — Heat and exposure to the elements can result in deterioration and cracking of rubber and synthetic components. "We often see old masks left to harden and turn brown in cases," Douglas says. "Non-rebreather masks are designed for single-patient use and should be kept in their protective bag until they are needed. We often see an old mask wadded up inside the case that was used for training at some point, and that is the only mask available for use in an emergency."
Oxygen System Basics
Emergency oxygen systems come in various sizes and styles, but most incorporate the same basic elements: a high-pressure oxygen storage cylinder, a regulator/control valve assembly and a delivery mask.

The two primary types of emergency oxygen systems for divers are constant-flow systems and demand systems. Constant-flow systems provide a regulated, and in some cases adjustable, flow of oxygen to the delivery mask. Demand systems provide oxygen in response to the user's inhalation, thus delivering a higher percentage of oxygen and wasting less gas. Because treatment needs can vary from case to case, DAN recommends a multi-function system that can provide oxygen using both the demand and constant-flow options.

© Alert Diver — Winter 2010

