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By the end of this topic, you should be able to answer these questions: 1 What are the guidelines regarding material and equipment compatibility using enriched air with more than 40 percent oxygen? 2 Does trimix affect equipment choice and compatibility? 3 What are four recommendations regarding equipment maintenance? Compatibility Guidelines As you recall from your PADI Enriched Air Diver course, using gas blends with more than 21 percent oxygen calls for special equipment considerations to avoid fire and/or explosion hazards. As a Tec 40 Diver, you'll be qualified to use oxygen percentages up to and including 50 percent oxygen. Tec 45 Divers and higher use use up to 100 percent oxygen. The higher the oxygen content, the more important it is to follow compatibility guidelines. Any equipment (regulator, valve, cylinder) that will be exposed to a gas with more than 40 percent oxygen, or pure oxygen, at any time (including during blending) must be rated for oxygen service. The equipment must be: Oxygen clean – free of contaminants. Oxygen compatible – made from materials that don’t combust easily in oxygen. Follow manufacturer recommendations regarding use with air, enriched air or oxygen. Some manufacturers require oxygen service for use with gas higher than 21 percent oxygen, and some limit the oxygen percentage, for example up to 40 percent. Note: Some regulators made of titanium may not be recommended for use with high oxygen gases. Always check individual manufacturers' guidance. Photo credit Martin Robson If you expose oxygen service equipment to nonoxygen clean gases or other contaminants, the equipment is no longer oxygen clean or oxygen service rated. For example Using an oxygen service regulator on a standard air cylinder results in the regulator being considered contaminated. Filling an oxygen service cylinder from a standard scuba air source is not good because standard scuba air (Grade E) is not oxygen clean. The cylinder must be re-oxygen cleaned. Leave enriched air/trimix cylinder tags in place for removal by blender. This allows blender to confirm that the cylinder was not refilled by a nonoxygen clean air source. Protect oxygen service equipment from contamination by keeping it bagged and sealed from the environment until needed. Rinse and stow oxygen service equipment as soon as possible after use, and keep it away from areas or exhaust that may have oil or other contamination. The general guideline is to have oxygen service equipment recleaned annually, but check local regulations. Violating guidelines regarding oxygen compatibility carries a severe risk of injury and/or property damage caused by fire and/or explosion. Trimix Apart from suitable cylinder labels and marking, helium mixes do not usually require specialized equipment. As always, check the manufacturer's literature. Take the TecRec Gas Blender courses to learn more about oxygen compatibility and gas blending. Hyperoxic Gases and Equipment In PADI Tec Diver courses, you learn to use gases with more than 40 percent oxygen and/or pure oxygen to extend no stop time and benefit decompression. The use of higher oxygen lessens the risk of decompression sickness, because it is generally believed that for a given a decompression model, a schedule requiring shorter stops is more reliable than a schedule requiring longer stops. Without the high oxygen, you’d face impractically long decompression stops. When a diver can get out of the water quicker, it reduces the exposure to other risks such as hypothermia, getting separated from the boat in strong currents, and so on. Using hyperoxic gases, however, is not without some risk. Outside of issues you’ve learned related to central nervous system and pulmonary oxygen toxicity, the greatest hazard comes from the risk of fire. That’s why, as you’ve learned, any high pressure device coming in contact with a gas with more than 40 percent oxygen (or less than 40 percent if specified by the manufacturer) must be cleaned and dedicated for use with pure oxygen. WARNING: There is a high risk of combustion when titanium is exposed to oxygen. Some scuba regulators are made of titanium and may not be recommended for use with high oxygen gases. Always check individual manufacturers' guidance. Using hyperoxic gases as a tec diver comes down to balancing the risks: the risk of getting seriously hurt or killed due to decompression sickness against the risk of getting seriously hurt or killed due to fire or explosion. Most tec divers believe – and accident data support – that provided you’re using properly cleaned and compatible equipment, not using oxygen is a far greater risk than using it. In the end the choice is yours. The risk of fire and explosion is real and is, yet again, another risk you must personally assume before getting involved in technical diving. To manage and minimize that risk, be certain that any equipment you will use with a gas with more than 40 percent oxygen has been serviced for that use by a qualified professional. Maintenance You rely on your gear for life support. Maintain it according to manufacturer recommendations. Have regulators, valves, BCDs and gauges inspected and overhauled at least annually, or more frequently for heavy use or as manufacturer-specified. Have anything that doesn’t appear to work normally serviced before using it. Never tec dive with gear in anything but top shape and within its design parameters. To do otherwise needlessly raises your risk of injury or death by starting the dive with a potential problem.