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Liquid Oxygen LIQUID OXYGEN General Oxygen is the second largest component of the atmosphere, comprising 20.8% by volume. Liquid oxygen is pale blue and extremely cold. Although nonflammable, oxygen is a strong oxidizer. Oxygen is necessary to support life. Oxygen will react with nearly all organic materials and metals, usually forming an oxide. Materials that burn in air will burn more vigorously in oxygen. Liquid oxygen is a cryogenic liquid. Liquid oxygen has a boiling point of -297.3°F (-183.0°C). Oxygen is often stored as a liquid, although it is used primarily as a gas. Health Effects Normally air contains 21% oxygen and oxygen is essentially nontoxic. No health effects have been observed in people exposed to concentrations up to 50% at 1 atmosphere for 24 hours or longer. Inhalation of pure oxygen at atmospheric pressure or less can cause pulmonary irritation and edema after 24 hours. Respiratory symptoms can occur in two to six hours at pressures above 1 atmosphere. One of the earliest responses of the lung is accumulation of water in its interstitial spaces and within the pulmonary cells. This can cause reduced lung function, which is the earliest measurable sign of toxicity. Other symptoms include fever, and sinus and eye irritation. When pure oxygen is inhaled at pressures greater than 2 or 3 atmospheres, a characteristic neurological syndrome can be observed. Signs and symptoms include nausea, dizziness, vomiting, tiredness, light-headedness, mood changes, euphoria, confusion, incoordination, muscular twitching, burning/ tingling sensations particularly of the fingers and toes, and loss of consciousness. Characteristic epileptic-like convulsions, which may be preceded by visual disturbances, such as loss of peripheral vision, also occur. Continued exposure can cause severe convulsions that can lead to death. The effects are reversible after reduction of oxygen pressure. Extensive tissue damage or cryogenic burns can result from exposure to liquid oxygen or cold oxygen vapors. Safety Considerations The hazards associated with liquid oxygen are exposure to cold temperatures that can cause severe burns; over-pressurization due to expansion of small amounts of liquid into large volumes of gas in inadequately vented equipment; oxygen enrichment of the surrounding atmosphere; and the possibility of a combustion reaction if the oxygen is permitted to contact a non-compatible material. The low temperature of liquid oxygen and the vapors it releases not only pose a serious burn hazard to human tissue, but can also cause many materials of construction to lose their strength and become brittle enough to shatter. The large expansion ratio of liquid-to-gas can rapidly build pressure in systems where liquid can be trapped. This necessitates that these areas be identified and protected with pressure relief. This expansion ratio also allows atmospheres of oxygen-enriched air to form in the area surrounding a release. It is important to note that fire chemistry starts to change when the concentration of oxygen increases to as little as 23%. Materials easily ignited in air not only become more susceptible to ignition, but also burn with added violence in the presence of oxygen. These materials include clothing and hair, which have air spaces that readily trap the oxygen. Oxygen levels of 23% can be reached very quickly and all personnel must be aware of the hazard. Any clothing that has been splashed or soaked with liquid oxygen or exposed to high oxygen concentrations should be removed immediately and aired for at least an hour. Personnel should stay in a well-ventilated area and avoid any source of ignition until their clothing is completely free of any excess oxygen. Clothing saturated with oxygen is readily ignitable and will burn vigorously. WARNING! No smoking, open flame, or source of ignition is permitted within 25 feet of the trailer at any time. When off-loading, no smoking, open flame, or source of ignition is allowed within 50 feet of the vent stack and fill connection. Do not permit smoking or open flames in any areas where liquid oxygen is stored or handled. Do not permit liquid oxygen or oxygen-enriched air to come in contact with organic materials or flammable or combustible substances of any kind. Some of the organic materials that can react violently with oxygen when ignited by a spark or even a mechanical shock are oil, grease, asphalt, kerosene, cloth, tar, and dirt that may contain oil or grease. If liquid oxygen spills on asphalt or other surfaces contaminated with combustibles, do not walk on or roll equipment over the area of the spill. Keep sources of ignition away for 30 minutes after all frost or fog has disappeared. Handling and Storage Oxygen must be separated from flammables and combustibles by 20 feet or a half-hour fire wall. Post "No Smoking" and "No Open Flames" signs. Personal Protective Equipment (PPE) One must be thoroughly familiar with the properties and safety considerations before handling a cryogenic liquid and its associated equipment. The eyes are the most sensitive body part to the extreme cold of the liquid and vapors of cryogenic liquids. The recommended personal protective equipment for handling cryogens includes a full face shield over safety glasses, loose-fitting thermal insulated or leather gloves, long sleeve shirts, and trousers without cuffs. In addition, safety shoes are recommended for people involved in the handling of containers. A special note on insulated gloves: Gloves should be loose-fitting so they are able to be quickly removed if cryogenic liquid is spilled on them. Insulated gloves are not made to permit the hands to be put into a cryogenic liquid. They will only provide short-term protection from accidental contact with the liquid. In emergency situations, self-contained breathing apparatus (SCBA) may be required. (D-3) UNLOADING INSTRUCTIONS FOR OXYGEN, NITROGEN AND ARGON Preparation: 1. Spot your equipment at the customer location in a safe manner and out of the way of customer traffic. Make certain you have enough room to monitor and adjust valves and gauges on the trailer and storage tank. 2. Put on your personal protective equipment. 3. Check your bills to ensure you are at the right location and the right tank, that the tank is properly marked and all unloading equipment is correct for the product you are transporting. If not, do not attempt to unload. Call in for further instructions. 4. Read and record onto the Trip Data Sheet both customer and trailer inch and pressure readings. Pay particular attention to fill marks, pressure instructions and any other instruction on the customer storage tank. Cool Down & Purge: 5. Open and secure rear doors and open side doors (if equipped) for ventilation. 6. Close the road relief valve. 7. Open the pump inlet valve. 8. Open the re-circulation valve. This will allow liquid to flow through the pump and return to the trailer, cooling down the pump to operating temperature. 9. Open and secure unload engine compartment doors. Slide out the bottom tray (if equipped) for proper ventilation. 10. Make sure clutch is disengaged. Place emergency shut off switch to “on” position. Start engine and allow it to warm up at idle. 11. Remove storage tank fill connection dust cap and trailer discharge connection dust cap. Inspect fitting for damage and worn or damaged gaskets. Replace as necessary. 12. Pull one end of the trailer discharge hose from the hose tube just enough to allow connection to the trailer discharge line. Remove dust plug, connect this end of the transfer hose and tap the coupling lugs lightly with a brass hammer to ensure a tight connection. WARNING! Over-tightening can damage valves. Do not use any tool, wrench, persuader or other device to force or over-tighten tank or trailer valves. Report all valve problems immediately. 13. Pull the remaining portion of the transfer hose out of the hose tube, remove the dust plug, connect to tight connection. Do not drop the hose or drag it on the ground. 14. Open trailer discharge valve and customer storage tank purge valve. Purge the hose for a minimum of thirty (30) seconds. Close customer tank purge valve. Open customer storage tank top and bottom fill valves. If the tank is a top fill tank only, it will be noted or possibly the bottom fill valve handle will have been removed. In that case, only open the top fill valve. Prime & Unload: 15. Open trailer pressure build valve a couple of turns. You want the trailer pressure to be at least 10- 15 pounds above the pressure it was when you arrived at the unloading site, but no higher than 30 pounds. When the pump, lines, valves and discharge hoses are frosted over, the cool down process is complete. NOTE: if unloading oxygen, any leaks detected during the cool down process must be repaired before unloading. 16. Engage clutch on pump engine and pull the throttle open to increase the engine rpm’s. 17. When pump catches prime (pump discharge pressure will rise and pump will change pitch), quickly close re-circulation valve and turn on meter. Monitoring: 18. Maintain the trailer pump discharge pressure 50-100 pounds more than the customer storage tank pressure by adjusting the engine throttle. 19. Unless otherwise instructed, maintain the customer storage tank pressure at the same pressure it was when you arrived. To increase the storage tank pressure, start closing the top fill valve and stop when you reach the desire pressure. To reduce the storage tank pressure, start closing the bottom fill valve and stop when you reach the desired pressure. Storage tank pressure should never fluctuate more than 10 pounds above or below the required pressure during the unloading process.
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