Safetygram #16 Safe Handling of Cryogenic Liquids Introduction 1. All cryogenic liquids are extremely cold. A cryogenic liquid is defined as a liquid with a Cryogenic liquids and their vapors can rapidly normal boiling point below –240°F (–150°C). freeze human tissue and can cause many The most commonly used industrial gases that common materials such as carbon steel, rubber, are transported, handled, and stored in the liquid and plastics to become brittle or even break state at cryogenic temperatures are argon, helium, under stress. Cryogenic liquids in containers hydrogen, nitrogen, and oxygen. and piping at temperatures at or below the boil- There are a number of general precautions and ing point of liquefied air [–318°F (–194°C)] can safe practices that must be observed because of actually condense the surrounding air and can the extremely low temperatures and high rates of cause a localized oxygen-enriched atmosphere. conversion into gas of for all the cryogenic liquids. Extremely cold cryogens such as hydrogen and There are also specific precautions that must helium can even freeze or solidify the be followed where a particular liquid may react surrounding air. with contaminants or may present other hazards 2. All cryogenic liquids produce large volumes associated with that particular product such as of gas when they vaporize. For example, one asphyxiation or flammability. volume of liquid nitrogen vaporizes to 694 The user of any cryogenic liquid covered volumes of nitrogen gas at 68°F (20°C) at in this Safetygram should be familiar with 1atm. A cryogenic liquid cannot be indefinitely both the general and specific precautions maintained as a liquid even in well-insulated outlined. Safetygrams for individual cryogenic containers. If these liquids are vaporized in a liquids are available and should be consulted sealed container, they can produce enormous for additional information. Please consult pressures that could rupture the container. For www.airproducts.com/productsafety to deter- this reason pressurized cryogenic containers mine which Safetygrams may be of assistance. are normally protected with multiple devices As always, end users should have and be thor- for over-pressure prevention. Common pres- oughly familiar with the Material Safety Data sure-relief devices are a pressure-relief valve Sheet (MSDS) for their specific product. All for primary protection and a rupture disc for operators must be familiar with the in- secondary protection. All sections of equipment structions provided with the equipment that may allow for the liquid to become trapped to be used with the cryogenic liquid. must be protected by a pressure-relief device as shown in Figure 1. The product vented by General Safety Precautions these relief devices should be routed to a safe outdoor location. For products covered in this Safetygram, many of the same safety precautions apply whether the Figure 1 product is in the gas or liquid state. Each cryogenic liquid has its own unique properties. Potential haz- Use of Pressure Relief Device to help ards stem from the following common properties: prevent over-pressurization due to vaporization of trapped liquid. Safety Relief Device Valves Valves 3. Vaporization of a cryogenic liquid, except Use tongs to immerse and remove objects from Special Oxygen Precautions oxygen, in an enclosed area can cause asphyxi- cryogenic liquids. In addition to the hazards of ation by displacing the air. Vaporization of liquid frostbite or flesh sticking to cold materials, objects Do not permit smoking or open flames in oxygen in an enclosed area can cause oxygen that are soft and pliable at room temperature, such any areas where liquid oxygen is stored or enrichment which could saturate combustibles as rubber or plastics, are easily broken because handled. Do not permit liquid oxygen or oxygen- in the area such as workers’ clothing. This can they turn brittle at low temperatures and may break enriched air to come in contact with organic cause a fire if an ignition source is present. when stressed. materials or flammable or combustible substances Although oxygen is not flammable it will support of any kind. Some of the organic materials that and vigorously accelerate the combustion of Personal Protective Equipment can react violently with oxygen when ignited by a other materials. spark or even a mechanical shock are oil, grease, Personnel must be thoroughly familiar with the asphalt, kerosene, cloth, tar, and dirt that may con- properties and safety considerations before being Most cryogenic liquids are odorless, colorless, tain oil or grease. If liquid oxygen spills on asphalt allowed to handle a cryogenic liquid and its associ- and tasteless when vaporized into the gaseous or other surfaces contaminated with combustibles, ated equipment. state. Most liquids also have no color except liquid do not walk on or roll equipment over the spill oxygen, which is light blue. However, extremely The eyes are the most sensitive body part to the area. Keep sources of ignition away for 30 minutes cold liquids and their vapors have a built-in warn- after all frost or fog has disappeared. ing property that appears whenever they are extreme cold of the liquid and vapors of cryogenic liquids. The recommended personal protective exposed to the atmosphere. The cold “boil-off” Any clothing that has been splashed or soaked equipment for handling cryogens includes a full gases condense the moisture in the surround- with liquid oxygen or exposed to high oxygen con- faceshield over safety glasses, loose-fitting thermal ing air, creating a highly visible fog. This fog can centrations should preferably be removed imme- insulated or leather gloves, long-sleeved shirts, and also be formed around cold equipment when no diately and aired for at least an hour. Personnel trousers without cuffs. In addition, safety shoes are release of the cold liquid or vapors has occurred. should stay in a well-ventilated area and avoid any recommended for people involved in the handling Fog clouds do not define the vapor cloud. They source of ignition until their clothing is completely of containers. Depending on the application, special define the area where the vapors are still cold free of any excess oxygen. Clothing saturated with clothing suitable for that application may be enough to condense the moisture in the air. The oxygen is readily ignitable and will burn vigorously. vapors can extend well beyond the fog cloud, advisable. depending on the product and atmospheric condi- Special Hydrogen Precautions A special note on insulated gloves: Gloves should tions. Although fog clouds may be indicative of a be loose-fitting so they are able to be quickly release, they must never be used to define the leak Do not permit smoking or open flames in removed if cryogenic liquid is spilled on them. area and should not be entered by anyone. The any area where liquid hydrogen is stored or Insulated gloves are not made to permit the hands dense fog clouds associated with the handling or handled. All major stationary equipment should to be put into a cryogenic liquid. They will only pro- transfer of cryogenic liquids can obstruct visibility. be properly grounded. All electrical equipment vide short-term protection from accidental contact Care should be exercised so that any clouds do and wiring should be in accordance with National with the liquid. not interfere with vehicle traffic or safety escape Fire Protection Association Pamphlet 50B and/or National Electrical Code, Article 500. Boil-off gas routes. In emergency situations, self-contained breathing from closed liquid hydrogen containers used or apparatus (SCBA) may be required. Handling stored inside buildings must be vented to a safe Special Inert Gas Precautions location. Always handle cryogenic liquids carefully. Their extremely low temperatures can produce cryogenic The potential for asphyxiation must be Liquid hydrogen should not be poured from one burns of the skin and freeze underlying tissue. recognized when handling inert cryogenic container to another, or transferred in an atmo- When spilled on a surface, they tend to spread as liquids. Because of the high expansion ratios of sphere of air. If this is done, the oxygen in the air far as the quantity of liquid spilled and the physical cryogenic liquids, air can quickly be displaced. will condense in the liquid hydrogen, presenting confines of the area permit. They can cool large Oxygen monitors are recommended whenever a possible explosion hazard. Liquid hydrogen also areas. The vapors coming from these liquids are cryogenic liquids are handled in enclosed areas. has the potential of solidifying air which can block also extremely cold and can produce burns. People should not be permitted in atmospheres safety relief devices and other openings, which containing less than 19.5% oxygen without sup- may lead to rupture of the container. Dewars and Exposure to these cold gases, which is too brief to plied air. other containers made of glass are not recom- affect the skin of the face or hands, may affect del- mended for liquid hydrogen service. Breakage icate tissues, such as the eyes. Stand clear of boil- Liquid helium has the potential to solidify air, which makes the possibility of explosion too hazardous ing and splashing liquid and the cold vapors that can block pressure-relief devices and other con- to risk. are released. Boiling and splashing always occur tainer openings. This can result in pressure buildup when charging a warm container or when insert- that may rupture the container. Every effort must be made to avoid spills, regard- ing objects into the liquid. Always perform these less of the rate of ventilation, because it is impos- operations slowly to minimize the splashing and sible to avoid creating a flammable vapor cloud. boiling. Never allow any unprotected part of your body to touch uninsulated pipes or vessels contain- ing cryogenic liquids.