Safetygram 16 Safe handling of cryogenic liquids A cryogenic liquid is defined as a liquid with a normal boiling point below –130°F (–90°C). The most commonly used industrial gases that are transported, handled, and stored in the liquid state at cryogenic temperatures are argon, helium, hydrogen, nitrogen, and oxygen. There are a number of general precautions and safe practices that must be observed because of the extremely low temperatures and high rates of conversion into gas for all the cryogenic liquids. There are also specific precautions that must be followed where a particular liquid may react with contaminants or may present other hazards associated with that particular product, such as asphyxiation or flammability. The user of any cryogenic liquid covered in this Safetygram should be familiar with both the general and specific precautions outlined. Safetygrams for individual cryogenic liquids are available and should be consulted for additional information. Please consult airproducts.com/productsafety to determine which Safetygrams may be of assistance. As always, end users should have and be thoroughly familiar with the Material Safety Data Sheet (MSDS) for their specific product. All operators must be familiar with the instructions provided with the equipment to be used with the cryogenic liquid. General safety precautions can cause a localized oxygen- relief devices are a pressure relief For products covered in this enriched atmosphere. Extremely valve for primary protection and a Safetygram, many of the same cold cryogens such as hydrogen and rupture disc for secondary protec- safety precautions apply, whether the helium have the ability to freeze or tion. All sections of equipment that product is in the gas or liquid state. solidify the surrounding air. may allow for the liquid to become Each cryogenic liquid has its own trapped must be protected by a unique properties. Potential hazards 2. All cryogenic liquids produce large pressure relief device as shown stem from the following common volumes of gas when they vaporize. in Figure 1. The product vented properties: For example, one volume of liquid by these relief devices should be nitrogen vaporizes to 694 volumes routed to a safe outdoor location. 1. All cryogenic liquids are extremely of nitrogen gas at 68°F (20°C) at cold. Cryogenic liquids and their 1 atm. A cryogenic liquid cannot be Figure 1: Use of Pressure Relief vapors can rapidly freeze human indefinitely maintained as a liquid, Device to Help Prevent tissue and can cause many com- even in well-insulated containers. Over-pressurization Due to mon materials such as carbon steel, If these liquids are vaporized in a Vaporization of Trapped Liquid rubber, and plastics to become sealed container, they can produce brittle or even break under stress. enormous pressures that could Safety Relief Device Cryogenic liquids in containers rupture the container. For this rea- and piping at temperatures at or son pressurized cryogenic contain- Valves Valves below the boiling point of liquefied ers are normally protected with air [–318°F (–194°C)] can actually multiple devices for over-pressure condense the surrounding air and prevention. Common pressure 3. Vaporization of a cryogenic liquid, Handling Personal protective except oxygen, in an enclosed area Always handle cryogenic liquids care- equipment can cause asphyxiation by displac- fully. Their extremely low tempera- Personnel must be thoroughly famil- ing the air. Vaporization of liquid tures can produce cryogenic burns of iar with the properties and safety oxygen in an enclosed area can the skin and freeze underlying tissue. considerations before being allowed cause oxygen enrichment, which When spilled on a surface, they tend to handle a cryogenic liquid and its could saturate combustibles in to spread as far as the quantity of liq- associated equipment. the area such as workers’ clothing. uid spilled and the physical confines This can cause a fire if an ignition of the area permit. They can cool large The eyes are the most sensitive body source is present. Although oxygen areas. The vapors coming from these part to the extreme cold of the liquid is not flammable, it will support liquids are also extremely cold and and vapors of cryogenic liquids. The and vigorously accelerate the com- can produce burns. recommended personal protective bustion of other materials. equipment for handling cryogens Exposure to these cold gases, which is includes a full faceshield over safety Most cryogenic liquids are odorless, too brief to affect the skin of the face glasses, loose-fitting thermal insu- colorless, and tasteless when vapor- or hands, may affect delicate tissues, lated or leather gloves, long-sleeved ized into the gaseous state. Most liq- such as the eyes. Stand clear of boil- shirts, and trousers without cuffs. uids also have no color, except liquid ing and splashing liquid and the cold In addition, safety shoes are recom- oxygen, which is light blue. However, vapors that are released. Boiling and mended for people involved in the extremely cold liquids and their splashing always occur when charg- handling of containers. Depending vapors have a built-in warning prop- ing a warm container or when insert- on the application, special clothing erty that appears whenever they are ing objects into the liquid. Always suitable for that application may be exposed to the atmosphere. The cold perform these operations slowly to advisable. “boil-off” gases condense the mois- minimize the splashing and boiling. ture in the surrounding air, creating a Never allow any unprotected part A special note on insulated gloves: highly visible fog. This fog can also be of your body to touch uninsulated Gloves should be loose-fitting so formed around cold equipment when pipes or vessels containing cryogenic they are able to be quickly removed no release of the cold liquid or vapors liquids. The extremely cold material if cryogenic liquid is spilled on them. has occurred. Fog clouds do not define may stick fast to skin and tear the Insulated gloves are not made to the vapor cloud. They define the area flesh when you attempt to with- permit the hands to be put into a cryo- where the vapors are still cold enough draw it. Even nonmetallic materials genic liquid. They will only provide to condense the moisture in the air. are dangerous to touch at these low short-term protection from accidental The vapors can extend well beyond temperatures. Use tongs to immerse contact with the liquid. the fog cloud, depending on the and remove objects from cryogenic In emergency situations, self-contained product and atmospheric conditions. liquids. In addition to the hazards of breathing apparatus (SCBA) may be Although fog clouds may be indicative frostbite or flesh sticking to cold mate- required. of a release, they must never be used rials, objects that are soft and pliable to define the leak area and should not at room temperature, such as rubber be entered by anyone. The dense fog or plastics, are easily broken because clouds associated with the handling they turn brittle at low temperatures or transfer of cryogenic liquids can and may break when stressed. obstruct visibility. Care should be exercised so that any clouds do not interfere with vehicle traffic or safety escape routes. 2 Special inert gas Special oxygen Special hydrogen precautions precautions precautions The potential for asphyxiation must Do not permit smoking or open Do not permit smoking or open be recognized when handling inert flames in any areas where liquid flames in any area where liquid cryogenic liquids. Because of the high oxygen is stored or handled. Do not hydrogen is stored or handled. All expansion ratios of cryogenic liquids, permit liquid oxygen or oxygen- major stationary equipment should air can quickly be displaced. Oxygen enriched air to come in contact with be properly grounded. All electrical monitors are recommended when- organic materials or flammable or equipment and wiring should be in ever cryogenic liquids are handled in combustible substances of any kind. accordance with national fire and enclosed areas. People should not be Some of the organic materials that electrical standards. Boil-off gas from permitted in atmospheres containing can react violently with oxygen when closed liquid hydrogen containers less than 19.5% oxygen without sup- ignited by a spark or even a me- used or stored inside buildings must plied air. chanical shock are oil, grease, asphalt, be vented to a safe location. kerosene, cloth, tar, and dirt that may Liquid helium has the potential to contain oil or grease. If liquid oxygen Liquid hydrogen should not be poured solidify air, which can block pressure- spills on asphalt or other surfaces from one container to another, or relief devices and other container contaminated with combustibles, do transferred in an atmosphere of air. If openings. This can result in pres- not walk on or roll equipment over this is done, the oxygen in the air will sure buildup that may rupture the the spill area. Keep sources of ignition condense in the liquid hydrogen, pre- container. away for 30 minutes after all frost or senting a possible explosion hazard. fog has disappeared. Liquid hydrogen also has the potential of solidifying air, which can block Any clothing that has been splashed safety relief devices and other open- or soaked with liquid oxygen or ings, which may lead to rupture of the exposed to high oxygen concentra- container. Dewars and other con- tions should preferably be removed tainers made of glass are not recom- immediately and aired for at least mended for liquid hydrogen service. an hour. Personnel should stay in a Breakage makes the possibility of well-ventilated area and avoid any explosion too hazardous to risk. source of ignition until their clothing is completely free of any excess oxy- Every effort must be made to avoid gen.