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. Clothing saturated with oxygen spills, regardless of the rate of ventila- is readily ignitable and will burn tion, because it is impossible to avoid vigorously. creating a flammable vapor cloud.

3 Containers Cryogenic liquid cylinders Transfer lines Cryogenic liquids are stored, shipped, Figure 3 shows a typical cryogenic A liquid transfer line is used to safely and handled in several types of con- liquid cylinder. Cryogenic liquid cylin- remove liquid product from dewars tainers, depending on the quantity ders are insulated, vacuum-jacketed, or cryogenic liquid cylinders. A typical required by the user. The types of con- pressure vessels. They come equipped transfer line for dewars is connected tainers in use are the dewar, cryogenic with safety relief valves and rupture to a bayonet that provides a means of liquid cylinder, and cryogenic storage disks to protect the cylinders from using product vapor pressure buildup tank. Storage quantities vary from a excessive pressure buildup. These or an external pressure source to few liters to many thousands of gal- containers operate at pressures up to remove the liquid. For cryogenic liquid lons. Since heat leak is always present, 350 psig and have capacities between cylinders, the transfer line is connect- vaporization takes place continuously. 80 and 450 liters of liquid. ed to the cylinder liquid withdrawal Rates of vaporization vary, depending valve. Product may be withdrawn as a gas on design of the container, ambient by passing liquid through an internal Liquid product is typically removed conditions, and the volume of stored vaporizer or as a liquid under its own through insulated withdrawal lines product. vapor pressure. For more details on to minimize the vaporization of liquid Containers are designed and manu- the construction and operation of product to gas. Insulated flexible or factured according to the applicable cryogenic liquid cylinders, consult rigid lines are used to withdraw prod- codes and specifications for the tem- Air Products’ Safetygram #27, uct from storage tanks. Connections peratures and pressures involved. “Cryogenic Liquid Containers.” on the lines and tanks vary by manufacturer. Cryogenic storage tanks Dewars A typical customer installation (see Liquid cylinders designed to dispense Figure 2 illustrates a typical vacuum- Figure 4) includes a tank, vaporizer, gases have valves equipped with jacketed dewar. A loose-fitting dust and pressure control manifold. Tanks standard Compressed Gas Association cap over the outlet of the neck tubes may be spherical or cylindrical in (CGA) outlets. Suitable pressure regu- prevents atmospheric moisture from shape. They are mounted in fixed lating equipment may be attached. plugging the neck and allows gas locations as stationary vessels or on Valves provided for the withdrawal of produced from vaporized liquid to railroad car or truck chassis for easy liquid product are also equipped with escape. This type of container is non- transportation. Sizes range from 500 standard CGA outlets, but they are dif- pressurized. The most common unit of gallons to 420,000 gallons. All tanks ferent than the connections used for measure for the capacity of a dewar is are powder- and vacuum-insulated in gaseous withdrawal. This is to prevent the liter. Five- to 200-liter dewars are the annular space. Tanks are equipped accidental introduction of liquid into available. Product may be removed with various circuits to control prod- a gas system, or of gas into a liquid from small dewars by pouring, while uct fill, pressure buildup, pressure system. larger sizes will require a transfer relief, product withdrawal, and tank tube. Cryogenic liquid cylinders, which vacuum. Tanks are designed to ASME are pressurized vessels, are sometimes specifications for the pressures and incorrectly referred to as dewars. temperatures involved.

Figure 2: Typical Dewar

4 Figure 3a: Typical Cryogenic Liquid Cylinder, side view

Liquid Level Gauge Handling Ring Handling Post Annular Space Rupture Disk Inner Vessel Shipment of cryogenic Gas Use Vent Tube liquids Vaporizer (Optional) Compliance with applicable Liquid Tube Outer Vessel Dangerous Goods regulations is Float Assembly required for all shipments by motor freight, rail, air, and water. In the U.S., the Department of Transportation Rubber Shock (DOT) does not regulate certain Mounts cryogenic liquid containers when the Foot Ring pressure does not exceed 25.3 psig (174 kPa). Containers used for trans- porting cryogenic liquids at pres- sures greater than 25.3 psig must be Figure 3b: Typical Cryogenic Liquid Cylinder, top view designed, manufactured, and tested Rupture Disk Pressure Gauge to DOT specifications. International Pressure Gauge Relief Valve Rupture Disk shipments by air must be in compli-

Vent Valve ance with International Air Transport Gas Valve Vent Valve Association/International Civil Air Organization (IATA/ICAO) Dangerous Goods regulations. International ship- ments by water must comply with International Maritime Organization (IMO) regulations. Buildings Liquid Valve Pressure Pressure Liquid Valve Building Building Because of the large expansion ratio of Regulator Valve Economizer Regulator liquid to gas with cryogenic liquids, it is very important to provide adequate ventilation where cryogenic liquids Figure 4: A Typical Customer Station with a Cryogenic Storage Tank are stored and used. Monitors should be available to check for oxygen concentrations in the atmosphere when working with inert cryogens or with liquid oxygen. The minimum permissible oxygen concentration for unprotected personnel is 19.5%, while the maximum is 23.5%. In the case of liquid hydrogen, the atmosphere should be monitored with a flam- mable gas detector. All pressure relief devices should be piped to safe areas, preferably outdoors.

5 Fighting fires 4. When employing water, use large 6. If an inert cryogenic liquid is It is not possible to outline specific fire quantities, preferably in spray form, involved, there is the possibility fighting techniques that will cover all to cool equipment in areas sur- of reducing the oxygen content of types of fires involving cryogenic liq- rounding the fire. Use the spray to the air with the potential risk of uids. Such measures depend upon the cool any burning material below its asphyxiation of the fire fighters. quantity and nature of the cryogenic ignition temperature. If possible, do Judgment should be used to deter- liquid involved, the location of the fire not spray cold areas of equipment, mine which risk is greater to fire with respect to adjacent areas and or direct water onto the cryogenic fighters—that of shutting off the occupants, and on other factors. The liquid. It is very important to keep supply valve, which may be in an following general procedures are ap- water away from vent stacks and area not easily accessible because plicable to all fires involving cryogenic safety relief devices that can be of the fire, or the risk of an oxygen- liquids: plugged with frozen water. Fire deficient atmosphere due to the hoses with adjustable stream-to- reduction of the oxygen content. 1. Everyone not actively engaged in spray nozzles should be available the fighting of the fire should leave where large quantities of flamma- 7. Oxygen, whether gaseous or liquid, the area. If a flammable cryogenic ble cryogenic liquids are handled. is an oxidizer and does not burn, so liquid is involved, the flammable there can be no fire unless com- mixture zone, under unusual at- 5. Depending upon the circum- bustible materials are also present. mospheric conditions, may extend stances, it is generally not advis- The difference is that the presence beyond the normal fog cloud pro- able to extinguish a flammable of additional oxygen will make duced by condensing water vapor cryogenic liquid in a confined area. combustible materials burn much in the air. People should be evacu- If the flammable gas supply cannot faster and more violently or explo- ated well outside the fog area. be shut off, the continued escape sively. Shut off the oxygen supply of unburned gas can create an if at all possible. Neither liquid nor 2. The best fire-fighting technique explosive mixture in the air. The gaseous oxygen can be effectively is simply to shut off the flow of mixture may be reignited by other blanketed by agents such as carbon cryogenic liquid or vaporized gas burning material or hot surfaces. dioxide, dry chemical, or foam. It if a flammable cryogenic liquid is It is usually better to allow the gas is necessary to cool combustible involved. to burn itself out in a confined area materials below their ignition tem- and keep adjacent objects cool with peratures to stop the fire. Use large 3. If electrical equipment is involved water, rather than to risk a poten- quantities of water in spray form. in the fire, be sure the power supply tial explosion. is disconnected before fighting the fire with water. Or use carbon diox- ide or dry chemical extinguishers.

6 First aid For skin contact, remove any cloth- ing that may restrict circulation to the frozen area. Do not rub frozen parts; tissue damage may result. As soon as practical, place the affected area in a warm water bath which has a temperature that does not exceed 105°F (40°C). Never use dry heat. Call a physician as soon as possible.

Frozen tissue is usually pain-free and appears waxy with a possible yellow color. It will become swollen, painful, and prone to infection when thawed. If the frozen part of the body has been thawed, cover the area with a dry, sterile dressing with a large, bulky protective covering, pending medical care.

In case of massive exposure, remove the victim’s clothing while showering him or her with warm water. Call a physician immediately.

If the eyes are exposed to the extreme cold of the liquid or vapors, immedi- ately warm the frostbite area with warm water not exceeding 105°F (40°C) and seek medical attention.

If the body temperature is depressed, the person must be warmed gradually. Shock may occur during the correction of hypothermia. Cardiac dysrhythmias may be associated with severe hypothermia.

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