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SAFETY MANUAL   |   CHAPTER 8

Cryogenic Safety

Good practices, biological safety equipment, personal protective equipment, spill control and biowaste disposal procedures.

Home Safety Manual Chapter 8
CHAPTER 8

Cryogenic Safety

Cryogenic liquids are liquefied gases that are maintained at very low temperatures. Since these liquids are extremely cold and can expand to huge volumes of gases, they are safety hazards.

8.1 Cryogenic Safety

Types of Cryogenic Liquids

  1. Inert gases: Inert gases do not react chemically. They do not burn or support combustion. Examples are nitrogen, helium, neon, argon, and krypton.
  2. Flammable gases: Some cryogenic liquids produce gas that can burn in air. The most common examples are hydrogen, methane, and liquefied natural gas.
  3. Oxygen: Many materials considered non-combustible can burn in the presence of liquid oxygen. Organic materials can react explosively with liquid oxygen. Therefore, the hazards and handling precautions of liquid oxygen must be considered separately from those of other cryogenic liquids.
Chemical Safety Fig 8.1A Liquid dewar flasks of different sizes

Chemical Safety Fig 8.1B Laboratory liquid dewar flask
8.2 Cryogenic Safety

Types of Cryogenic Liquid Containers

  1. Cryogenic liquids are stored in thermally insulated containers. These cryogenic liquid containers are designed to withstand rapid and extreme temperature changes.
  2. Liquid dewar flasks: Liquid dewar flasks are non-pressurised, vacuum-jacketed vessels, somewhat like a Thermos bottle. They should have a loose-fitting cap or plug that prevents air and moisture from entering, yet allows excess pressure to vent. Flasks containing helium, hydrogen, and other low-boiling liquids have an outer liquid nitrogen vessel for insulation (Figure 8.1).
  3. Laboratory liquid dewar flasks: Laboratory liquid dewars have wide-mouthed openings and do not have lids or covers. These small containers are primarily used in laboratories for temporary storage.
Chemical Safety Fig 8.2 (Side and Top) Cross-section of liquid cylinders.
  1. Liquid cylinders: Liquid cylinders are pressurised containers specifically designed for cryogenic liquids. This container has valves for filling and dispensing the cryogens and a pressure-relief valve with a frangible (bursting) disk as backup protection. Never remove/disable the safety valves. Without a safety valve, the tank can explode with disastrous consequences (Figure 8.2).
8.3 Cryogenic Safety

Cryogenic Hazards

  1. Extreme cold hazard: Cryogens can affect the skin like a thermal burn. Brief exposures can damage delicate tissues, such as the eyes. Prolonged exposure can damage skin. There may be no pain initially, but the injury causes intense pain once frozen tissue thaws. Unprotected skin can stick to metal that is cooled by cryogens. The skin can then tear when pulled away. Even non-metallic materials are dangerous to touch at low temperatures. Prolonged breathing of extremely cold air may damage the lungs. Always handle cryo-liquids with appropriate PPE (Figure 8.3).
Chemical Safety Fig 8.3 Required PPE for handling cryogenic liquids
  1. Asphyxiation hazard: When cryogens form a gas, it is colder and heavier than the ambient. This cold, heavy gas does not disperse, accumulating near the floor. Even if the gas is nontoxic, it displaces air. When there is not enough air or oxygen, asphyxiation and death can occur. Oxygen deficiency is a serious hazard in enclosed or confined spaces. Small amounts of liquid can evaporate into huge volumes of gas. For example, 1 litre of liquid nitrogen vaporises as 695 litres of nitrogen gas at room temperature (21°C).
  2. Toxic hazards: Some cryogens can cause specific health effects. For example, liquid carbon monoxide can release large quantities of carbon monoxide gas, which can cause death almost immediately. Refer to the MSDS for information about the toxic hazards of a particular cryogen.
  3. Fire hazard: Flammable gases such as hydrogen, methane, liquefied natural gas, and carbon monoxide can burn or explode. Hydrogen is particularly hazardous. It forms flammable mixtures with air over a wide concentration range (4%–75% by volume). It is also very easily ignited.
  4. Oxygen-enriched air: Liquid hydrogen and liquid helium are so cold that they can liquify the air they contact. For example, liquid air can condense on a surface cooled by liquid hydrogen or helium. Nitrogen evaporates more rapidly than oxygen from the liquid air. This action leaves behind a liquid air mixture that gives a high oxygen concentration when evaporated. This oxygen-enriched air now presents the same hazards as oxygen.
  5. Liquid oxygen hazard: Liquid oxygen contains 4000 times more oxygen by volume than normal air. Materials usually considered non-combustible, such as carbon and stainless steel, cast iron, aluminium, zinc, and Teflon (PTFE), may burn in liquid oxygen. Many organic materials can react explosively, especially if a flammable mixture is produced. Clothing splashed or soaked with liquid oxygen can remain highly flammable for hours.
8.4 Cryogenic Safety

First-Aid

  1. When inhalation has occurred, the victim (who may be unconscious) should be taken to a well-ventilated area. Rescuers should not put themselves at risk - a contaminated area should not be entered unless considered safe. Breathing apparatus may be required but should only be used by trained personnel.
  2. quantities of tepid water (40°C) for at least 15 min, and a sterile burn dressing should be applied to protect the injury until the person can be taken to receive hospital treatment. Do not use a direct source of heat, such as a radiator, and give analgesics (e.g., paracetamol, aspirin).
  3. Refer to the MSDS for more information.
8.5 Cryogenic Safety

Storage

  1. Store at room temperature or below 50°C in a well-ventilated place.
  2. Ensure appropriate hazard warning signs are displayed (yellow triangle with exclamation symbol and text: ‘Liquid nitrogen’ should be used when liquid nitrogen is stored in a laboratory).
  3. The Government regulates cryogen storage. Cylinders and tanks must be regularly audited and certified.
  4. Never store or transport cryogenic liquids in non-rated containers.
  5. Never store cryo-liquids above eye level (i.e., above 5 ft).
  6. Suppose a safety valve blows up. Please investigate to find the reason for it.
  7. Never disable, replace, or weld shut a safety valve. As irritating as they might be, they keep us all safe.
8.6 Cryogenic Safety

Transport

  1. Only a trolley or a specialised vehicle designed with an open roof and a boundary will be allowed with dewars. Trolley handler or driver should wear cryogen PPE while transporting Liquid N2 .
  2. All transportable dewar vessels are fitted with wheels and/or undercarriages. A two-wheeled or four-wheeled handling trolley is available for transporting the 25-litre unpressurized storage containers and must be used for transporting these containers.
  3. Filled cryogen dewars may not be transported in closed vehicles. This includes inside passenger cars, minivans, or SUV-type vehicles.
  4. Never transport an open container of a cryogenic liquid.
  5. Before moving cryogen containers, assess the route for possible obstructions and clutter, lifts, uneven floor, kerbs, stairs, etc.
8.7 Cryogenic Safety

Usage

  1. Always use cryo-rated gloves, a face shield, and an apron while handling cryo-liquids. Cryo-liquids should not be handled with open-toed shoes.
  2. Handle cryo-liquids safely. This means the use of both hands to hold the dewar and duct (Figure 8.4).
  3. Use only fitted transfer hoses designed for use with the dewar container. Cracked or damaged insulation on transfer hoses should be replaced. Do not handle transfer hoses with bare hands, as the fitting is not insulated.
  4. Remove all metal jewellery from wrists and hands (a spill/splash could freeze the jewellery to your skin).
  5. Do not hold the container during filling when transferring from a cryogenic cylinder into a secondary container. It should be placed on the floor or a stable stand, so that the transfer hose rests securely inside the neck of the secondary container.
  6. Never fill containers higher than the indicated level.
  7. Cover transfer dewars only with the covers supplied by the manufacturer. Never tightly seal a transfer dewar or other containers containing cryogenic liquids.
  8. Tongs must be used to withdraw objects immersed in liquid nitrogen.
Chemical Safety Fig 8.4 The correct usage with PPE and use of both hands to hold the tank and tube
8.8 Cryogenic Safety

Cryogenic Spill

  1. Alert others in the area. Evacuate non-essential personnel.
  2. Close the lab doors.
  3. Don appropriate cryogenic PPE before initiating cleanup.
  4. Mark and restrict access to the spill area until resolved.
  5. Use commercial spill kits, designed for cryogens.
  6. Prevent the spread of cryogen vapours and allow safe evaporation.
  7. Ensure the area is well-ventilated to prevent asphyxiation or oxygen enrichment.
  8. Dispose contaminated absorbents (oxygen-enriched) in approved containers after complete evaporation.
  9. Record all incidents for compliance and safety improvement.
8.8 Cryogenic Safety

8.8.1 Cryogenic Spill Kit Contents

  1. Cryogen-rated insulated gloves (loose-fitting, non-absorbent).
  2. Face shield, safety goggles, cryo-apron, and closed shoes (no sandals).
  3. Absorbent pads or spill pillows (for liquid oxygen and hydrocarbon cryogens only – not for LN2 or LHe, where evaporation is the method).
  4. Tongs/forceps are used to handle frozen or broken objects.
  5. Warning signs: “CRYOGENIC SPILL – DO NOT ENTER.”
  6. Oxygen monitor (portable).
  7. Incident report forms.
  8. Minor Spill
    • Applies when spill volume is <1 L. The spill should be confined to benchtop/floor.
    • For inert cryogens (e.g. LN2, LHe, Ar), allow liquid to evaporate naturally in a well-ventilated area. Do not attempt to absorb or mop.
    • For liquid oxygen or flammable cryogens (H2, LNG), keep all ignition sources away. Cover small spills with compatible absorbent material. Allow safe evaporation under supervision.
  9. Major Spill
    • Applies when spill volume >1 L. Or the release is uncontrolled.
    • Do not re-enter until oxygen levels are verified with an O2 monitor and vapours have fully dissipated.
    • Only trained emergency personnel with appropriate PPE may re-enter for inspection or cleanup.
    • For LOX or flammable cryogens, fire services must be notified.
  10. Equipment Spill
    • If the dewar or cylinder is leaking, do not attempt to stop the leak manually.
    • Notify the gas supplier/service contractor for safe removal.
    • If a safety valve is venting, do not block or tamper. Isolate the area and allow venting to complete.
8.8 Cryogenic Safety

8.8.2 Spill on Body/Clothing

  1. Immediately remove contaminated clothing or jewellery.
  2. Flush the affected area with tepid water (40°C) for at least 15 minutes. Do not rub the skin.
  3. For eye exposure, flush at an eyewash station for 15 minutes.
  4. Do not use dry heat or direct radiant heat sources.
  5. Seek immediate medical attention.
  6. Report the incident to PI and OLSEH.
Table 8.1: Health Hazards of Cryogenic Liquids
Hazard Effects Precautions /
Control Measures
Extreme Cold Frostbite, skin burns, tissue damage, eye injury, lung damage if inhaled Wear cryo-rated gloves, face shield, lab coat/apron; avoid direct contact; use tongs for immersion
Asphyxiation Oxygen deficiency leading to dizziness, unconsciousness, or death Ensure good ventilation; oxygen monitors in confined spaces; avoid working alone with cryogens
Toxicity
(specific
gases) 		Gas release (e.g., CO, NO) causing poisoning or immediate death Refer to MSDS; use in well-ventilated areas or a fume hood; leak detection systems
Table 8.2: Handling and Transport Hazards of Cryogenic Liquids
Hazard Effects Precautions /
Control Measures
Pressure
build-up 		Explosion or vessel rupture Never seal cryogen containers; ensure safety valves are functional
Oxygen
enrichment
(LOX,
LH2, LHe) 		Increases the fire/explosion risk of normally non-flammable materials Keep away from flammable/organic materials; avoid contamination of clothing/materials
Fire/
Explosion
(flammable
gases) 		Hydrogen/methane vapours ignite easily over a wide range Eliminate ignition sources; use proper gas detectors; store away from oxidisers
Improper
storage
height 		Spillage or splash injury Store below eye level (<5 ft); use secure stands/trolleys
Inappropriate
transport 		Spill, explosion, suffocation risk in a closed vehicle Use cryogen-rated trolleys; never transport in passenger vehicles; pre-check transport route
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Author: OLSEH Team
Last Updated on: 01 October 2026

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