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Cryogenic Liquids

Overview

The safe handling of cryogenic liquids involves understanding the unique properties of these materials and ensuring that appropriate safety precautions are taken at all times.

Hazards

Cryogenic liquids are typically odorless and colorless when vaporized to the gaseous state. Most of them have no color as a liquid although liquid oxygen is light blue. However, the extremely cold liquid and vapor have a built in warning property as the cold boil off gases condense moisture in the air, creating a highly visible fog. Cryogenic liquids are liquefied gases with temperatures below -73°C (-100° F).

Cryogenic liquids commonly used include:

Liquid Argon

Liquid Helium

Liquid Nitrogen

Liquid Oxygen

The hazards of cryogenics liquids include:

Boiling &. Splashing

Cryogenic liquids can boil or splash when added to a warm container or when inserting warm objects into the liquid.

Tissue damage

Even short contact with a cryogenic liquid can cause tissue damage like a thermal burn. Frozen skin and frostbite and blood clotting are possible with longer exposures.

Contact with frozen containers can cause skin tears & embrittlement. Skin will freeze to frozen materials, embrittle and tear when an individual attempts to pull it away.

Oxygen deficiency/Asphyxiation

All cryogenic liquids have a significant potential for creating an oxygen deficient environment. Because of their large liquid to gas expansion ration, even small quantities of liquefied gas can expand to displace large amounts of oxygen.

One volume of spilled liquid nitrogen will evaporate into approximately 700 volumes of gaseous nitrogen. Liquid nitrogen spilled in a small, poorly ventilated room can quickly cause unconsciousness and death.

Pressure build-up/Explosion

The large volume ration can cause rapid pressure changes in a containment vessel. Cryogens can condense sufficient moisture from air to create an ʻice plugsʼ, blocking the opening. This is why it is critical to contain liquid cryogens in insulated Dewars with pressure relief valves.

Oxygen enrichment

Cryogenic liquids with a boiling point below that of O2 (N & He) have the ability to condense O2 out of the air if exposed to the atmosphere.

Accelerating the combustion effect of liquid oxygen

Oxygen released from liquid O2 can vigorously support combustion. Any substance that burns will burn better in the presence of oxygen such as organic materials or flammable substances (oil, grease, asphalt, kerosene, cloth and tar)

The use of Liquid Hydrogen is a very high fire/explosion risk. Use of liquid hydrogen must be approved by the Director of Environmental, Health and Safety prior to use.

Process / General Requirements

Hazard & Risk Assessment

Due to the many risks associated with cryogenic liquids, an risk assessment will be performed by your HSE representative. This type of risk assessment takes into account all of the associated risks related to cryogen use with a major focus on oxygen-deficiency. To determine necessary controls to limit the risk associated with oxygen-deficiency the size of the room, the total volume of liquid, and a worst-case release scenario will be evaluated.

Hazard & Risk Assessment

Toxic Gas Monitoring

For areas where the volumes in use/stored and where the risk assessment has identified significant risk for an oxygen-deficient environment shall install O2 monitoring & alarms. The interlocking of ventilation systems (upon alarm, max ventilation is activated) is a best practice that can greatly reduce the risk of significant injury.

Transport

Use the buddy system when filling and transporting cryogenic liquids.
Do not "walk," roll, or drag dewars across a floor. Use carts or containers with wheels
Adhere to the procedure Transport of Liquid Nitrogen in the Elevators in service elevators.

Dewars & Piping

Use only equipment, valves and containers designed for the intended product and service pressure and temperature.
The caps of liquid nitrogen dewars are designed to fit snugly to contain the liquid nitrogen, but also allow the periodic venting that will occur to prevent an over-pressurization of the vessel. Do not ever attempt to seal the caps of liquid nitrogen dewars.
All cryogenic systems including piping must be equipped with pressure relief devices to prevent excessive pressure build-up. Pressure reliefs must be directed to a safe location. Do not tamper with pressure relief valves or the settings for the valves.

Filling

Transfer operations involving open cryogenic containers such as dewars must be conducted slowly to minimize boiling and splashing of the cryogenic fluid.
Vessels being filled must not be left unattended.
Never overfill a Dewar

Personal Protective Equipment

PPE IS NOT DESIGNED TO WITHSTAND IMMERSION IN OR PROLONGED CONTACT WITH CRYOGENIC LIQUIDS!
Use appropriate personal protective equipment (PPE) including insulated gloves and eye protection.
Goggles and a face shield shall be worn during any transfer of cryogenic liquid.
Shirt sleeves should be rolled down and buttoned over glove cuffs, or an equivalent protection such as a lab coat, should be worn in order to prevent liquid from spraying or spilling inside the gloves. Trousers without cuffs should be worn.

Use & Handling

Cryogenic work should be performed in an open, well-ventilated area.
Select working materials carefully. Cryogenic temperatures may alter the physical characteristics of many materials.
Use tongs when placing objects into or removing them from cryogenic liquids
When removing cell-line cages from storage use a hook to locate the handle and raise the cage
Do donʼt dispose cryogenics down the drain, this might cause damage to the facilities.

Training

Liquid Nitrogen

Cryogenic Safety Training

Signs & Labels

Cryogen Storage & dispensing areas

Hazard-warning signs to alert people to the presence of cryogenic liquids.

Area restricted to the authorized personnel only.

No-smoking and no flame or spark producing activities areas.

Emergency Preparedness & Response

If medical attention is needed following a skin or eye exposure to a cryogenic liquid, immediately call 911.

All personnel using cyrogenic liquids must also be familiar with first aid procedures for treating frostbite:

01

Do not rub or massage the affected parts of the body.

02

Never use dry heat to treat cryogenic burns.

03

Warm the affected area of the body rapidly by immersion in water not to exceed 105 F, with body heat, or by exposure to warm air. In the event of massive exposure, the emergency shower should be used to warm the body. All clothing must be removed prior to showering. Maintain the affected area of the victim at normal body temperature until medical help arrives.

04

Calm the victim and avoid aggravating injury. People with frostbitten feet should not walk on them.

05

Prevent infection--use a mild soap to clean the affected area. Dressings need not be applied if the skin is intact.

06

If affected, flush eyes with warm water for 15 minutes.

07

If clothing becomes soaked with cryogenic liquid, it should be removed as quickly as possible and the affected area should be flooded with water as above. Where clothing has frozen to the underlying skin, cold water should be poured on the area, but no attempt should be made to remove the clothing until it is completely free.

Spills

01

Minor spill (< 1 liter) - allow liquid to evaporate, ensuring adequate ventilation.

02

Major release (> 1 liter) - shut off all sources of ignition, evacuate area of all personnel and call 911.

03

DO NOT return to the area until it has been declared safe.

Useful Resources

Transport of Liquid Nitrogen in The Elevators