Before beginning any work with cryogens or cryogen systems, workers must be familiar with the cryogenic equipment and systems they will be using.

Cryogenic liquids users should identify the cryogen equipment and systems to be used, e.g., low pressure storage dewars, open dewar flasks, cryogen cooled vacuum traps, dry/vapor shippers, cryogen filling stations, etc. before beginning any work. Procedural information regarding the use of such equipment should be recorded using a Job Hazard Analysis form to evaluate hazards and provide step-by-step instructions for cryogen use. The cryogenic liquids user should read all manufacturer’s instructions regarding the use of and controls for commercially obtained cryogen equipment and make available this information to all workers. For some cryogen systems, On-the-Job Training (OJT) may be required. It is highly recommended that this OJT requirement be documented by the PI, laboratory/shop/research space supervisors, or department supervisors.

Before work with cryogenic liquids is undertaken, an oxygen-deficiency risk assessment must be conducted. A qualitative risk assessment is easy to use but limited to simple cases.

An oxygen-deficiency risk assessment will address the risk of asphyxiation as well as risks from contact with the cryogenic liquid. Any reasonably foreseeable accidents (i.e., spillage, ice plug, cold burns, etc.) should be considered and appropriate contingency plans implemented to deal with such emergencies

Results of the risk assessment will be used to define cryogen controls. For risk assessments that result in a high chance of oxygen deficiency, additional EHS review will be required.

The main hazard associated with working with dewar flasks is burns from cryogen spills or cryogen-cooled tools. Performing any work with open dewar flasks requires the use of safety glasses with side shields, cryogen gloves, long pants and closed toe shoes, and a lab coat or long sleeves. A lab coat is recommended as the safer option. The following are good laboratory practices for working with open containers of cryogenic liquid:

• When pouring cryogenic liquid from one container to another, never pour above shoulder height.
• Wear cryogen gloves when dipping or inserting samples or equipment into cryogenic liquids.
• Select tools with insulated handles to reduce the risk of burns.
• When submerging a tool or sample into a cryogenic liquid, move slowly – the cryogen can boil violently and splash.
• Keep the area free of clutter to reduce the risk of knocking over a dewar flask and spilling the cryogen.
• Keep all dewar flasks loosely covered when not in use to prevent oxygen enrichment. Use the cover that came with the flask, if one was provided.

Cryogenic Liquid Transport in Elevators
The transportation of cryogenic liquids in elevators poses a potential asphyxiation and fire/explosion risk if workers become trapped in an elevator with a container of cryogen. Passengers must not ride in an elevator with a cryogenic liquid cylinder or dewar under any circumstances.

Cryogen Transport in Vehicles
Self-transport of cryogen liquids by vehicle is not allowed on Rensselaer’s campus. Vendors such as Praxair, Airgas, and Nobel Gas are responsible for the safe delivery and transportation of large cryogen dewars to Rensselaer users.

Cryogenic Materials Transport Between and Within Buildings
Small quantities of liquid nitrogen or liquid argon may be transported in and around buildings in an appropriate low pressure dewar (fitted with a lid) by their carrying handles.

• Do not transport cryogenic liquids in open dewar flasks.
• Do not attempt to carry additional items with the dewar, such as books, beverages, samples or tools.

Larger low pressure dewars may come with casters/wheels attached to the bottom, or the dewar may need to be secured to an appropriate dolly or cart.

• Dollies and carts used to transport dewars should keep the dewar as low to the ground as possible.
• Do not transport low pressure dewars on the top shelf of a hand cart.

Check the entire route ahead of time to ensure that it is free of obstructions and obstacles which may cause a cart to tip.

Heavy cryogenic liquid cylinders must be transported with an appropriate cart designed for the specific cylinder model. 

• Never roll cryogenic liquid cylinders.
• Often, the vendor will deliver the cryogenic liquid cylinder directly to its permanent location and pick it up from there as well – this is the ideal case.

Appropriate PPE is still required when transporting cryogenic liquids around buildings.

Before transporting cryogenic liquid cylinders, the user must ensure that all process valves (gas supply, liquid supply, pressure builder, and vent) are closed.

This section is intended for guidance only and is not a substitute for on-the-job training. Each filling station is different, and on-the-job training is required for each individual fill station. Authorization to use one fill station does not authorize a user to operate other fill stations.

Before undertaking any filling operation, the user must know the following information:

• The appropriate points of contact for the fill-station operation.
• Any applicable personal protection equipment.
• The building point-of-contact for bulk ordering of liquid nitrogen/argon/helium.
• The EHS point-of-contact for notification of events, such as accidental releases.

Room Ventilation
Cryogenic liquids must be stored in well-ventilated areas, such as a lab with an active fume hood or a room with a minimum of six air exchanges per hour. Containers should be stored away from air intakes, high traffic areas and floor drains.

Pressure Relief Valve (PRV) Requirements
Pressure relief valves, or PRVs, used on cryogenic liquid systems must be compatible with cryogenic temperatures and with the physical and chemical properties of the cryogen they are intended to vent. Most importantly, pressure relief valves must not cease to function in extreme cold temperatures or be subject to failure from ice buildup and must have the flow capacity to safely vent excess gas without further buildup of pressure inside the system.

Cryogen Signs
Entrances to labs that use cryogens must be posted with cautionary signs labeled with the cryogen icon. Cryogen bulk filling stations must post a sign with a minimum of the following information:

• Personal Protective Equipment is Mandatory for use of the Filling Station

Personal Protective Equipment

• Face shield over safety glasses
• Cryogen gloves
• Long cuffless trousers
• Closed toe shoes
• Long sleeves or laboratory coat

Training
Cryogenic liquids users must complete the online training, Laboratory Safety Series, through Percipio. On-the-job training on laboratory specific procedures for safe operations from PI, laboratory/shop/research space supervisors, or department supervisors is required before beginning operations involving cryogens.