Physics Division

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Reference Material

Policy and Requirements

Methods of Compliance

Operational Requirements



Properties of Liquids


Relief Valve Sizing


Convective Heat Transfer


Relief Vent Pressure Drops


Oxygen Deficiency Hazards

1.1    Physics Division Cryogenic Safety Committee Charter


In keeping with the Physics Division policy to give the highest priority to Environmental, Safety, and Health concerns in its operations, it is the intent of Physics Division management to minimize cryogenic hazards to staff and visitors and to assure adherence to applicable safety codes.  This will be accomplished through the development of operational procedures, the proper training of personnel, the design of equipment, and the establishment of a Cryogenic Safety Committee.

Responsibilities and Functions

  • Develop the Physics Division Cryogenic Safety Manual
    • Define Physics Division Cryogenic Safety Policy and Requirements
    • Establish design criteria
  • Establish the requirements and scope of cryogenic training of Physics employees and provide for training in specific tasks as needed.
  • Review and approve requests for variance from the rules, regulations and procedures set forth in the Physics Division Cryogenic Safety Manual.
  • Review the design and operation of existing and proposed cryogenic systems in the Division for adherence to regulatory requirements.
  • Identify unsafe conditions and/or practices and assist in the development of corrective action plans.
  • Review personnel accidents, near-misses, and recommend preventive measures.
  • Document meetings, inspections, and other cryogenic-safety activities undertaken by the Committee.


The Physics Division Cryogenic Safety Committee shall consist of at least three Physics Division members appointed by the Division Director and a member from the ESH Division.

Members having expertise in cryogenics from other divisions may be appointed at the discretion of the Division Director.

The Divisional Safety Coordinator shall be a member of the Committee.

Ad hoc members will be invited to participate in safety reviews of specific cryogenic equipment or when membership expertise needs to be expanded.

Frequency of Meetings

This Committee will convene at least quarterly in order to fulfill its responsibilities and accomplish the mandates as specified in this Charter.

Amendment of the Charter

The Committee will review the terms of its charter on an annual basis and at other times as needed and make recommendations for change to the Director of the Physics Division.


The Physics Division Cryogenic Safety Committee will report to the Physics Division Director.


The Committee’s membership must be approved by the Physics Division Director.

1.2    Definition and Scope:

         Cryogenic temperatures are defined as those below 120 K (-153C).  The safety criteria established in this document apply to the cryogens in use in the Physics Division, namely liquid helium and nitrogen.  Flammable fluids, such as hydrogen, and reactive liquids, such as oxygen and fluorine, are excluded.  The use of flammable cryogens will require special approval procedures not outlined in this document.

1.3    Overview of Cryogenic Safety Hazards

         The safety hazards associated with the use of cryogenic liquids (Appendix 1) can be categorized as follows:

         1)     Cold contact burns

                  Liquid or low-temperature gas from any of the specified cryogenic substances will produce effects on the skin similar to a burn.

         2)     Asphyxiation

                  Degrees of asphyxia will occur when the oxygen content of the working environment is less than 20.9% by volume.  Effects from oxygen deficiency become noticeable at levels below ~18% and sudden death may occur at ~6% oxygen content by volume.  This decrease in oxygen content can be caused by a failure/leak of the cryogenic vessel or transfer line and subsequent vaporization of the cryogen.

         3)     Explosion - Pressure

                  Heat flux into the cryogen from the environment will vaporize the liquid and potentially cause pressure buildup in cryogenic containment vessels and transfer lines.  Adequate pressure relief must be provided to all parts of a system to permit this routine outgassing and prevent explosion.

         4)     Explosion - Chemical

                  Cryogenic fluids with a boiling point below that of liquid oxygen are able to condense oxygen from the atmosphere.  Repeated replenishment of the system can thereby cause oxygen to accumulate as an unwanted contaminant.  Similar oxygen enrichment may occur where condensed air accumulates on the exterior of cryogenic piping.  Violent reactions, e.g. rapid combustion or explosion, may occur if the materials which make contact with the oxygen are combustible.

1.4    Staff and Administrative Responsibility

         It is the responsibility of the experimenter in charge of an apparatus to ensure that the cryogenic safety hazards are reduced to as low a level as is reasonably achievable.  This will entail (1) a safety analysis and review for all cryogenic facilities, as described in Section 3, (2) cryogenic safety and operational training for relevant personnel, (3) upkeep of appropriate maintenance and inspection schedules and records.

         It is emphasized that it is the responsibility of the experimenter to maintain the system in the original working order, i.e. the condition in which the system was approved for use.  Alterations to the system which impact worker safety must be reported to the Physics Division Safety Coordinator.

         The ultimate responsibility for safety rests with the worker and is best ensured by thorough education and awareness