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ESH Manual Page: 11000: Cryogenic Systems and Radiation Safety

It is SURF's policy to protect the health & safety of persons.  Because persons exposed to reduced oxygen atmospheres at the facility may experience reduced abilities, unconsciousness, or death caused by an unintended release of a compressed and/or liquefied gas it is the SURF policy to:

  • assess the potential for a possible oxygen deficient environment
  • develop control measures, providing equipment to monitor, reduce or eliminate oxygen deficient hazards
  • consider additional requirements in underground spaces.

This policy applies where any release of a compressed and/or liquefied gas may occur.  Emergency response and confined spaces are covered by separate policies.


3.1. Science Director ? must ensure that the requirements of this policy and procedure are implemented for all research projects proposed at Sanford Laboratory.  This includes ensuring qualified persons to review and maintain documentation for ODH risk assessments, and maintain records of reliability of ODH-associated equipment.  

3.2. EHS Department ? is responsible for the purchase and maintenance of personal oxygen monitors, provide training related to ODH issues, provide standardized warning signs,  and maintain records of incidents which have resulted in an oxygen deficient atmosphere. 

3.3. Cryogen Safety Subcommittee ? Consults and makes recommendations on ODH issues.

3.4. Engineering Department- Oversees the design, installation and maintenance of facility ODH associated equipment. 


In-Place Oxygen Monitor ? A device usually permanently attached to a structure, which monitors the concentration of oxygen and alarms at a set value.  In-place oxygen monitors must alarm at 19.5% oxygen and lower and trigger a facility-wide alarm at <18% oxygen.

ODH Classification: ODH classes are based upon the likelihood a fatality could occur and is determined by a risk assessment.  The ODH class determines the required control measures.

Oxygen Concentration ? The molar fraction of a gaseous mixture represented by oxygen.  For a mixture of ideal gases, it is also equal to the ratio of the partial pressure of oxygen to the total mixture pressure.  The oxygen concentration in normal ambient atmosphere is 20.9% (~21%).

Oxygen Deficiency ? Any condition under which the concentration of atmospheric oxygen is less than 19.5% by volume. 

Oxygen Deficiency Hazard (ODH) Operation ? An operation that exposes personnel to an increased risk of fatality in excess of 10-7/hr due to oxygen deficiency.  Unlike confined spaces, ODH work spaces are generally designed for occupancy and provided with normal building type access and egress.  In addition, the hazard is primarily limited to oxygen deficiency which is well understood and controlled through quantitative risk assessment.

Personnel working in ODH space - Any worker employed in an environment with a finite probability of having oxygen concentrations below 19.5 % by volume.

Personal Oxygen Monitor ? A device carried by an individual that monitors the concentration of oxygen and alarms at a set value.  All personal Oxygen Monitors used at Sanford Lab are set to alarm at the mandatory confined space limit of 19.5%.

Self-Contained Self Rescuer (SCSR) ? A device capable of supplying oxygen to be used for an escape during an oxygen deficient event.


5.1. Quantitative Assessments: A quantitative assessment of the increased risk of fatality from exposure to reduced atmospheric oxygen shall be conducted for all operations, which are physically capable of exposing individuals to an oxygen deficiency.  This assessment shall assign an ODH Class to each area with potential risk as well as specify any unusual precautionary requirements.  ODH Class 0 is the least hazardous and is assigned to areas where there is no probability or a very low probability of an oxygen deficiency hazard.  ODH Class 2 is the most hazardous. The classification of an area can change depending on the operations being performed.  If conditions and/or activities change in ways that significantly increase the risk, the associated quantitative assessment must be accordingly revised.  The Fermilab ES&H Manual FESHM 5064 entitled ?Oxygen Deficiency Hazards (ODH)? is used to carry out the assessment.

 5.2.  Underground Assessments: In general, ODH evaluation procedures and measures to address hazards in underground installations are the same as those required for surface installations.  However, time of egress may be longer, gases or cryogenic fluids may accumulate, and rescue operations may be more difficult.  All of these factors must be taken into account in analyses and protective measures. ? If there are oxygen deficiency hazards and normal entry and egress is by means other than by foot, at least one egress path to a ?safe area? which can be reached by foot must be provided.  The safe area must be free of oxygen deficiency hazards and remain so during all plausible equipment failures.  If the safe area relies upon ventilation, emergency power must be provided to its ventilation systems.

  • The path to the safe area must be adequately marked and illuminated and remain free of obstructions during plausible ODH incidents.  Portable light sources may be required in some cases.
  • A written plan for evacuation of personnel from the safe area to the surface must be prepared and approved. 

5.3. Control Measures: Control measures appropriate to the ODH Class shall be implemented as noted in the table below. ODH Class 0 requires no control measures.    

ODH Hazard Class 0 1 2
Facility Environment Controls
1. Warning Signs   X X
2. Ventilation ( minimum requirements established)   X X
3. In-place oxygen monitors   X X
Personnel working with cryogen in ODH spaces
4. ODH training   X X
5. Personal oxygen monitor   X X
6. Self-contained Self-rescuer available   X X
7. Multiple Personnel in Communication     X
8. Medically Qualified     X

 5.4. Equipment Engineering: Equipment at Sanford Laboratory shall be designed and installed to ensure that areas intended for human entry during normal operation will be ODH Class 0, ODH Class 1, or ODH Class 2.  No area intended for human entry during normal operation will be engineered for an ODH Class higher than 2.

 5.5. Occupancy: Occupancy of areas with oxygen deficiency hazards should be limited to the extent practical while still allowing work to be performed expeditiously.  Work in such areas should be planned to minimize the duration of occupancy.  Offices should not normally be located in areas with oxygen deficiency hazards. 

5.6. Records: Records of reliability of ODH-associated equipment and records of ODH alarms that were the result of an oxygen deficient atmosphere shall be maintained. 

5.7. Response to Indication of Oxygen Deficiency (refer to the Emergency Response Plan)

 Indications of a possible oxygen deficiency include:

  • Observations of uncontained cryogens or gases such as vapor clouds, sound of gas leaks, etc.
  • Readings or alarms of gas monitoring devices that continuously monitor oxygen concentrations.

 There are two types of oxygen deficiency monitors 

  • In-place oxygen monitors attached to a lab surface (usually wall).  In-place oxygen monitors are set to alarm in the room in which they are situated when the oxygen concentration is below 19.5% (Local Alarm) and set to alarm the facility when the oxygen concentration is below 18.0% (Facility Alarm).
  • Portable (hand-held) gas monitors intended to be carried by persons.  Mobile (hand-held) gas monitors are set to alarm when the oxygen concentration is below 19.5%.

Response to Indication of ODH (refer to the Emergency Response Plan)

  • Indications of uncontained cyrogens or gases:  Address the issue if within your capability and a gas monitor indicates not less than 19.5%.  Otherwise, leave the area, and report the emergency.
  • Local Alarm or Portable (hand-held) gas monitor alarm less than 19.5%:  Leave area then determine if the alarm is valid.
  • Facility Alarm or Portable (hand-held) gas monitor alarm less than 18.0%: Evacuate to a separate air base.  If escaping to a separate air base may not be accomplished in less than 30-seconds, don an SCSR before escaping. Follow the emergency reporting procedure found in the Emergency Response Plan.  

 5.8.    Re-Entry to Exygen Deficient Spaces:

  5.8.1    Oxygen levels less than 18.0% by volume:
Re-entry to portions of SURF with low levels of oxygen when there are no in-   place Oxygen monitors with remote readout requires emergency response team    (ERT) personnel with SCBA equipment.  Training and medical approval are    required for the use of SCBA equipment.
Re-entry to spaces with in-place Oxygen monitors after activation of a facility    alarm due to low oxygen (<18.0% O2) requires ERT personnel augmented by    technical support staff with expertise in laboratory cryogen systems.  After alarm    activation, it may be possible that increased fresh air ventilation or cryogen    evaporation allows O2 levels to climb above 19.5% . If facility O2 sensors have    returned to levels above 19.5% and alarms have been cleared, SCBA equipment is   not required for ERT re-entry but portable gas testers shall be used to monitor    oxygen content.  If facility O2 sensors remain below 19.5%, SCBA equipment is    required per emergency response procedures.  Training and medical approval are    required for the use of SCBA equipment.

 5.8.2    Oxygen levels less than 19.5% but greater than 18.0% by volume:
  a. Re-entry where a lab user has a plausible explanation about why the local alarm   sounded:  User is to provide the explanation to the lab coordinator.  The lab    coordinator is able to verify via the Building Management System (Metasys web    interface) that the O2 sensor is back above 19.5%.  After verification, the science    lab coordinator may provide permission for re-entry with a portable gas tester.
  b. Re-entry where lab spaces have oxygen sensors inside the room with digital    readout for that sensor outside the room:  Re-entry shall be permitted via: 1)    plausible explanation provided to lab coordinator about why the local alarm    sounded and why the situation is now resolved; 2) oxygen levels again greater    than 19.5%.
  c. Re-entry where O2 sensors are reading lower than 19.5% due to a Dewar relief    valve being stuck open in a small space and this situation is visible via window    (e.g. MJD LN Alcove):  Entry to the space may be permitted when ODH     calculations and / or previous experience show that opening the access doors 
  provide sufficient dilution to raise the oxygen to above 19.5% so that the relief    valve may be accessed and repaired.


6.1  Standards

  • ACGIH Threshold Limit Values ? Simple Asphyxiants 

6.2  References

  • Emergency Response Plan