Chapter 29
Safe Handling of Cryogenic Liquids

Contents

Approved by Joe Dionne
Revised 08/12

NOTE:
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29.1 Policy

This policy describes the safe handling requirements for persons who work with cryogens or operate cryogenic-liquid-handling systems at Lawrence Berkeley National Laboratory (LBNL).

Cryogenic liquids include, but are not limited to, liquid nitrogen, liquid helium, and liquid argon.

29.2 Scope and Applicability

This document addresses cryogenic safety with a primary focus on and specific examples of the inert cryogenic liquids of liquid nitrogen, liquid helium, or liquid argon.

NOTE: Liquid nitrogen is the most frequently used cryogen at LBNL.

All LBNL employees, visitors, affiliates, and subcontractors who handle cryogens or operate cryogenic-liquid-handling systems at LBNL must follow these guidelines:

A thorough evaluation of the safety of a cryogenic application may require a joint effort involving the Environment, Health & Safety (EH&S) Division (Safety Engineering and the Industrial Hygiene Group) and the Facilities Division (Transportation and Rigging Groups).

29.3 Roles and Responsibilities

Role

Responsibility

Facilities Division

 

  • Oversees the Laboratory’s bulk cryogenic systems and their safe design, operation, and maintenance.
  • Must verify that:
  • All  cryogenic-liquid bulk systems are constructed of compatible materials and designed according to the requirements of PUB-3000, Chapter 7, Pressure Safety and Cryogenics, and other applicable industry standard requirements
  • Preventive Maintenance is conducted on all bulk systems in accordance with manufacturers’ specifications.
  • Bulk Systems are promptly repaired  to assure both the safety of the bulk system and ongoing cryogen supply for lab personnel
  • Ensures that no Laboratory personnel other than Facilities employees authorize orperform maintenance or modification on Facilities-owned bulk systems or to the Facilities-owned portion of a system.
  • For assistance with cryogenic system repairs, maintenance, and modifications, contact Facilities Divison’s Mike Botello at (510) 486-7941 or MLBotello@lbl.gov.

Industrial Hygiene SME

  • Is responsible for development, approval, revision and administration of this policy and its implementing documents.
  • Forward suggestions for improvement to Joe Dionne at (510) 486-7586, JEDionne@lbl.gov.

Line Managers

 

  • Ensure that persons within their areas of responsibility comply with this policy and its implementing documents.
  • Must verify  that:
  • LBNL staff and affiliates use only equipment intended for cryogenic service during activities involving cryogens.
  • Commercial equipment is not modified in a fashion that could undermine the designed safety features of the equipment or otherwise create an unforeseen hazard, such as inadequate venting of cryogen spaces.
  • All vessel or piping systems containing cryogenic liquids must have adequate pressure relief. Piping and connections for pressurized cryogenic-liquid handling systems are constructed of safe materials and maintained in leak-free, good condition, including dewars, flex lines, tubing, valves, fittings, brazed joints, transfer equipment, and pressure-relief valves. Failures involving these components could result in exposure of personnel to pressurized sprays of the cryogenic liquid.
  • Pressure relief is provided for any piping segment that has the potential to trap cryogenic liquids (i.e., cryogenic liquid trapped between closed valves).
  • Pressure relief is provided for any sections of a dewar containing cryogenic liquids.
  • Pressure relief is provided in vacuum-insulation spaces to address potential leakage of cryogenic liquids into the vacuum space.
  • Personal Protective Equipment (PPE) is available for workers.

Supervisors and Work Leads

 

  • Ensure that persons within their areas of responsibility comply with this policy and its implementing documents.
  • Ensure that LBNL staff and affiliates complete the required training identified below before performing the indicated work activity or fulfilling the indicated role.

Cryogenic Liquid Users

  • Follow all guidance provided in training and Work Processes to safely use, transport, and dispose of cryogenic liquids.
  • For assistance with cryogenic-liquid applications-including safety engineering, industrial hygiene-LBNL staff and affiliates should contact the appropriate Division ES&H and Facilities Team representative. LBNL’s EHS subject matter expert for cryogens, Joe Dionne, can be reached at (510) 486-7586 or JEDionne@lbl.gov.
  • For assistance with cryogenic system repairs, maintenance, and modifications, contact Facilities Divison’s Mike Botello at (510) 486-7941 or MLBotello@lbl.gov.

29.4 Required Work Processes

Work Process A. General Requirements

1. Identifying Hazards Associated with Inert Cryogenic Liquids

The following tables identify the properties of and major hazards associated with the use of inert cryogenic liquids, focusing primarily on liquid nitrogen. The hazard list should not be considered exhaustive.

Table A.1 Physical Properties of Selected Cryogenic Liquids

Cryogen

Temperature @ 1atm °F/(K)

Liquid/gas expansion

Pressure generated from trapped liquid–allowed to warm to room temperature

LOx

- 297 (90.2)

860 to 1

[Not specified]

LAr

- 302 (87.3)

847 to 1

[Not specified]

LN2

- 320 (77.4)

696 to 1

10,230 psig

LH2

- 423 (20.3)

851 to 1

12,500 psig

LHe

- 452 (4.2)

757 to 1

10,950 psig

Table A.2 Cryogenic Hazards

Hazard

Description

Thermal (low temperature)

  • Contact with cryogenic liquid, its boil-off gases, or components cooled to these low temperatures can readily cause frostbite or cryogenic burns.
  • Release of these cryogens into the work area can damage equipment and property (e.g., frozen water pipes, damaged flooring, damaged electrical cables and their insulation).

Pressurization

  • Cryogenic fluids confined and allowed to warm can generate very high pressures. LN2 confined and allowed to warm to room temperature will generate a nominal pressure of 10,200 psig. The pressure similarly generated by LHe is 11,000 psig. Other cryogens behave in similar fashion. Dry ice (CO2) can generate hundreds of psig pressure if confined. 
  • See Work Process G for an example of valve sequencing instructions for an LN2 fill station. This process illustrates the potential for rupture of piping or vessels if appropriate venting and pressure relief is not provided.
  • The function of vent lines can be defeated by the formation of ice (from condensed moisture) in the vent line. With LHe, air or other gases can solidify to form this blockage.
  • If a cryogenic fluid is subjected to a large amount of heat input, a flash vaporization can occur. This will result in a rapid pressure rise that can be described as a BLEVE (boiling liquid expanding vapor explosion).

Venting

Required vents and pressure-relief devices must be vented to a safe location, which is determined with the following criteria:

  • The specific cryogen in question
  • The volume and flow rates of the potential releases
  • The potential hazards presented by accumulation of the gases or liquids being vented

Oxygen deficiency/asphyxiation

Cryogenic fluids have large liquid-to-gas expansion ratios:

  • LN2 is approximately 680 to 1, (based on volume)
  • LHe is approximately 740 to 1
  • LAr is approximately 820 to 1

These ratios mean that any accidental release or overflow of these cryogenic liquids will quickly boil into gas and may create an asphyxiation hazard by displacing the oxygen content of the surrounding area.

  • In the case of LN2, the nitrogen gas generated from malfunctioning equipment or spills will be cold and denser than ambient air. Even well-ventilated lab spaces that have pits or other low-lying (or recessed) areas could have the oxygen displaced by this cold, dense N2 gas.
  • Argon or carbon dioxide also present these heavier-than-air hazards.
  • Large-volume sources used in small laboratory spaces or in poorly ventilated areas increase the asphyxiation hazard. Oxygen monitors may be advisable in some applications.

Ice buildup

The temperatures associated with cryogenic liquids can easily condense moisture from the air and cause the formation of ice. This ice can cause components or systems to malfunction (e.g., can plug vent lines and impede valve operation) or can damage piping systems.

  • In the case of LHe, air itself can freeze solid and block vent lines.
  • Building exhaust systems that are accidentally cooled to LN2 temperatures can also be damaged by ice formation or the weight of the accumulated ice and the weight of the LN2 itself.
  • The resultant runoff water when the ice melts can also present a hazard.

Materials concerns

The low temperature of cryogenic liquids will adversely affect the properties of some materials, resulting in system or vessel failure. The process for selecting materials to construct vessels and piping systems for cryogen handling must consider the behavior of the materials at cryogenic temperatures.

  • Carbon steels and other metals can become brittle and fracture easily at cryogenic temperatures.
  • Common acceptable materials for construction include metals such as the 300 series stainless steels, some aluminum alloys, and copper or brass.
  • Plastics, such as Tygon® tubing, become brittle and can easily fail in cryogenic applications.
  • Be sure to consult the appropriate references when selecting materials for cryogenic applications. 

Even when the appropriate materials are selected, thermal stresses can lead to failure in some applications. Thermal gradients across a material or piping system or the rapid cool-down of a vessel can generate thermal stresses. Joining materials with dissimilar coefficients of expansion can also generate thermal stresses.

Oxygen enrichment

LN2 is cold enough to condense the surrounding air into a liquid form. The concentration of O2 in this condensed air is enhanced. This condensed “liquid air” can be observed dripping from the outer surfaces of uninsulated/nonvacuum-jacketed lines carrying LN2. This “liquid air” will be composed of approximately 50% O2 and will amplify any combustion/flammable hazards in the surrounding areas.

  • Open dewars of LN2 can condense O2 from the air into the LN2 and cause an O2 enrichment of the liquid that can reach levels as high as 80% O2
  • Air should be prevented from condensing into LN2 with loose-fitting stoppers or covers that allow for the venting of LN2 boil-off gas.
  • Large quantities of LN2 spilled onto oily surfaces (such as asphalt) could condense enough O2 to present a combustion hazard.
  • LHe can also condense air into a liquid or even solid with an enriched O2 content.

Lifting, physical

Studies of accident statistics involving cryogenics commonly include back strains or other lifting injuries associated with dewars. Although not specifically cryogenic in nature, this hazard is appropriate to note as a hazard associated with cryogenic applications.

  • Care should be taken when lifting and moving cryogenic dewars.
  • The proper use of carts or hand trucks can help prevent these injuries.
  • Alternately, the use of low-pressure liquid-transfer equipment and procedures can replace lifting and pouring operations.

LN2/ionizing radiation field

Using LN2 in high ionizing radiation fields that can generate ozone or nitrogen oxides may cause a potential explosion hazard when the LN2 condenses quantities of oxygen from the atmosphere. The applicable control measure is to minimize the accumulation of oxygen into the LN2 and to keep containers free of hydrocarbon contamination.

Noise

Transfer or venting of cryogens can generate, in some cases, noise levels that may require hearing protection. Sound levels in excess of 150 dBA have been recorded during routine tank filling. A redesign of the equipment or procedure could also be addressed in these cases.

Other, specific

Other cryogenic fluids present specific hazards in addition to the above concerns. Examples include:

  • LOX, with the added concerns of materials compatibility and cleanliness (hydrocarbon contamination), presents additional enhanced combustion hazards.
  • LH2, with the added concerns of low ignition energy, proper bonding and grounding of equipment, and venting of boil-off gases, presents additional hazards of flammability and materials embrittlement.

This list is not to be considered exhaustive.

Seek additional guidance from the appropriate division ES&H team for a thorough hazard analysis and safe operation of these systems.

2. Potential Accidents with Cyrogenic Hazards

LBNL staff and affiliates must be aware of the possible accident scenarios for the LBNL environment. The following table lists known, common accident scenarios involving LN2 applications.

Table A-3: Potential Accidents

Potential Accident

 Description

Accidental releases (or overflows)

Accidental releases (or overflows) of LN2 can present hazards and cause property damage, as noted in the hazards discussed above.

  • The most frequent cause of accidental releases is inadequate training on specific hazards and procedures.
  • These releases can come from automated level-control systems, but more frequently are the result of manual operations left unattended.
  • The level of concern over these releases increases with the volume of the cryogen source.
  • House liquid nitrogen systems present the potential for release of very large quantities of LN2. Separate (stand-alone) supply dewars are inherently safer in this respect because they have smaller volumes.
  • Releases of LN2 into a building or lab space are the most hazardous, presenting the primary hazards of asphyxiation, personnel exposure, and property damage.

Releases into building exhaust systems

Releases into building exhaust systems also can present significant hazards.

  • These releases typically occur when the operator opens a bypass valve in an attempt to precool the piping to LN2 temperatures and then mistakenly leaves the bypass valve open. See Figure G-2 in Work Process G for a typical house LN2 system configuration.
  • These releases can adversely affect the normal operation of the building’s exhaust system or can cause the exhaust system to fail and release significant quantities of LN2 into the building’s air space.

Pressure buildup (pressure relief valves, PRVs)

Pressure relief valves (PRVs) are required on cryogenic-liquid piping systems to prevent excess pressure buildup when the liquid is trapped between closed valves.

  • Vent PRVs to a safe location (not into the lab or the ceiling plenum) to prevent a hazardous accidental release upon actuation of the valve or on failure of the valve to reseal.
  • The PRV should be rated for thes pecific application. PRVs rated for LN2 are not appropriate for liquid CO2 applications.

Back injuries

Back injuries may result from lifting cryogenic-liquid dewars.

Tipping of dewars

Storage dewars of LN2 or LHe may be accidentally tipped over when crossing obstructions, such as door thresholds.

  • Handle dewars with appropriate care.
  • Ensure floor surfaces are free of obstructions and appropriate for moving dewars.
  • Ensure all parts of the dewar (wheels, handles, etc.) are in proper functioning condition.

Accidents caused by equipment failure (equipment not designed for cryogenic service)

Cryogenic liquids should only be handled in apparatuses specifically designed for that purpose. 

  • Accidents frequently occur when equipment not designed for cryogenic service is used, such as when a consumer-rated Thermos® bottle is used for LN2 or dry ice. Overpressure that ruptures the container is frequently the result.
  • Accidents can also occur when cryogenic-rated equipment is inappropriately modified and the original safe-venting design is compromised.

3. Guidance for Materials of Construction

LBNL staff and affiliates should verify that material and equipment used in cryogenic applications will not become brittle and hazardous at low temperatures.

Material Guidelines

Common acceptable materials include the 300 series stainless steels, aluminum, copper, and brass.

If brittle materials are used, equipment owners should consider mitigating hazards by using shielding or remote testing.

In general, Tygon® tubing, carbon steels, and iron become brittle and fracture easily at cryogenic temperatures and are not suitable for these applications.

Work Process B. Procurement

To obtain cryogens, contact the principal investigator to arrange for:

Work Process C. Oxygen-Deficiency Risk Assessment

Before work with cryogenic liquids is undertaken, an oxygen-deficiency risk assessment must be conducted. An easy to use oxygen-deficiency calculator has been developed as a screening tool. 

Required Inputs for Oxygen-Deficiency Calculator

The room or space dimensions (i.e., length, width, and height)

The cryogen usage (i.e., type and quantity)

 

Assessment Results

Results of the risk assessment will be used to define cryogen controls. See below for additional details on the risk-assessment process for oxygen-deficiency hazards.

Results of qualitative and quantitative risk assessments will be stored in the Hazard Management System database for future reference and for use in establishing Activity Hazard Documents when required.

For Risk Assessments that result in an Oxygen Deficiency Hazard Class of “2” or above, an Activity Hazard Document must be prepared. Based on the professional judgment of the Cryogenic Subject Matter Expert (SME), the Activity Hazard document may include control measures as detailed in Table C-2.

 

1. Requirements

Before work with cryogenic liquids is undertaken, an oxygen-deficiency risk assessment must be conducted.

The ODH assessments will need to 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 taken into account and appropriate contingency plans implemented to deal with such emergencies.

2. Oxygen-Deficiency Risk-Assessment Calculation

The oxygen-deficiency risk assessment will take into account the location of work and room size. LBNL staff and affiliates should be made aware of the increased risk of oxygen depletion in a small room.

Risk Assessment Determinations

Calculate the oxygen concentration in the room that results from the loss of the entire contents of the liquid vessel in a short period of time (i.e., the worst-case scenario).

Include the following:

  • Significant potential sources of reduced oxygen
  • Failure mechanisms
  • Operations (i.e., steady state and start-up, repairs, special operations, and shutdown)
  • Gas dynamics (i.e., ventilation (natural, forced), stratification/mixing, and diffusion)
  • The bases used for the conclusion

For qualitative assessments of the potential to create an oxygen-deficient atmosphere, the simple ODH calculator will be used. (To download the ODH Calculator, go here or click on the image shown below. For more information about the ODH calculator, see An Overview of the ODH Calculator, below.) An example of the actual output simulating the transport of a 160 L liquid nitrogen dewar in an elevator is shown below.

ODH Calculator
calc

If oxygen levels could fall below 18%, suitable control measures should be implemented, e.g., filling or storing vessels in a ventilated room, installing a permanent oxygen monitor, or using smaller storage vessels. An example of a better-ventilated room will generally include a lab with an active fume hood with at least 25% bypass airflow and an active flow-monitor alarm that is set up so the alarm cannot be disabled by local residents.

NOTE: In more complex situations involving multiple dewar or cryogenic systems, a quantitative risk assessment will be conducted.

Examples of acceptable alternatives to oxygen-deficiency risk assessment methodology include, but are not limited to, the Fermi Lab ODH methodology.

Once the ODH fatality rate (f) has been determined, the operation will be assigned an ODH class according to Table C-1 below.

Table C-1. Oxygen-Deficiency Hazard (ODH) Classes

Oxygen-Deficiency Hazard (ODH) Class

Risk [f] (hr-1)

0

<10-7

1

> 10-7 but     <10-5

2

> 10-5 but     <10-3

3

>10-3

Results of qualitative and quantitative risk assessments will be stored in the Hazard Management System database for future reference and for establishing Activity Hazard Documents when required.

3. An Overview of the ODH Calculator

The ODH calculator is a simple tool that allows rapid ODH evaluation of a room using conservative assumptions.

Understanding Oxygen-Deficiency Calculator Results and Limitations

If there is no oxygen deficiency hazard for any routine condition and the ODH hazard class is zero, no further action is required.

If either the ODH hazard is not zero or an oxygen deficiency hazard is possible for any routine operation, the ODH of the room must be analyzed by an industrial hygienist, and further engineering and/or administrative controls may be required.

The ODH calculator is not for use with plumbed liquid nitrogen supplies; the ODH of these locations must be evaluated by other methods. (Contact SME for more information)

If the room has activities that do not map onto the scenarios in the ODH calculator, the ODH must be determined by other methods. (Contact SME for more information)

4. ODH Calculator Model

The ODH calculator uses the Fermilab probabilistic methodology to determine the oxygen deficiency hazard (Fermilab ES&H Manual 5064). For each scenario, the value of %O2 is determined using %O2=0.21*exp(–volume of cryogen/volume of room). The probability of death upon exposure to this concentration of oxygen is calculated using the Fermilab methodology. Finally, the probability of each scenario is multiplied by the probability of death for that scenario, and these products are summed to give an overall probability of death resulting from cryogen use in this room. The ODH class is assigned using the values in Table C-2, below. Although this model uses a formula for the %O2 in the absence of ventilation for the probabilistic model, there is an implicit assumption of one air exchange per hour.

Table C-2. ODH Hazard Classification

ODH Class

Fatalities per hour from model

0

<10-7

1

<10-5 and >10-7

2

<10-3 and >10-5

3

>10-3

5. Scenarios Considered in Model

Routine Operations (all have a probability of 1 per hour)

Possible Scenarios

Scenario

Description

Storage of cryogen

Release of all stored cryogen is assumed to be 5% per day. The reported values are 2% per day for typical storage dewars, but the 5% value is used to account for the fact that some dewars, especially high-pressure storage dewars, cryomagnets, and cryogenically cooled traps, have a larger release rate. All cryogen is assumed to be liquid helium with an expansion ratio of 757, which is slightly conservative compared with that of liquid nitrogen (680). But the liquid helium expansion ratio has the advantage that less data needs to be entered since only cryomagnets, not different types of cryogens, are entered into the model.

Routine work

Work with cryogen that will actively be generating gas includes such tasks as working in open dewars (crystal mounting) or using liquid nitrogen to actively cool experiments (cryostream). All of the cryogen in the dewar is assumed to be used within one hour. Cryogen is assumed to be liquid helium for the sake of expansion ratio.

Filling transfer dewars

A smaller, transfer dewar is filled from a larger, storage dewar. Loss rate is assumed to be 10%.

Refilling cryomagnet

When a cryomagnet has its liquid helium and liquid nitrogen reservoirs refilled, loss rate is assumed to be 10%. Both dewars are assumed to be filled at the same time.

Cool-down of cryomagnet

A cryomagnet is initially cooled with liquid nitrogen then cooled with liquid helium, which may be in separate reservoirs. All operations are assumed to be finished within one hour. The liquid nitrogen loss rate is 20% of the volume of the reservoir, and the liquid helium loss rate is 50% of the volume of the reservoir. Based on cool down of a Quantum Designs Magnetic Property Measurement System on 10/26/09, 76 L of LHe is needed to cool and fill a 56 L reservoir. LN2 loss rate is an estimate and is probably too high since liquid nitrogen has a high heat of vaporization.

Nonroutine scenarios: power outage

The assumption is that power is lost to a building (especially a bio lab containing freezers with liquid nitrogen backup) for 8 hrs before someone notices (this may not be a very plausible scenario). All of the nitrogen evolved from storage dewars and the nitrogen used to cool down the freezers evaporates into the lab. The rate of liquid nitrogen use for freezer backup was obtained from Fisher and So-Low and is 7 lbs/hr and 11.6 lbs/hr for 13 cu ft and 25 cu ft –80 °C freezers, respectively. The assumption is that this event happens every two years, which is grossly conservative; this scenario is not plausible in the absence of an earthquake (p=5.7x10-5/hr).

Transfer dewar spill

Transfer dewar is knocked over and all cryogen evaporates into room. The assumption is that this event happens approximately four times per year (p=4.6x10-4/hr).

Complete failure of dewar

Dewar fails (valve is snapped off) and all cryogen is lost into room and evaporates in an hour. Failure rate is from Fermilab for failure of vacuum jacket of dewars (p=1x10-6/hr). This is in good agreement with our observations of one failure in 10 years among ~10 dewars in the 70/70A complex (p=1.14x10-6/hr). The oxygen level is calculated for the largest dewar that can fail, and the probability is multiplied by the total volume of stored cryogen divided by the volume largest dewar to account for the probability of other dewars failing.

Magnet quench

Cryomagnet ceases to be superconducting and boils off helium equivalent to the stored energy (heat of vaporization 0.0845 kJ/mol). If the stored energy is unknown, all of the helium in the jacket is assumed to be vaporized. Vaporization of liquid nitrogen is not an issue due to its much higher heat of vaporization (5.6 kJ/mol), which means that 66 times less nitrogen would be released than helium. Failure rate is from Fermilab (p=1x10-6/hr).

6. Explanation of Terms to Be Entered into the ODH Calculator

Explanation of Terms

Terms

Description

Building, room, fume hood, room dimensions

Self-explanatory

Total volume of cryogens

Self-explanatory. Includes the volume of all storage dewars plus any other device that contains cryogens, e.g., cryomagnets, freezers, cold traps. Note that all cryogens are assumed to be liquid helium with an expansion factor of 757:1, which is slightly conservative compared with that of liquid nitrogen (694:1) and slightly nonconservative with respect to that of liquid argon (849:1).

Largest storage dewar

Self-explanatory. Largest dewar by volume in the room can be a storage dewar, freezer, cryomagnet, etc.

Largest transfer dewar

Transfer dewar is a smaller dewar that is filled from a storage dewar and is used to transfer cryogen to another location. These are typically 4 L dewars, but larger dewars for cryostats are also to be included here.

Largest volume used routine

Largest volume of cryogen that is used in an open system. This includes open dewars, and dewars used with cryostreams, cryostats, etc.

Number of freezers with LN2 backup

Self-explanatory. If the freezer is smaller than 13 cu ft, include it in the 13 cu ft box. If it is much larger than 25 cu ft, enter the volume of the freezer divided by 25 (this quotient needs to be multiplied by the number of large freezers, of course).

LN2 in cryomagnet

Self-explanatory: the volume of the LN2 jacket, if present.

LHe in cryomagnet

Self-explanatory: the volume of LHe in the cryomagnet dewar.

Energy of cryomagnet

Energy stored in the cryomagnet in kilojoules. If unknown, just enter a zero in this box. The magnet will be assumed to volatize all of the stored LHe in a quench.

Work Process D. Controls and Space Classification

1. Controls for Handling Cryogenic Liquids

Depending on the results of the Oxygen Deficiency Hazard (ODH) risk assessment, a variety of engineering controls may be required to be implemented to safely handle cryogenic liquids. Table D-1 below lists possible engineering controls based on the Oxygen Deficiency Hazard class.

Table D-1. Possible Oxygen Deficiency Hazard Control Measures

Control

Hazard  Class 1

Hazard  Class 2

Warning signs

X

X

Oxygen monitor

X

X

Ventilation

X

X

Medical approval

 

X

ODH training

X

X

Personal oxygen monitor

 

X

Self-rescue respirator

 

X

Communication system

X

X

2. Personal Protective Equipment (PPE) for Handling Cryogenic Liquids

Engineered controls should be the primary means of worker protection. Where engineered controls may not be complete or feasible, workers must wear the appropriate PPE to augment any controls in place.
Certain types of operations may also increase the risk of exposure to cryogenic liquids. Selection of appropriate PPE must include careful consideration of the specific system configuration and the potential for exposure to all potential hazards. Examples of this include:

Many other operations are considered low risk. For example: handling small amounts (<5 L) of liquid nitrogen (LN2) in nonpressurized open containers at atmospheric pressure (e.g., pouring LN2 from a nonpressurized dewar into another open container or cryotrap). In these limited situations, a combination of PPE, engineering controls, and/or administrative controls (e.g., training) can prevent splashed LN2 from becoming trapped against the skin.

Many skin injuries have occurred when cryogen becomes trapped against the body by PPE. This is why cryogen gloves are designed to be loose fitting. They provide users with a way to quickly remove them in cases where a user is splashed with cryogen. For the same reason, webbed shoes (e.g., athletic shoes) or cuffed trousers must not be worn when there is a potential to be splashed with cryogen.
Table D-2 below describes PPE required to be worn by Berkeley Lab staff and affiliates for routine handling of liquid nitrogen.

Table D-2. Summary of PPE Requirements for Cryogen Use

Operation

Potential Hazard

Face Shield and Safety Glasses (with Side Shields)

Safety Glasses (with Side Shields)

Cryogen Gloves

Closed-Toe Shoes

Long Pants (No Cuffs)

Lab Coat or Long-Sleeve Shirt

Remarks

Pouring small nonpressurized (<5 liters) volume of LN2 between open containers

Eye or skin injury from splashing

 

X

Recommended1

 

X

 

X

 

Recommended1

Avoid pouring cryogens from above chest level

Work with experimental samples immersed in LN2 in small (~1 L) dewar

Frostbite and burns from cold surface contact

X

 

Recommended1

 

X

 

X

Recommended1

Thermally insulated hand tools may be an effective alternative to gloves

Handling chilled metal transfer lines

Frostbite and burns from cold surface contact

X

X

 

X

 

X

 

X

Dispensing LN2 from a pressurized line to an open dewar2

Frostbite and burns from cold surface contact, eye and skin injury from splashing

 

X

 

X

 

X

 

X

 

X

 

X

 

Closed pressurized line LN2 or LHe transfer

Frostbite and burns from contact with the unexpected release of pressurized cryogen liquid or gas

 

X

 

X

 

X

 

X

 

X

 

X

1 Recommended. For a few limited operations, cryogen gloves or long-sleeve shirts/lab coats may not be needed.
2 When using a phase separator between the pressurized LN2 line and the open nonpressurized dewar, the risk of a cryogen splash is substantially reduced.

3. Continuous Oxygen-Monitoring Systems

The EH&S Division is developing guidance for the continuous oxygen-monitoring system that will depend on the size, breadth of ODH risk assessment resulting in a “1” or above hazard rating. Once all of the ODH hazard risk assessments are performed, the scope of the program will be known, and EHS will design an appropriately-scaled system that addresses roles/responsibilities, QA, maintenance, calibration, documentation, and configuration control requirements for continuous oxygen-monitoring systems. In the interim, contact Joe Dionne at (510) 486-7586 for guidance.

Contact an Industrial Hygiene representative or Joe Dionne for assistance in determining the need for oxygen monitors.

4. Cryogen Signs

Work Process E. Cryogen Safety Training

LBNL staff and affiliates must complete the required training identified below before performing the indicated work activity or fulfilling the indicated role. Untrained LBNL staff and affiliates may temporarily work under the direct supervision of an appropriately qualified supervisor or work lead if the conditions/limitations of such work are documented (e.g., specific activities and duration) before performing the work.

Requirements for LBNL Staff and Affiliates Handling  Cryogenic Liquids

Complete EHS0170 as required by this chapter

Receive on-the-job training on site-specific procedures for safe operations before beginning operations involving cryogens

Work Process F. Verification of Controls

Depending on the outcome of the hazard assessment, the Cryogens SME may need to verify all designated controls are in place prior to the start of cryogen use.  The Principal Investigator will arrange for the verification if one is indicated as part of the planning and assessment process.

Work Process G. Work Procedures

1. Guidance for Handling Cryogenic-Liquid Equipment: Hazards Associated with Handling Cryogenic-Liquid Equipment

Cryogenic burns can be serious. LBNL staff and affiliates must select the appropriate level(s) of Personal Protective Equipment (PPE) commensurate with their application. Considerations include:

The use of PPE for handling cryogenic liquids is discussed in Work Process D, Step 2, of this chapter. Chapter 19 of the PUB-3000 provides a broad overview of the Laboratory’s PPE policy.

The tables in Work Process A, Step 1, identify properties and the major hazards associated with the use of inert cryogenic liquids, focusing primarily on liquid nitrogen. The hazard list should not be considered exhaustive.

Hazards and activities related to the use of cryogenic liquids include those in Table G-1.

Table G-1. Hazard Concerns

Hazard/Activity

Reference

Asphyxiation

PUB-3000, Chapter 29, Safe Handling of Cryogenic Liquids

Confined spaces

PUB-3000, Chapter 34, Confined Spaces

Pressure

PUB-3000, Chapter 7, Pressure Safety

Skin burns

PUB-3000, Section 4.7, Chemical Hygiene

LBNL staff and affiliates may provide pressure relief by opening vent lines, pressure-relief valves, or burst disks, depending on the application. See Figure G-1 below for an illustration of pressure-relief locations. 

diagram

Figure G-1. Pressure Relief Locations

2. Operational Guidance

During operations involving cryogenics, LBNL staff and affiliates must:

NOTE: Hazardous quantities of cryogenic liquids can be released into lab spaces or into building exhaust systems when manual valves are left unattended. When precooling house LN2 piping lines, consider where the liquid and the resultant boil-off gas is going and at what point it will begin to collect as a liquid and present a hazard. The overflow of cryogenic liquids may present an immediate hazard to personnel and facilities.

Use cryogenic liquids only in well-ventilated areas or with local exhaust ventilation. Cold rooms are poorly ventilated small rooms and must not be used for the storage of liquid nitrogen vessels.

NOTE: Both system design and operational practices should be used to limit accidental releases of cryogenic liquids. Consider the use of small-volume sources (as opposed to large-volume house sources) of cryogenic liquids as a way to limit accidental releases.

3. Transporting Cryogen Dewars

  1. Cryogen Dewar Transport in Elevators

    Guidelines for Elevator Use

    The transportation of cryogenic liquids in elevators represents a potential asphyxiation and fire/explosion risk if workers become trapped in an elevator with a dewar of cryogen.

    People must not ride in an elevator in which large cryogen dewars are being transported.

    When large dewars are transported in an elevator, a clearly visible sign must be used to warn staff and students not to enter the elevator while the dewar is present. After the dewar reaches its destination, the person transporting the dewar will remove the dewar from the elevator and return it to normal service.

  2. Cryogen Transport in Vehicles

    Guidelines for Vehicle Use

    Under no circumstances is a cryogenic dewar to be stored or transported in the cabin or trunk of a vehicle.

    Only dry shippers can be used to transport cryogenically frozen sample in vehicles. Dry shippers are specially designed transportation dewars that can be safely used for transporting frozen samples. Dry Shippers contain a small volume of liquid nitrogen that is contained within an absorbent. Examples of dry shippers designed for shipment can be found at the following link.


    Vendors such as Praxair, Airgas, and Matheson Tri-Gas are responsible for the safe delivery and transportation of large cryogen dewars to LBNL users.
  3. Cryogen Transport between and within Buildings

    Small quantities of liquid nitrogen may be transported around buildings in an appropriate dewar.

    Note: Consumer products such as Thermos® bottles are not approved for cryogenic applications. Although the container itself may hold cryogenic liquid in an adequate manner, the lid, even when loosely applied, does not allow for proper venting of boil-off gases.

    Guidelines for Transport between Buildings

    In most situations, large dewars (i.e., greater than 5 liters) with wheels can safely be moved from the cryogen filling station to the lab. If the large dewar does not have its own wheels, the dewar must be secured to an appropriate dolly and transported to the use area.

    Ensure that the route to be taken is free of obstructions.

    Wear appropriate PPE when transporting cryogens around buildings.

    At the conclusion of operations, LBNL staff and affiliates must verify that appropriate valves are shut off.


    In the event of an emergency, LBNL staff and affiliates must:

    • Evacuate and not enter the area when oxygen monitors indicate a lack of oxygen.
    • Notify personnel in surrounding areas who may be affected.
    • Seek medical attention for any injuries or cryogenic burns.
    • Report the event to their work lead, supervisor or the LBNL emergency number (510) 486-7911 or 911.
    • For off-site locations (e.g., Potter, JBEI, JGI, etc.), use the local emergency number.

4. Operating a LN2 Fill Station

This section applies to house-supplied, liquid-nitrogen fill stations located within laboratory spaces and is intended for guidance only. Specific system procedures should always be reviewed by persons who are knowledgeable about the installation.

Before undertaking a dewar-filling operation, know the following information:

Table G-2. Dewar-Filling Process

Step

Action

PREPARATION FOR USE

1

Check that the oxygen monitor (if applicable) is operational.

2

Locate flex lines and fill valve away from point of discharge.

3

Make any connections for fill or vent that are required.

4

Position the dewar for filling.

5

Put on personal protective equipment (PPE). Wearing safety glasses is required for the open handling of LN2. Additional PPE, such as face shield and gloves, may also be required. PPE requirements depend on the specific system design and operation.

USE

Caution: Safe use of this system requires 100% manned operation. Operators should not leave the area with a valve either in the open or partially open position.

6

When necessary, precool the LN2 line by opening the bypass valve and allowing flow until the supply line is adequately precooled. This may be evidenced by frost on the valve or piping and components. Do not leave the area during line precool. The line is precooled in an effort to minimize the quantity of nitrogen gas that will be vented into the laboratory air space during the filling process.

figure

Figure G-2. Example of LBNL House LN2 Supply Piping

7

Close the bypass valve at this time. The line should be adequately precooled so that when the fill valve is opened, liquid-phase nitrogen (or a minimum of gas phase) will flow.

8

Slowly open the fill valve. You should be able to hear the LN2 flowing through the line and into the dewar. Do not leave the area during the dewar-fill operation.

SHUTDOWN

9

When the dewar is full, close the fill valve and ensure that both valves are in the fully closed position (90 degrees from the line orientation).

10

Vent off any residual pressure, then disconnect any connections made and remove the dewar from the fill station.

 

5. Calculations for Oxygen Deficiency When Filling LN2 Dewars

The intent of this work process is to provide a quick way of assessing the potential for creating an oxygen deficient environment when using cryogens in indoor settings. Normal air contains nominally 20.9% oxygen. Cryogen, when released indoors in nonventilated rooms, has the potential of displacing oxygen, and thereby creating an oxygen deficient atmosphere (i.e., less than 18% oxygen by volume).

  1. Calculation of Oxygen Depletion Due to Liquid Nitrogen Losses

    Four cases are considered here:

    1. Normal evaporative losses
    2. Filling losses
    3. Spillage of the vessel's contents
    4. Loss of the entire contents of the vessel immediately after filling

    The British Compressed Gases Association (BCGA) recommends that, for the purpose of risk assessment, the worst case possibility (iv) is considered.

    OXYGEN CONCENTRATION CALCULATION

    The oxygen concentration, Coxygen in a room may be calculated using the formula:

    Coxygen = 100 x Voxygen / Vroom

    Where:

    Voxygen is calculated as in (ii), (iii), or (iv) below
    Vroom is the room volume in M3

  2. Normal evaporative losses

    Over sufficiently long periods, the percentage decrease in oxygen concentration due to normal evaporation losses from a vessel is approximately:

    0.21 x 100 x Ct

    Where:

    0.21 represents the normal concentration of oxygen in air (21%)
    Ct = L ÷ (Vroom x N)

    Ct is the increase in nitrogen concentration
    L is the gas evaporation rate in M3 h-1
    N is the number of air changes per hour

    Manufacturers quote evaporation losses for their vessels (normally as a volume of liquid nitrogen lost per day).

    Allowance should be made, by doubling these figures, for the deterioration of insulation performance over the lifetime of the vessel:

    L = 2 x 700 x liquid nitrogen loss in liters per day ÷ (24 x 1000)

    Where:

    2 allows for the deterioration of insulation

    700 represents the gas factor for nitrogen (1 liter of liquid nitrogen produces about 700 liters of gas)

    EXAMPLE

    For example, a basement room 4x3x3 m (36 M3) contains five 10-liter dewars, whose evaporative losses are quoted by the manufacturer as 0.15 liter liquid nitrogen per day per dewar. A basement room has about 0.4 air changes per hour:

    L = (2 x 700 x 5 x 0.15) ÷ 24 x 1000 = 0.044 M3 h-1
    Ct = 0.044 ÷ (36 x 0.4) = 0.003 and the oxygen depletion is 0.06%.

    In this case, the normal evaporation losses have an insignificant effect on the oxygen content of the room. However, where Ct = 0.07 or higher, the oxygen depletion becomes 1.5% or more, and extra ventilation and/or oxygen monitoring will be required.

  3. Filling losses

    When a vessel is filled, some loss always occurs as it is cooled to liquid-nitrogen temperature. The BCGA recommends that a loss of 10% of the vessel's capacity should be assumed in order to assess the risk from filling losses:

    Voxygen (M3) = 0.21 [Vroom - (0.1 x Vvessel x 700 x 10-3)]

    Where:

    0.21 represents the normal concentration of oxygen in air (21%)
    0.1 represents the loss of 10% of the vessel's capacity
    Vvessel is the vessel's capacity in liters
    700 represents the gas factor for nitrogen (1 liter of liquid nitrogen produces about 700 liters of gas)

    EXAMPLE

    With the same room and dewars as in (i):

    Voxygen = 0.21 [36 - (0.1 x 10 x 700 x 10-3)] = 7.413 M3
    Coxygen = 100 x Voxygen / Vroom

    Once again, there is no significant effect on oxygen concentration in normal use.

  4. Spillage

    For the spillage of the entire contents of a vessel:

    Voxygen (M3) = 0.21 [Vroom - (Vvessel x 700 x 10-3)]

    EXAMPLE

    If the entire contents of a 10-liter dewar were spilled in this 36 M3 room, then:

    Voxygen = 0.21 [36 - (10 x 700 x 10-3)] = 6.09 M3
    Coxygen = 100 x Voxygen / Vroom = 16.9 %

    This spillage would significantly deplete the oxygen concentration.

  5. Filling of a vessel followed by the spillage of its entire contents

    Voxygen (M3) = 0.21 [Vroom - (1.1 x Vvessel x 700 x 10-3)]

    Where 1.1 represents 10% filling loss + 100% loss of the vessel's contents by spillage

    This is the worst case that should be considered in the risk assessment—both (ii) and (iii) are taken into account:

    Voxygen = 0.21 [36 - (1.1 x 10 x 700 x 10-3)] = 5.943 M3
    Coxygen = 100 x Voxygen / Vroom = 16.5%

    If the risk assessment shows that alternative storage arrangements must be considered or oxygen monitoring must be installed. Alternative arrangements may include:

    • Positioning the vessels elsewhere
    • Using smaller vessels
    • Arranging for any pressure-relief devices to vent to a safe place outside of the room
    • Installing mechanical ventilation possibly linked to the low-oxygen alarm
    • Requiring staff to wear personal oxygen monitors

Work Process H. Waste Disposal

LBNL staff and affiliates must not:

NOTE: Even relatively small quantities can damage equipment or facilities and can crack floor tiles, damage water pipes, and damage electrical insulation on wiring. Also, consider the hazard presented by the boil-off gas when any significant quantities of a cryogenic liquid are released.

Contact LBNL Waste Management for assistance in determining the best way to dispose of cryogenic liquids.

Work Process I. Reporting Incidents: ES&H Documentation and Reporting/Notification

1. Requirements

LBNL staff and affiliates must apply the requirements for pressure safety aspects of a cryogenic-liquid-handling system as stated in PUB-3000, Chapter 7, Pressure Safety and Cryogenics.

For LBNL designed and assembled systems, the system owner must compile a data package according to the requirements in PUB-3000, Chapter 7.

Any significant accidental releases must be reported to the appropriate supervisor or work lead. Notification through an emergency and non-emergency hotline may be appropriate, depending on the severity of the release. Any personnel in the vicinity who could be exposed to the hazards of the release must be notified. A predetermined point of contact, such as the person responsible for ordering the product, could also be useful because the schedule for re-ordering may be affected by large-volume releases.

NOTE: Incidents that are reported to the non-emergency hotline are useful in tracking and analyzing accident and failure scenarios, determining trends, and changing engineering configurations or procedures.

Results of qualitative and quantitative risk assessments will be stored in a database for future reference and for use in establishing Activity Hazard Documents when required. Risk Assessments conducted in the field by persons other than the SME must be emailed to ODHCalculator@lbl.gov.

2. Guidance

Commercial (off-the-shelf) vessels may be used as is, but available owner or operator manuals should be retained for reference as part of the system data package.

29.5 References

Source Requirements Documents


Implementing Documents
PUB-3000, Chapter 7, Pressure Safety and Cryogenics


Related Documents

 

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