This policy applies to all UW–Madison faculty, staff, students and part time employees who use inert cryogenic liquids (including argon, nitrogen, and helium) in university facilities, including research and teaching laboratories. The Environment, Health & Safety Department (EH&S) has established this policy to provide a safe and healthy working environment for all faculty, staff and students. This policy is intended to ensure that facilities where inert cryogenic liquids are used and stored have the proper engineering controls and postings and that university staff are provided with the knowledge and training necessary to work safely when using inert cryogenic liquids.
Cryogenic liquids are liquefied gases that are kept in their liquid state at very low temperatures. Cryogenic liquids have boiling points below -150°C (- 238°F). Inert cryogenic liquids do not undergo chemical reactions under normal conditions and are considered to be non- toxic. The gases they give off are colorless, odorless and tasteless which can make a leak or exposure difficult to detect. Their low temperatures can cause cryogenic burns on contact with skin and embrittle materials leading to structural damage. More significantly, the high expansion ratio of these liquids increases the potential to create dangerous oxygen deficient atmospheres leading to the possibility of asphyxiation of individuals working in or entering facilities. See Appendices A and B for information on the asphyxiation hazards of inert cryogenics. Without a proper hazard analysis followed by implementation of the necessary controls, university students and staff may be at risk for an adverse event.
Note: While certain materials such as cryogenic liquid carbon dioxide do not technically fit in the definition of inert cryogenic liquids, many of the required elements outlined in the policy will be enforced as determined by EH&S.
UW–Madison EH&S has defined four risk levels of hazard for facilities that use or store inert cryogenic liquids. These levels are outlined in Table 1. Each defined level imposes requirements on engineering controls, administrative controls, postings and training. All facilities where inert cryogenic liquids are used shall be evaluated and assigned a risk level by EH&S. Once a level is assigned by EH&S staff all required actions shall be taken to minimize the risk.
In order to enact this policy the following responsibilities are assigned:
EH&S: The Environment Health & Safety Department has the responsibility to:
Principal Investigators (PIs) or Facility Managers: Principal Investigators, facility managers, or other personnel in charge of laboratories or other facilities have the responsibility to:
Note: Some of these duties can be delegated to the Lab Manager/Safety Officer or other facility personnel.
Staff and Students: Individuals working in facilities that use cryogenic liquids have the responsibility to:
UW–Madison Chemical Safety Committee: The UW–Madison Chemical Safety Committee reviews and approves policies related to the safety of university staff and students.
This section provides details on additional requirements and information on policy implementation. Table 1 provides a summary of the levels referred to in this section.
In order to evaluate the hazard of a particular room containing inert cryogenic liquids several parameters will be considered, including:
Using these criteria, the likelihood of a failure leading to an Oxygen Deficiency Hazard (ODH) will be assessed and a hazard level assigned. If the laboratory/facility operations change or the quantity of cryogenic liquid in the space is in either increased or decreased the space shall be reassessed.
The space where inert cryogenic liquids are stored or used must be properly ventilated according to National and State standards while also taking into account any additional ventilation needs due to the amount of material in that space. Under no circumstances shall inert cryogenic liquids be stored in an unventilated room.
For Level 4 facilities emergency ventilation is typically required where oxygen depletion can occur rapidly. The ventilation system will immediately increase the air exchange within the facility.
Room oxygen monitors must be in place in Level 3 and 4 facilities. Normally, these monitors will be set to alarm when the concentration of oxygen drops below 19.5%. The number of monitors needed and their placement will depend on the room dimensions, size of the cylinders, the quantity of the cylinders, the types of cryogenic gas being used, whether the gas is being piped into a room, and height of the ceiling. Liquid nitrogen is heavier than air, so it is recommended that the monitors are mounted closer to the ground as opposed to higher up in the air.
The oxygen monitors must give both audible and visual alarm when oxygen levels drop below the alarm point. The alarm must be noticeable before entering the room. In some instances the hazard evaluation will indicate the need for personal monitors to be carried by each individual entering the facility. Training and postings must include the necessary response to an alarm.
Each department/purchaser is responsible for ensuring that the oxygen monitors are operating properly and are calibrated as required. The Office of Chemical Safety will keep a record of facilities containing oxygen monitors and will ensure that maintenance is being performed by the perspective labs.
You can contact EH&S for recommendations or examples of appropriate oxygen monitors.
Administrative controls and workplace-specific rules should be in place to address any hazards in the lab. Common administrative controls that may be necessary include, but aren’t limited to:
The appropriate administrative controls will be determined during the hazard assessment.
Appropriate PPE must be worn when handling or dispensing cryogenic liquids. When handling inert cryogenic liquids it is typically necessary to wear safety goggles, closed-toed shoes, long sleeved shirts and long pants at all times. Face shields and thermal gloves should be worn whenever filling a dewar or transferring large amounts of cryogenic liquid. These items must be provided by the employer and available to anyone working with cryogens.
Cryogens should be stored in containers specifically designed to house them. The containers should be insulated and double walled. Store all cryogenic liquid containers upright in well- ventilated areas. Handle them carefully, and avoid dropping, rolling or tipping them on their sides. Cryogen tanks and containers should not be stored near elevators, walkways and unprotected platform edges or in locations where heavy moving objects may strike or fall on them.
Cryogenic liquid containers should be moved on a hand truck, cart, or other appropriate transportation method. Containers need to be secured while being transported and kept upright at all times. If inert cryogenic liquids must be transported by elevator, routes and procedures should be evaluated to ensure that the cryogens can be moved safely. In the event of a power failure a passenger would be trapped in the confined space of an elevator with the container containing the cryogenic liquid. Evaporation of the liquids could lead to displacement of oxygen.
Evaluation of the routes should take into account the amount of material being transported, the vessel used, typical evaluation rates, and ventilation in all locations, including elevators. Mitigating procedures such as sending containers alone on elevators or keeping others informed as to when cryogenic liquids are being transported may be required based on a hazard assessment.
Students and staff working with or around cryogenic liquids must be trained on the procedures for its use and be made aware of the hazards involved. Training must be documented with trainee signatures and training dates. General training can be received through UW Madison’s Office of Chemical Safety. Facility specific training must also be provided by the PI/Facility Manager or designee. The training received shall provide information on the following topics:
Any facility categorized as level 2 or higher shall have signage and/or warning information posted at the room’s entrance.
All rooms assigned as risk level 2 must be posted with a sign indicating the presence of an inert cryogenic liquid. The posting will be chosen at the discretion of the Office of Chemical Safety. The signage will be either:
Warning Sign informing the public of the presence of a cryogenic liquid. This sign indicates the potential for low oxygen environments.
Danger Sign with information on who to contact in case of emergency or other concerns. This indicates the potential for an oxygen deficiency hazard of %15 or less.
Figure 1: Example sign posting for a Level 2 facility
All rooms assigned as risk level 3 and 4 must be posted with a sign indicating the following:
Level 4 facilities must also post entry requirements and may require additional signage or restrictions.
Figure 2: Example sign posting for Level 3 and 4 facilities
|Level||Risk||General Requirements||Definition/ Typical Application|
|LEVEL 1||Cold burn risk
|Inert Cryogenic Safety Training (This includes PPE usage.)||Minimal use where a worst-case scenario (such as a Dewar spill) will not bring O2level below 18%|
|LEVEL 2||Cold Burn Risk
|Inert Cryogenic Training
Cryogen Signage and Postings: Warning/Danger (if levels can drop below %15)
Site specific training
|Typical in locations where liquid nitrogen is stored or its use does not require extensive transfer. Worst-case scenario calculations may show that O2level may drop as low as 15%. Lower levels are possible if 2 independent modes of low probability are required to reach the level.|
|LEVEL 3||Medium ODH
Impaired coordination, perception and judgment
|Inert Cryogenic Training
Cryogen Signage and Postings
|Typical in locations where large amounts of inert cryogenics are transferred or where a single failure mode can lead to oxygen levels below 15%.|
|LEVEL 4||High ODH
Mental Failure, unconsciousness or death
|Inert Cryogenic Training
Cryogen Signage and Postings
Plus some or all of the following:
|Highest hazard level. O2level may drop below 12% quickly in the event of a release or failure. The Office of Chemical Safety must be notified and a hazard assessment must be performed.|
|Oxygen Levels (%)||Symptoms of Exposure|
|19.5||Minimum oxygen level without adverse effect.|
|15 to 19||Decreased ability to work strenuously. Impaired coordination. Early symptoms.|
|12 to 14||Breathing rate increases, increase in heart rate. Impaired coordination, perception and judgment.|
|10 to 12||Breathing further increases in rate and depth, lips turn blue. Poor judgment.|
|8 to 10||Mental failure. Fainting. Nausea. Unconsciousness. Vomiting.|
|6 to 8||8 minutes – fatal, 6 minutes – 50% fatal, 4 – 5 minutes – possible recovery.|
|4 to 6||Coma in 40 seconds, Convulsions, Breathing stops, Death.|
|LABORATORY SIZE||17.5% O2||15% O2||12% O2||8% O2|
*AMOUNTS OF LIQUID NITROGEN ARE APPROXIMATE AND HAVE BEEN ROUNDED TO THE NEAREST WHOLE LITER
These percentages are calculated under the following assumptions: No ventilation, standard temperature and pressure, 8 ft ceiling height and an expansion ratio of 694