Section: 16 | Safety in the Use of Cryogens |
Help Manual

Page of 1
Type a page number and hit Enter.
  Back to Search Results
Type a page number and hit Enter.
Additional Information
Summary of table differences
No records found.
How to Cite this Reference
The recommended form of citation is:
John R. Rumble, ed., CRC Handbook of Chemistry and Physics, 103rd Edition (Internet Version 2022), CRC Press/Taylor & Francis, Boca Raton, FL.
If a specific table is cited, use the format: "Physical Constants of Organic Compounds," in CRC Handbook of Chemistry and Physics, 103rd Edition (Internet Version 2022), John R. Rumble, ed., CRC Press/Taylor & Francis, Boca Raton, FL.


Thomas J. Bruno

Cryogens (liquified gases or cryogenic liquids) are used extensively in laboratories and in analytical instruments. A cryogen is typically defined as a liquefied gas with a normal boiling temperature of no higher than -90 °C (-130 °F, different sources cite differing upper limits). Dry ice (solid carbon dioxide, which sublimes at 194.65 K, -78.5 °C) is also used to achieve low temperatures in the laboratory but is not considered to be a cryogen. The hazards associated with the use of cryogens are actually twofold. There are hazards associated with the cryogenic fluids themselves, and there are hazards associated with the containers used to store and transport the cryogenic fluids. Here, unlike other sources, we will treat these separately (Refs. 1-7).

  1. Lemmon, E.W., Properties of Cryogenic Fluids, in CRC Handbook of Chemistry and Physics, 100th Edition, 2019.
  2. Safetygram 27, Cryogenic Liquid Containers, Air Products and Chemicals, Allentown, PA. <900-13-080-US-cryogenic-liquid-containers-safetygram-27.pdf>
  3. Safetygram 8, Liquid Argon, Air Products and Chemicals, Allentown PA. <900-13-080-US-argon-safetygram-8.pdf>
  4. Safetygram 16, Safe Handling of Cryogenic Liquids, Air Products and Chemicals, Allentown PA. <900-13-080-US-safe-handling-of-cryo-liquids-safetygram-16.pdf>
  5. Safetygram 7, Liquid Nitrogen, Air Products and Chemicals, Allentown, PA. <900-13-080-US-liquid-nitrogen-safetygram-7.pdf>
  6. Laboratory Safety Chemical Hygiene Plan (CHP), OSHA Fact Sheet, U.S. Occupational Safety and Health Administration, Washington, DC. <>
  7. Laboratory Safety and Chemical Hygiene Plan, Queensborough Community College of City University of New York, Bayside, NY, 2012. <>


The major hazards associated with the use of cryogens stem from their low temperatures, their high liquid-to-gas expansion ratios, toxicity, and air displacement. Table 1 has some important properties germane to the handling of common cryogens. The gas-to-liquid expansion ratios have a variability of up to ±5 depending on the local ambient temperature. The boiling temperatures are at atmospheric pressure (101.325 kPa). Column definitions for the table are as follows.

Column heading Definition
Name Cryogen name
Mol. form. Molecular formula of cryogen
R(approx.) Approximate gas-to-liquid expansion ratio, volume liquid:volume gas::1:R
Tbp(K) Boiling temperature, in K
tbp(C) Boiling temperature, in °C

TABLE 1. Properties of Common Cryogens

NameMol. form.R(approx.)Tbp(K)/Ktbp(C)/°C
Helium (4He)He7574.2238-268.928

Low Temperature

The primary purpose of the use of a cryogen stems from the low boiling points. The potential of severe frostbite burn is very high if a cryogen comes into contact with skin. While a thin layer of vapor formation will protect the skin initially, if a cryogen is allowed to pool (such as in clothing), the frostbite danger is very high. Protective clothing is essential and should include cryogen gloves and safety glasses. A full face shield is strongly recommended. In addition, canvas shoes are discouraged because pooling can occur in the case of spillage. Pooling can also occur in cuffs on pant legs, which should be avoided. Pants should not be tucked into shoes. A lab coat or shirt cuffs should be tucked under glove gauntlets. If skin should come in contact with a cryogen, it should be rinsed with cold water; do not apply dry heat to the affected area. If clothing has frozen to an individual due to cryogen exposure, cold water should be used to free the clothing, and emergency personnel must be summoned.

Another hazard due to the low temperature results from the ability of these fluids to embrittle materials including hoses, floor mats, and other laboratory surfaces. Of special concern is the embrittlement of electrical insulation, which can lead to a fire hazard.

Because the boiling temperature of liquid nitrogen is below that of liquid oxygen, it is possible for oxygen to condense on all surfaces or vessels cooled by liquid nitrogen. Liquid oxygen is an oxidizer that can enhance the flammability characteristics of liquids and solids that it contacts. The liquid air that is seen dripping from lines transferring liquid nitrogen can be up to 50% oxygen. If a blue tint is observed in a vessel being used with liquid nitrogen, the presence of liquid oxygen must be assumed. Additional hazards of liquid oxygen are discussed below.


The high liquid-to-gas expansion ratios listed in Table 1 show that when a cryogen is vaporized, it has the potential to displace air in a laboratory. While most cryogens are not toxic per se, they can act as simple asphyxiants. Laboratories that use cryogens must be adequately ventilated. In labs with large containers of cryogen, it is important to have an oxygen monitor with an audible alarm. Personnel, including rescue workers, should not enter areas where the oxygen concentration is below 19.5% (vol/vol) unless provided with a self-contained breathing apparatus or air-line respirator. The safe range as indicated on an oxygen monitor is between 19.5% and 23% (vol/vol). Personnel in an area of low oxygen concentration may be unaware of the condition, thus monitoring is critical.

If a person seems to become dizzy or loses consciousness while working with cryogens, they should be moved to a well-ventilated area immediately. If breathing has stopped, apply CPR and emergency personnel must be summoned.


Related to the liquid-to-gas expansion ratio is the overpressure that can result if a cryogen is allowed to warm within an enclosure. Indeed, no cryogen can remain liquid within a container; some venting must be provided. If a vent becomes disabled or is not present, a warming cryogen vaporizes and produces very high pressures based on the PVT surface of the fluid.

Reactivity and Toxicity

Some cryogens pose specific hazards or handling requirements based on their chemistry.

Liquid oxygen (LOx) cannot be permitted to contact organic materials; common organic materials include solvents and vacuum pump oil. Organic materials can be readily ignited by spark or shock after exposure to LOx, including fingerprints on a surface. Clothing saturated with oxygen is readily ignitable and vigorously burns. If LOx spills on an asphalt surface, do not walk over or roll equipment over that surface for at least one hour. While not having specific toxicity issues, if LOx is exposed to high-energy electromagnetic radiation, it can produce ozone, which solidifies at LOx temperatures. Solid ozone is unstable and toxic (upon vaporization), and explodes if disturbed.

Liquid hydrogen handling requires all of the precautions used for hydrogen gas. Liquid hydrogen should not be transferred in an atmosphere of air as it readily condenses in the liquid hydrogen, resulting in a potential explosive mixture. Liquid hydrogen must be transferred by helium pressurization in properly designed vacuum-insulated transfer lines pre-purged with helium or gaseous hydrogen. Liquid hydrogen, like liquid helium, can solidify air, which can block vents and safety relief devices. Dewars and other containers made of glass should not be used for liquid hydrogen service. Breakage makes the possibility of explosion too hazardous to risk.

Cryogenic Liquid Containers

Several different types of cryogenic liquid containers are encountered in the laboratory during routine chemical analyses, and each has their own associated hazards and precautions. It is common parlance to refer to all of these containers as Dewars, but this terminology is imprecise. The small portable containers used to assemble laboratory cold baths and the small transport containers (with loose-fitting lids and carry handles) are also known as Dewars. These containers are used at ambient pressure. The larger supply containers (from which Dewars are filled) are called liquid cylinders. These containers are pressurized, with different pressure ratings available.

Liquid Cylinders

Liquid cylinders are large heavy containers with integrated casters or a dolly to facilitate movement. At least two of these casters should be equipped with a braking mechanism. Typical volumes and weights are provided below for liquid cylinders for nitrogen, oxygen, and argon.

TABLE 2. Weights of Filled Liquid Cylinders of Common Cryogens
Volume capacity (nominal) 160 L 180 L 230 L
Tare weight, kg (lb) 114 (250) 118 (260) 141 (310)
N2 filled weight, kg (lb) 233 (513 253 (556) 303 (667)
O2 filled weight, kg (lb) 301 (662) 285 (627) 375 (825)
Ar filled weight, kg (lb) 316 (695) 342 (753) 425 (936)

Liquid helium cylinders, which often incorporate a liquid nitrogen jacket, are usually heavier than those for the common cryogens listed in Table 2. Moreover, there is a larger variety of available sizes, ranging from 50 to 500 L. The weights listed in Table 2 are typical as-filled weights. Some losses occur in transport, and the losses for helium liquid cylinders can be considerable.

The weight of these cylinders can make them challenging to handle. The personal protective equipment discussed above (cryogens) must be used when handling liquid cylinders. Cylinders should be moved by pushing, not pulling, to reduce the potential of an upset. In locations of frequent transport of liquid cylinders, bottom door sills should be removed to eliminate the potential of bouncing or rough handling. If a cylinder must be transported by elevator, a freight elevator is preferred. Personnel should not ride in the elevator car with the cylinder. The cylinder should be transported in the elevator with no personnel and be met at the receiving floor. A placard reading “CRYOGEN TRANSFER - DO NOT ENTER ELEVATOR” should be posted facing the door if the elevator is to travel more than one story.

If liquid cylinders must be transported between buildings, it is critical to use ramps and to ensure that there are no large cracks in paving that must be traversed. Note also that the casters commonly found on liquid cylinders are not rated for travel along long distances of pavement. In the event loss of control of a liquid cylinder occurs during transport, such as the cylinder begins to fall, it is usually best to simply let it go and summon qualified help as defined in the organization‘s standard operating procedures.

Liquid cylinders are pressurized and can contain up to 350 psi (2411 kPa), depending on the cylinder specifications. Pressure specifications on cylinders are sometimes confusing. The commonly encountered specifications are:

• psia (pounds-force per square inch absolute) gauge pressure plus local atmospheric pressure
• psid (psi difference) difference between two pressures, specified on the cylinder label
• psig pounds (force) per square inch, gauge
• psi-vg (psi-vented gauge) difference between the measuring point and the local pressure
• psi-sg (psi-sealed gauge) difference between a chamber of air sealed at atmospheric pressure and the pressure at the measuring point

Pressure relief devices are integral to all liquid cylinders and must remain unobstructed with frost. If the outlet fitting on a pressure relief valve is facing the same direction as the liquid or gas-dispensing valve, a fitting directing vented gas away from users should be added to protect personnel. Over-pressurization of liquid cylinders is a serious hazard; cylinders can rupture if a pressure relief valve becomes impaired or inoperative.

Dewar Flasks

Dewar flasks or simply, Dewars, are small cryogen containers used at atmospheric pressure, with or without a loose-fitting cover or cap. Smaller Dewars are usually made from an evacuated silvered-glass insert set into a metal jacket. Any exposed glass should be taped to prevent flying glass in the event of a catastrophic rupture.

When filling a small Dewar from a liquid cylinder, it is best to pre-cool the interior of the Dewar with a small amount of cryogen first, before completing the fill. Boiling and splashing generally occur when filling a warm container, so all personnel should stand clear and wear appropriate personal protective equipment as discussed above. The flask should be clean and dry before filling.

A Dewar flask should not be filled to beyond 80% of its capacity. Overfilling increases the risk of splashing and spillage. A beverage thermos bottle is NOT a substitute for a Dewar flask in the laboratory under any circumstances.

When carrying a small Dewar flask, it must be the only item being carried. Dewar flasks should be held as far away from the face as possible. Be aware of other personnel in the area.

Small Dewar flasks with liquid nitrogen are often used as cold traps in the laboratory. When instrument components are placed in the filled Dewar cold bath, it is important to insert components slowly to avoid splashing and excessive boiling. Any Pyrex wool insulation placed around the flask must not dip into the cryogen or become a vapor barrier. If liquid nitrogen acquires a blue tint, it has become contaminated with liquid oxygen, and the discussion of LOx hazards above applies.

When a Dewar cold trap is used in association with a vacuum pump, the trap must be carefully emptied periodically to avoid exposure to toxic chemicals and to prevent over pressurization should the trap run dry. Note also that venting liquid nitrogen near a vacuum pump v-belt can embrittle the belt and shorten its service life. Likewise, if the venting is near electrical cables, embrittlement of the electrical insulation can result in a fire hazard.

Page 1 of 1

Entry Display
This is where the entry will be displayed

Log In - Individual User
You are not within the network of a subscribing institution.
Please sign in with an Individual User account to continue.
Note that Workspace accounts are not valid.

Confirm Log Out
Are you sure?
Log In to Your Workspace
Your personal workspace allows you to save and access your searches and bookmarks.
Remember Me
This will save a cookie on your browser

If you do not have a workspace Log In click here to create one.
Forgotten your workspace password? Click here for an e-mail reminder.
Log Out From Your Workspace
Are you sure?
Create your personal workspace
First Name (Given)
Last Name (Family)
Email address
Confirm Password

Incorrect login details
You have entered your Workspace sign in credentials instead of Individual User sign in credentials.
You must be authenticated within your organisation's network IP range in order to access your Workspace account.
Click the help icon for more information on the differences between these two accounts.
Incorrect login details
You have entered your Individual User account sign in credentials instead of Workspace credentials.
While using this network, a personal workspace account can be created to save your bookmarks and search preferences for later use.
Click the help icon for more information on the differences between Individual User accounts and Workspace accounts.
My Account

Change Your Workspace Password
Current Password

New Password
Confirm New Password

Update your Personal Workspace Details
First Name (Given)
Last Name (Family)
Email address

Workspace Log In Reminder
Please enter your username and/or your e-mail address:

Email Address

Searching for Chemicals and Properties

The CRC Handbook of Chemistry and Physics (HBCP) contains over 700 tables in over 450 documents which may be divided into several pages, all categorised into 17 major subject areas. The search on this page works by searching the content of each page individually, much like any web search. This provides a challenge if you want to search for multiple terms and those terms exist on different pages, or if you use a synonym/abbreviation that does not exist in the document.

We use metadata to avoid some of these issues by including certain keywords invisibly behind each table. Whilst this approach works well in many situations, like any web search it relies in the terms you have entered existing in the document with the same spelling, abbreviation etc.

Since chemical compounds and their properties are immutable, a single centralised database has been created from all chemical compounds throughout HBCP. This database contains every chemical compound and over 20 of the most common physical properties collated from each of the >700 tables. What's more, the properties can be searched numerically, including range searching, and you can even search by drawing a chemical structure. A complete list of every document table in which the compound occurs is listed, and are hyperlinked to the relevant document table.

The 'Search Chemicals' page can be found by clicking the flask icon in the navigation bar at the top of this page. For more detailed information on how to use the chemical search, including adding properties, saving searches, exporting search results and more, click the help icon in to top right of this page, next to the welcome login message.

Below is an example of a chemical entry, showing its structure, physical properties and document tables in which it appears.

image of an example chemical entry
We use cookies to improve your website experience. To learn about our use of cookies and how you can manage your cookie settings, please see our Cookie Policy. By continuing to use the website, you consent to our use of cookies.
Cookie Policy

Cookie Policy

We have developed this cookie policy (the “Cookie Policy”) in order to explain how we use cookies and similar technologies (together, “Cookies”) on this website (the “Website”) and to demonstrate our firm commitment to the privacy of your personal information.

The first time that you visit our Website, we notify you about our use of Cookies through a notification banner. By continuing to use the Website, you consent to our use of Cookies as described in this Cookie Policy. However, you can choose whether or not to continue accepting Cookies at any later time. Information on how to manage Cookies is set out later in this Cookie Policy.

Please note that our use of any personal information we collect about you is subject to our Privacy Policy.

What are Cookies?

Cookies are small text files containing user IDs that are automatically placed on your computer or other device by when you visit a website. The Cookies are stored by the internet browser. The browser sends the Cookies back to the website on each subsequent visit, allowing the website to recognise your computer or device. This recognition enables the website provider to observe your activity on the website, deliver a personalised, responsive service and improve the website.

Cookies can be ‘Session Cookies’ or ‘Persistent Cookies’. Session Cookies allow a website to link a series of your actions during one browser session, for example to remember the items you have added to a shopping basket. Session Cookies expire after a browser session and are therefore not stored on your computer or device afterwards. Persistent Cookies are stored on your computer or device between browser sessions and can be used when you make subsequent visits to the website, for example to remember your website preferences, such as language or font size.

Cookies We Use and Their Purpose

We use three types of Cookies - ‘Strictly Necessary’ Cookies, ‘Performance’ Cookies and ‘Functionality’ Cookies. Each type of Cookie and the purposes for which we use them are described in this section. To learn about the specific Cookies we use, please see our List of Cookies.

1. Strictly Necessary Cookies

‘Strictly Necessary’ Cookies enable you to move around the Website and use essential features. For example, if you log into the Website, we use a Cookie to keep you logged in and allow you to access restricted areas, without you having to repeatedly enter your login details. If you are registering for or purchasing a product or service, we will use Cookies to remember your information and selections, as you move through the registration or purchase process.

Strictly Necessary Cookies are necessary for our Website to provide you with a full service. If you disable them, certain essential features of the Website will not be available to you and the performance of the Website will be impeded.

2. Performance Cookies

‘Performance’ Cookies collect information about how you use our Website, for example which pages you visit and if you experience any errors. These Cookies don’t collect any information that could identify you – all the information collected is anonymous. We may use these Cookies to help us understand how you use the Website and assess how well the Website performs and how it could be improved.

3. Functionality Cookies

‘Functionality’ Cookies enable a website to provide you with specific services or a customised experience. We may use these Cookies to provide you with services such as watching a video or adding user comments. We may also use such Cookies to remember changes you make to your settings or preferences (for example, changes to text size or your choice of language or region) or offer you time-saving or personalised features.

You can control whether or not Functionality Cookies are used, but disabling them may mean we are unable to provide you with some services or features of the Website.

First and Third Party Cookies

The Cookies placed on your computer or device include ‘First Party’ Cookies, meaning Cookies that are placed there by us, or by third party service providers acting on our behalf. Where such Cookies are being managed by third parties, we only allow the third parties to use the Cookies for our purposes, as described in this Cookie Policy, and not for their own purposes.

The Cookies placed on your computer or device may also include ‘Third Party’ Cookies, meaning Cookies that are placed there by third parties. These Cookies may include third party advertisers who display adverts on our Website and/or social network providers who provide ‘like’ or ‘share’ capabilities (see the above section on Targeting or Advertising Cookies). They may also include third parties who provide video content which is embedded on our Website (such as YouTube). Please see the website terms and policies of these third parties for further information on their use of Cookies.

To learn about the specific First Party and Third Party Cookies used by our, please see our List of Cookies.

Managing Cookies

You always have a choice over whether or not to accept Cookies. When you first visit the Website and we notify you about our use of Cookies, you can choose not to consent to such use. If you continue to use the Website, you are consenting to our use of Cookies for the time being. However, you can choose not to continue accepting Cookies at any later time. In this section, we describe ways to manage Cookies, including how to disable them.

You can manage Cookies through the settings of your internet browser. You can choose to block or restrict Cookies from being placed on your computer or device. You can also review periodically review the Cookies that have been placed there and disable some or all of them.

You can learn more about how to manage Cookies on the following websites: and

Please be aware that if you choose not to accept certain Cookies, it may mean we are unable to provide you with some services or features of the Website.

Changes to Cookie Policy

In order to keep up with changing legislation and best practice, we may revise this Cookie Policy at any time without notice by posting a revised version on this Website. Please check back periodically so that you are aware of any changes.

Questions or Concerns

If you have any questions or concerns about this Cookie Policy or our use of Cookies on the Website, please contact us by email to [email protected]

You can also contact the Privacy Officer for the Informa PLC group at [email protected].

Our Cookies

Here is a list of cookies we have defined as 'Strictly Necessary':

Taylor and Francis 'First Party' Cookies


















Here is a list of the cookies we have defined as 'Performance'.

'Third Party' Cookies

Google Analytics:





The Voluntary Product Accessibility Template (VPAT) is a self-assessment document which discloses how accessible Information and Communication Technology products are in accordance with global standards.

The VPAT disclosure templates do not guarantee product accessibility but provide transparency around the product(s) and enables direction when accessing accessibility requirements.

Taylor & Francis has chosen to complete the International version of VPAT which encompasses Section 508 (US), EN 301 549 (EU) and WCAG2.1 (Web Content Accessibility Guidelines) for its products.

Click here for more information about how to use this web application using the keyboard.

This is replaced with text from the script
This is replaced with text from the script
Top Notification Bar Dialog Header
Your Session is about to Expire!
Your session will expire in seconds

Please move your cursor to continue.