the inferior gloves of the past. Those who
work with liquid cryogens, where accidental
splashes or spills may occur, should use
waterproof cryogenic gloves and aprons.
Gloves should fit snugly for dexterity, yet loose
enough to allow for quick removal in the
event of a splash or an immersion in liquid
cryogens. It should be noted that there are
no gloves, on the market today that are safe
for immersion in liquid cryogens.
The cryogenic apron keeps the body warm
and offers protection to the torso and legs
from cryogenic splashes and spills. Safety
shoes should be worn when cryogens are
being transported. Some cryogens such as
liquid oxygen require specialized PPE.
A small splash to or near the eye from a liquid cryogen can cause damage immediately. A face shield combined with safety
goggles provides the ideal protection for the
eyes and face.
Since there are different types of PPE depending on the cryogenic application, it helps to have periodic safety and/or hazard
inspections to determine whether workers are wearing the most
suitable apparel and using the correct equipment.
Identifying and Eliminating Risks
Since risk assessment and elimination are always the biggest
challenges for safety managers, especially in cryogenics, every
evaluation should begin with a thorough understanding of
Material Safety Data Sheets (MSDS) that describe the best procedures for handling liquid or gas cryogens. All persons working in
cryogenics should read and understand all applicable MSDS
data sheets.
Cryogenic labs and work areas should maintain a safety manual
and require all workers to be completely knowledgeable of its
contents. A procedure should be in place to ensure that the
manual is updated as necessary and that everyone is made
aware of all revisions. This should be a component of an ongoing
worker-training program, which should include the proper usage
of all PPE and other appropriate apparel. For example, shoes
should be worn that can be removed quickly in case of an accident. Pants should not have cuffs; pockets should be secured to
avoid trapping liquid cryogens, and clothing should be free of
grease. Watches and other jewelry should be removed.
The Edith Cowan manual also recommends maintaining self-contained respirators as a safety precaution in the event of an oxy-gen-depleted area.
Maintaining Safe Practices
An updated safety manual and an ongoing, thorough training
program are the foundations of a safe cryogenic environment.
One of the best references for evaluating whether policies and
procedures constitute safe practices is “Cryogenics Safety
Manual — A Guide to Good Practice” from the Cryogenics
Society of America. The society’s magazine, “Cold Facts,” is
another valuable resource.
No less important is the requirement for each manager and worker to understand the optimum use of all PPE — gloves, aprons,
goggles and face shields, all of which should be periodically
inspected and replaced if they show excessive wear. Despite the
advanced technology available in today’s PPE, safety is best
assured through implementation of the most current safety procedures for working in the ultra-cold and for handling liquid cryogens.
Keeping abreast of safety data and the information it provides will
always be on-going responsibility for safety managers.
About the Author: Laura Sweeney is vice-president of Tempshield
Cryo-Protection™ in Trenton, Maine. Since 1980, the company
has specialized in the development and manufacture of high-quality cryogenic personal protective equipment such as Cryo-Gloves® Waterproof Cryo-Gloves®, Cryo-Aprons,®and is ISO
9001:2000 certified. For more information,
please call, (800) 680-2796 or visit www.cryogloves.com.
Circle 78 on Card
The cryogenic environment has always been recognized as safety intensive. Its inherent risks are essentially similar to those faced
when handling boiling water. Burns, rapid pressure build-up and
material damage are common to both, yet there are some who
mistakenly believe that short term exposure to ultra-cold or cryogens will not harm them. The severe cold (150 K or -190 F) of
cryogenic fluids, in particular, poses risks to personal safety that
should always be a primary concern to safety managers.
Every company or institution that works with cryogenics should
have its own safety program that emphasizes laboratory safety
procedures and protection for workers. In addition, managers
should be alert to the current technology in everything from storage containers to personal protective equipment (PPE) to
increase the margin
of safety.
Understanding Cryogenics
Simply stated, cryogens are liquids that boil at specific temperatures well below atmospheric pressure. These include liquefied
forms of nitrogen, ammonia, helium, oxygen and carbon dioxide.
Cryogens must be stored in specialized containers called
“Dewars” to prevent boil-off and to assure their shelf-life. Dewars
are stored in large ventilated areas because a boil-off could rapidly render the location atmosphere inert with potentially catastrophic consequences for those trapped in it.
chemically reactive properties of liquid oxygen that can lead to
displacement and possible asphyxiation.
It takes relatively little energy to raise the temperature of cryogens
to levels that could cause a rapid boil-off. Consider that the drop
of a bolt into a cryogenic fluid is the equivalent of putting a red-hot iron into a tub of water. The result is the same for both: steam,
splashing and violent reaction. However, the problems with cryogenic fluids aren’t limited to the boil-off. The liquids can warm rapidly to ambient pressure concurrent with a large expansion of volume. When cryogens jump from 150 K to room temperature, the
volume for the same pressure doubles or, if the volume is fixed,
the pressure doubles.
It follows that anyone who works under these conditions should
fully understand the impact of all material properties of cryogens
to minimize the risk to personal safety and to avoid a potential
catastrophic or fatal accident.
Cryogenic Environment Hazards
The dangers faced while working with liquid cryogens have been
well known since the inception of the industry. The SLAC National
Accelerator Laboratory at Stanford University, in its “Short Course
on Cryogenic Safety,” offers a comprehensive list of the risks. The
following definitions are excerpted from the course.
Contact burn: Exposure of the skin to low temperatures which,
comparable to heat burns, can freeze, tear or remove skin.
Frost bite: The freezing of skin and body parts resulting from low
temperatures. The Stanford course emphasizes that frost bite from
cryogenic liquids can occur in seconds rather than minutes and
is likely to result in anything from discoloration or permanent damage to loss of a limb.
Asphyxiation: Occurs when cryogenic fluids or gas vapors displace oxygen in the air. Asphyxiation is a genuine risk in areas that
are either confined or offer minimal ventilation. In addition, some
cryogens such as carbon monoxide or fluorine are highly toxic
and may cause permanent damage or death.
Pressure build-up: The rapid pressure increase that occurs when
liquid cryogens boil-off. Again, this can be devastating should it
occur in a small confined area with inadequate ventilation.
Oxygen enrichment: By itself, oxygen is not considered flammable; however, risks for fire or explosion in the cryogenic environment increase when oxygen is present in unusually high concentrations.
Hypothermia: Not necessarily a major hazard in cryogenics, but
can occur over prolonged periods.
Cryogenic usage has become more diverse with the emergence
of new technologies. Applications can vary from frozen embryo
and chord blood preservation to cryogenic processing of high-performance engine parts. Industries such as aerospace, petrochemical and food processing have a long history with cryogenics and are more likely to have well established safety requirements. Cryogens have several common properties. The most
common is their ultra-cold temperature. Australia’s Edith Cowan
University, which operates a cryogenics laboratory, lists cryogen
boiling points at any temperature below 200 K. Information in the
university’s manual, “Procedure — The Handling and Use of
Cryogenic Fluids (2003)” should be well understood by anyone
active in the use of cryogens:
Personal Protective Equipment
“They have large liquid to gas expansion ratios…a small liquid spill
produces a very large volume of gas that can displace air in a
confined space.” The manual also warns about chemical flammability of some cryogens such as hydrogen along with the
The increase of cryogenic safety awareness over the past 25
years has given rise to the development of Personal Protective
Equipment (PPE), its importance in regard to safety, and the need
for managers to develop practices for its usage. In the early days
of cryogenics, workers wore leather or terrycloth gloves, which
were found to be unsafe because liquids could easily pass
through them resulting in the possibility of serious burns. For a
time, asbestos gloves were frequently used until they were pulled
from the market because of concerns about such diseases as
mesothelioma, a form of cancer believed related to asbestos.
The need for better and safer thermal protection led to innovative
designs in cryogenic gloves and aprons, which along with developments in materials have greatly increased the margin of safety
for all who work with cryogens.
Gloves with a multi-layered construction that provide superior thermal protection and offer dexterity and comfort have replaced
