Liquid Nitrogen Dewars
These Dewars are designed for storing and dispensing small quantities of
liquid nitrogen. Easy to operate, the snap on cap and necktube core assure
positive closure and easy access without unnecessary exposures to the
cryogen. Constructed from materials of the highest performance and quality
including an aluminum exterior, these containers are not only rugged, robust, and dependable, but also have
very high thermal efficiencies. When using liquid nitrogen, be sure to use
the
highest quality cryo-gloves that
can be found anywhere. And for those wanting to keep prepared in the event
of a surprise visit by the safety committee, don't forget the often
overlooked fact that there is an MSDS for liquid nitrogen.
While liquid nitrogen is often times belittled
in terms of its real hazards, no mistake should be made about it, one can
sustain very serious injuries if not handled properly. Before using any
dewar, be it purchased from SPI Supplies or elsewhere, make sure you are
familiar with the
guidelines
and recommendations for safe handling. We also call particular
attention to the
unique liquid nitrogen withdrawal devices available as an accessory item.
We have been told by safety experts that nitrogen, as inert as it is, causes more fatalities than
any other chemical in the laboratory. When someone is encased in a purely nitrogen atmosphere, oxygen
flow is reversed from arterial blood and tissues back into the lungs and loss of consciousness follows
within seconds. We have heard of incidents at plants, for example one individual was working on top of
a reactor, leaned over, got a blast of pure nitrogen, and pitched forward into the vessel unconscious.
In the laboratory, a similar event can occur when working with liquid nitrogen since the cold vapor concentrates
at floor level, and a technician leaning down into this cloud can be overcome. Another too common mistake is to
ride on a freight elevator with the container when transporting liquid nitrogen between floors (elevators should
have warning signs posted to strictly prohibit this practice). The staff must also be trained to overcome their
natural instinct to rush to assist an unconscious coworker since over half of workers who die in confined spaces
are attempting to rescue other workers. Since nitrogen constitutes about 78% of the air that we breathe, it is
easy to become complacent and to underestimate its dangers. If you use nitrogen in your lab, safe handling of
this dangerous gas should be an annual topic for a safety meeting to remind the staff of the risks.
These dewars are of all metal construction and are glass-free. Those dewars
that contain glass are much more fragile and less robust than the dewars
described on this webpage.
The inspiration for the proceeding two paragraphs came from a list server posting from the
Analytical Laboratory Manager's Association (ALMA).
Always remember that there are two different ways to store liquid nitrogen.
First, there are dewars of the type described on this page, which are vessels
that are open to the atmosphere so that the liquid nitrogen becomes a boiling
liquid at a pressure of one atmosphere. The other, a pressurized dewar and of
a type that is not offered by SPI Supplies, is a closed vessel, where liquid
nitrogen becomes a boiling liquid at a temperature determined by the pressure
within the vessel. This type of dewar is regulated as pressure vessels, because
there is the potential for a substantial pressure to develop within them, and
generally they are protected by a pressure relief valve.
One should note however that there is no need to utilize a pressurized
vessel for the local moving of the liquid, such as from the master supply
tank (or dewar) to some laboratory application.
Also, we should point out that we do offer a
liquid nitrogen withdrawal device
that allows the boiling liquid to create a small pressure in the dewar, forcing liquid out through a tube;
the amount of pressure buildup being controlled by safety valves.
A
liquid nitrogen refrigerator
is a device more for storing refrigerated samples than a transfer dewar. A refrigerator should not be confused with
a liquid nitrogen transfer dewar!
These dewars are designed, engineered, and manufactured for the
transportation and storage of liquid nitrogen within a laboratory facility.
They are not designed for shipment of liquid nitrogen or for transportation
in a closed vehicle on the road from one location to another. USA
customers should note that they
do not have a
Department of Transportation (USDOT) number.
When there is the need to know more about beam penetration
and interaction with your samples, try out the
Electron Flight Simulator™.
It has been highly useful in terms of modeling the electron interactions that are actually occurring in real samples.
The dewars (except for the 4 liter size) come with a standard lid, also
called the "neck tube core". It is both a mechanical cover for the opening
and an insulating cover for the top of the dewar, but it is loose enough for
the nitrogen to be able to boil away without pressure buildup. The small
4 liter dewar comes with what is called a "cap". So it is not necessary to
purchase an additional one. However, often times customers prefer to order
spare neck tube cores or caps because they modify them so that different
kinds of samples can be suspended into the dewar and kept at cryo temperatures.
Be sure you review the MSDS information before using liquid nitrogen. This
is a potential very hazardous material, yet often times it is not given the
respect it deserves. We believe that risk is greatly reduced and minimized
if
cryo gloves are used when handling liquid nitrogen.
We also believe that open faced or canvas type shoes should not be worn when
working with liquid nitrogen. Often times we hear hypothetical scenarios
meant to describe situations where the wearing of canvas (or even open faced)
shoes would be safe. But we believe it is much like the argument about
automobile seat belts: One can make a sport out of creating scenarios where
one might be safer in an accident not wearing seatbelts, but if you want the
statistics to be on your side, then you would be wise to wear a seat belt.
We believe that the same would be true for the wearing of non-canvas and
non-open-faced shoes, and indeed the best choice of shoes would be OSHA approved safety shoes.
The smallest dewar for which we offer a
liquid withdrawal device
would be the one with capacity 25 liters as described below.
There are some technical issues surrounding the use of transfer devices on the
smaller dewars, and most customers prefer to hand decant. With the heavier
dewars, however, hand decanting is not an option, and the liquid transfer
device becomes essential. This is one area where one should not seek to economize
when purchasing one of the 25 liter or larger dewars.
When using the dewars as a "refrigerator" or when the need arises for other
reasons, we recommend
Apiezon® N Cryogenic High Vacuum Grease,
which is both silicone and halogen free.
Accessories