Table 1. Gas Supply Options
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Laboratories need to consider the impact of supply mode on their operations. Witnessing a scientist wrestling with a cylinder
is a sure sign that the laboratory has not implemented the most effective supply chain solution. Rather than a decentralized
system of cylinders, laboratories can centralize supply with a micro-bulk or bulk delivery program. These larger-volume supply
modes use liquid tanks located within the building or outside. Liquid nitrogen can then be efficiently piped to each point
of use at a lower cost per standard cubic foot (SCF) (Table 1). The supplier then refills the tank onsite, eliminating the
need to move cylinders or return residual product in "empty" cylinders. Although there can be an initial investment to provide
a decentralized gas system, they usually pay for themselves.
In general, facilities using more than 5,000 SCF per month of cylinder gas or 61 gallons of cryogen are good candidates for
a micro-bulk system. Those using in excess of 45,000 SCF per month or 500 gallons of cryogen can consider bulk supply. However,
the feasibility of a mode change is influenced by the layout and location of the laboratory. Typically, facilities located
on a ground floor, close to outside walls, and with adequate access for delivery vehicles are ideally suited for bulk or micro-bulk
supply. The cost for vacuum-jacketed piping is usually not a major concern when piping runs are short, but costs increase
as the distance increases to the point of use.
When installing micro-bulk and bulk tanks, consider telemetry systems that alert the supplier of when it is time to recharge
the tank, eliminating ordering and supply hassles.
Facilities that use one central supply for multiple uses will need to consider the requirements for all the uses. For example,
a central nitrogen supply used for both product-contacting applications and general uses would need to meet NF standards.
Most facilities can benefit from utilizing multiple supply modes. Users who have installed bulk nitrogen tanks often waste
gas on applications requiring a "small squirt" of nitrogen. This causes a large flash loss of gas when the liquid is drawn.
Nitrogen consumption can be reduced by as much as 30 percent through separating small-volume applications from the high-pressure
bulk system. This can easily be achieved by installing a separate low-pressure liquid cylinder or capabilities to fill small
containers onsite.
CRYOGEN SAFETY
Labs also need to take adequate precautions to provide protection for workers who handle cryogens. Due to their extremely
cold temperatures, cryogens will rapidly freeze human tissue on contact. Insulated gloves approved for use in cryogenic service
must be worn when operating valves, or when the potential exists for human contact with product or exposed cold piping. Gowns,
safety glasses, and face shields also should be worn to prevent injury. Transfer lines should be approved for use with cryogens
and should have a phase separator to prevent splashing.
Additionally, cryogens produce large volumes of gas when they vaporize. If a sufficient amount of liquid is vaporized, it
can create health hazards, particularly if released in a confined space. A small spill of liquid nitrogen expands to 697 times
its liquid volume when it vaporizes. This could displace oxygen, potentially creating an oxygen-poor environment. Use and
store liquid cryogens in well-ventilated areas. Cryogenic containers should not be stored in closets. Transport of cryogenic
containers on elevators should be avoided. If it is absolutely necessary to have an attendant in the elevator, the worker
should be equipped with an escape pack with supplemental breathing apparatus, and no other personnel should be in the car.
End-users should monitor oxygen levels in areas of cryogen use and never enter an area where oxygen levels are below 19.5
percent. Laboratories should work with suppliers that understand cryogen safety and can help them to source appropriate safety
gear and train workers in safe handling practices.
WHAT IT COMES DOWN TO...
People in the life sciences who use gases and cryogens are looking for solutions to the headaches and hassles they face in
buying and using these products. Making the right decisions becomes even more critical when they consider the very real dollars
associated with the problems.
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