When added up across an entire laboratory complex, the rental cost (and potential savings from reducing inventory) can be
To help identify overstocking, calculate cylinder turn, or length of time it takes a cylinder to travel through a site. Divide
the number of total units purchased per month into the end-of-month balance. Many users are surprised to learn how many months
cylinders sit idle in their facility, adding unnecessary costs.
For instance, if a user purchases 50 cylinders per month on average, and averages a 500 cylinder end-of-month balance, it
takes ten months for a cylinder to travel through the facility. Assuming the same user pays $5 in rental per cylinder, it
amounts to $2,500 per month or $30,000 per year. A reduction in cylinder turn from ten to five months would result in $15,000
in cost savings per year. Again, if the gas supplier is delivering gases a few times a week, even five months inventory may
Implementing better cylinder replacement procedures can help realize even more incremental savings. For liquid cryogen applications,
end-users are often willing to ignore costs if they can be assured of greater security for their research projects. On the
surface, this is understandable. Their life's work is literally in those freezers, and a disruption in service or contamination
can put millions of dollars and years of research at risk. For this reason, end- users may tend to replace cryogen cylinders
sooner than necessary.
For example, a facility will often replace liquid nitrogen cylinders on a Friday afternoon to ensure an adequate supply over
the weekend, even though the container may be half full. But a properly designed automated gas supply system can help to better
manage the changeover, leading to more efficient use of the product and added security. For both liquid containers and high-pressure
gas cylinders, a manifold system can automatically facilitate the changeover when the container has the lowest possible product.
Users can then replace the "empty" cylinder while the backup is in use. In a high-pressure gas system, this typically saves
the equivalent of one free cylinder for every six purchased. In a liquid system, some users have reduced cryogen waste by
as much as 50 percent without sacrificing a secure supply. The system also ensures that the back-up cylinder is automatically
engaged when the cylinder in use runs low, ensuring a constant supply and reducing the potential for human error.
Another source of savings is the use of appropriate backup systems. Many mechanical refrigeration systems use liquid carbon
dioxide cylinders as a backup. The need to protect years of research stored in the freezer is considered far more important
than the added cost of backup cryogens. Companies often prematurely replace backup cylinders to ensure a sufficient supply
is available in the event of a mechanical failure.
One pharmaceutical company had 30 mechanical freezers in one room, each with its own high-pressure carbon dioxide back-up
cylinder with a dip-tube to draw liquid cryogen from the cylinder. Because the laboratory could not effectively gauge volume
within the cylinders, they were changed every month regardless of the amount of cryogen remaining. At roughly $30 a cylinder,
approximately $900 per month was spent in direct costs alone. Each cylinder change took approximately 20 minutes, adding additional
labor costs and work interruptions.
The problem was solved by placing a simple scale under each cylinder. Cylinder weight was then used to determine if they were
full or empty. By actively monitoring the levels of cryogen in the cylinders, the company saved approximately $10,800 per
year in excess product costs.