As this contamination scenario continues to repeat itself in the field, we will continue to remind our readers of the remedy to this bad situation. Please consider the following;
Have you ever wondered what is lurking in the foggy layers of a cryogenic gas? Using liquid nitrogen as an example, we open the lid of a cryogenic freezer and observe a cloud of fog emerging from the -321 degree farenheight atmosphere. The cloud is actually vaporizing air surrounding the liquid gas. So, what is in the liquid besides your company's precious samples? One can never tell unless special precautions are taken to prevent particulates and contaminants from entering the liquid via an unsuspecting delivery source.
Responding to a very recent call from an upset client, I was advised that our "dirty" liquid nitrogen had contaminated a preliminary drug run costing the company significant dollars. My investigation began immediately. As in past cases, I requested a look at the contaminated substance under a microscope side by side with a non contaminated substance under a similar microscope. My request was granted and within 30 minutes I was gowned up and in the clean room conducting my initial investigation, making my observations and taking careful notes.
First my observations were of Sample One, the clean substance. It was a pure, white powder of fine grain with no visible contaminants. Then, I moved on to the second microscope where I observed a significantly contaminated slide. The white, powdered substance contained what appeared to be specs and strands of particulates and a variety of shiny, gray items. Gathering my pages of notes, I asked to see how the process of transferring the liquid nitrogen from our vessel to the transfer vessel to the final storage vessel was accomplished.
They say the devil is in the details and in this case it was proven to be true. By request, I was led to the company liquid nitrogen storage area where the Middlesex Gases & Technologies Inc. liquid nitrogen vessels are kept. On the tank was a cryogenic transfer hose with a phase separator on the delivery end. The delivery end of the hose was on the floor. In the presence of the lab manager, quality control manager and the safety director, I picked up the hose from the floor and revealed a considerable "hair ball" of contaminants that had adhered to the phase separator end of the hose. A small, cryogenic transfer container was on the floor next to the vessel. As I continued my investigation, I spoke with the person whose duty it was to fill the cryogenic vessel with liquid nitrogen. I asked him why the hose was on the floor and he responded as others before him have, "There is no where to hang the hose".
Inspecting the cryogenic transfer container, I transferred a small amount of a gray speckled powder from the vessel to a clean envelope. I had also gathered a sample of the "hair ball" material from the phase separator in another envelope. We returned to the microscopes to make our individual observation of the materials gathered from the storage areas. The samples matched the contaminants in the bad batch in question. The samples were dust, dirt, hair and specs of concrete that were picked up from the floor on the end of the phase separator and transferred to the samples with the delivery of the liquid nitrogen.
Liquid nitrogen transfer hoses should be held in place, off the floor with a Cryo-Hanger that is mounted on the upper side of a liquid nitrogen vessel. This same precaution should be used when disconnecting and reconnecting cryogenic hoses from cryogenic freezers. Do not lay the hose down or allow it to fall on the floor. The cryogenic temperature of the hose will draw contaminants to the end of the hose like a magnet, and then deliver those contaminants to the cryogenic gas stream and into your freezer with the liquid nitrogen flow.
The Cryo-Hanger is available only from Middlesex Gases & Technologies Inc. and will prove to be very inexpensive insurance. The Cryo-Hanger part number is MTLMLCH-1 and pricing is available by calling me at the number below or calling Middlesex Gases & Technologies Inc. at 1-800-649-6704.
We take pride in earning your business daily and bringing solutions to problems that are encountered such as the aforementioned.
Specialty Gas Manager
Middlesex Gases & Technologies