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The
addresses are:
www.mgmusa.com
www.source-engineering.com
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New Faces
Employees recently joining the staff of MGM or Source
Engineering include:
B.J. McAllister
Source Engineering
Technician
3/8/00
Bethany, OK
MGM
Estimator
5/1/00
Bethany, OK
MGM
Customer Service
5/1/00
Bethany, OK
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Moisture Problems with Medical Air
Dale
Frazier,
Frazier Engineering
This month we are pleased to publish a guest columnist, Dale Frazier, President of Frazier Engineering. Frazier Engineering has been in business for 13 years and has offices in St. Louis and Weatherby, Missouri. The company specializes in building and installing code compliant medical air and vacuum systems, upgrading existing systems for code compliance and reconditioning used pumps and compressors.
"Why do we keep getting these blasted dew point alarms? We’ve got an air dryer and it’s supposed to dry the air, isn’t it? There must be something wrong with the monitor, let’s just unplug it!"
"Oh, by the way, we’ve got another ventilator with water damage. That’ll be another two or three thousand dollars to fix!"
Does any of the above sound familiar? It should. A significant number of hospitals are trying to function today with medical air systems that contain major design mistakes in the drying and monitoring equipment. Medical air suppliers who simply don’t understand the limitations and proper applications of air dryers and dew point monitors are still making these mistakes.
Let’s briefly review why water is such a problem in compressed air. Atmospheric air always contains a significant volume of water in vapor form, the exact amount being determined by temperature, barometric pressure and relative humidity. The amount of vapor that a given mass of air can hold in suspension without liquid forming is determined by the pressure and temperature of that air. Higher pressure means less volume (since air is a gas) and thus, less ability to hold water vapor. This means that when air at atmospheric pressure (14.7 PSIA) is compressed to 55 PSIG (74.7 PSIA) in a medical system, some of the water that was previously in a vapor state will condense and form liquid. Also, more water will condense if the air is cooled below the temperature at which it leaves the compressor.
To make a long story short, there WILL be water in your compressed air system no matter what kind of compressor you are using. The problem is to effectively remove it to a level that keeps the air lines dry. This brings us to dew point.
Dew point is simply the temperature at which water will condense from an air stream. If your air is at a pressure dew point of 35º F, and you never cool it below 36º F no water will form. If you cool it to 34º F, you will get water. Simple as that.
Refrigerated air dryers have been the standard for medical air for many years. These dryers are limited to a theoretical dew point of 33º F, since water will freeze at 32º F. (The old frozen air dryer problem is a topic for another time.) The actual dew point achieved by a refrigerated air dryer in good condition will be closer to 35º F. Since the NFPA-99 dictated alarm point is 39º F; you are never very far from trouble. The problem is aggravated by the practice of using dryers rated for a flow many times greater than the actual load. Refrigerated dryers and their internal moisture separators just aren’t very efficient under those conditions.
Can a refrigerated air dryer work in a medical application? Maybe. One strategy that sometimes helps is to raise the air pressure at the dryer. The dryer will remove more moisture at a higher pressure, and the dew point will be lower when the air is regulated back to the normal 55 PSIG in the system. This, of course, has some consequences for the compressors themselves. It is also important to maintain the drain traps on the dryers regularly. The dryer will only condense the water, not remove it. If the drain doesn’t work, the dryer accomplishes nothing.
For most systems, the real answer is a desiccant dryer. These dryers are becoming more popular due the fact that they will absolutely dry air to a level that will not be a problem.
What about the dew point monitor? Several major suppliers have installed chilled mirror type dew point monitors in hospitals in recent years. It is my opinion that these units are simply too maintenance intensive to ever work.
Chilled mirror technology is definitively the most accurate way to measure dew point. This is only true, however, if the mirror is kept absolutely clean. That can mean cleaning every few days in some case. That is OK for a laboratory, but very few hospital maintenance departments have the luxury of sufficient manpower to do this sort of thing. Dew point monitors with Aluminum Oxide or Lithium Chloride type sensors are readily available. While they may give up a couple of percentage points in theoretical accuracy, they are usually durable enough to give reasonable long-term services.
With the right equipment, dry, trouble free air is possible. The cost of achieving this goal is almost always much less than the cost of fighting the consequences which range from contaminated air lines to damaged air outlets and patient care devices.
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Meet the
Staff
Malcolm Pollard, Eastern Regional Manager
Malcolm Pollard joined the staff of Medical Gas Management as a technician in November, 1991. He was promoted to Eastern Region Manager in 1996 assuming responsibility for projects east of the Mississippi River.
Dealing with misinformation in the medical gas industry is probably the biggest challenge Malcolm faces on the job. But that challenge leads to a very rewarding aspect of his position.
Malcolm says that many times when he arrives at a facility to perform a certification, the facility manager is quite confident the medical gas system is in full compliance with NFPA 99. After all, that is what he has been told by the installation contractor. However, the certification inspection reveals inadequate testing and a lack of proper documentation. Malcolm finds great satisfaction in disseminating accurate information on NFPA 99 and being the resource to bring a system into code compliance.
When asked about something funny that has happened to him on the job, Malcolm says checking for moisture in medical air frequently provides a free bath. Inserting an adapter into a medical air outlet to test for moisture sometimes gives you a stream of water in the face, rather than a puff of air.
In his spare time Malcolm takes care of his lawn, flower gardens, and other associated "honey do" items. His dream is to turn a 1934 or ’35 Ford coupe or truck into a street rod.
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Beyond
The Walls…
Hidden Surprises!
This gem was uncovered during
the demolition phase of an expansion project. The number of outlets on
the zone was being tripled, which required replacing the mains with
larger pipes.
While tearing out the medical air lines, workers encountered this bright red plastic tubing hidden by gray plastic conduit. The tubing ran upstairs to something long since abandoned in the surgery department. The reducing fitting shown is galvanized iron. Neither of these materials is acceptable for distribution piping of medical air.
This globe valve does not indicate whether it is open or closed. That is why ball valves with full size ports are required for isolating medical gas pipelines.
If a fire had occurred and burned through the plastic tubing, it would have been a very unwelcome surprise.