Greening Medical Gases (And We Don't Mean Oxygen...)
Everybody is talking about being green. Engineers evaluate construction and facilities management decisions in the light of the highly coveted LEED certification, environmental impact, and relative "greenness." If reducing the environmental footprint of our facilities is the hot topic in construction generally, it's even more so in medical construction. Public money is being committed for medical projects with environmental strings attached, so whichever side of the environmental debate you sit on, it's clear that thinking green isn't going to be optional.
There has not been much talk about medical gases in this "green" context, so does that mean there's nothing to talk about?
Medical gas systems are only a small piece of even the most elaborate hospital building, so naturally the possible environmental contribution might be thought to be very small. Whether small or big, there are, in fact, interesting contributions that the medical gas industry, designers and users can make. This article will look at a few, and hopefully inspire some creative thinking for you, as well.
As with any environmental issue, "reduce, reuse, recycle" is a basic place to start. Medical gases are pharmaceuticals, and their use is determined by the medical needs of the patients. That means that the opportunity to reduce is not going to be found in telling doctors to use less. Rather, the opportunity will be found in wasting less - in the fact that many medical gas systems are not very well maintained.
A basic tenet of environmental planning is to look at the entire impact of something, not just the immediate elements. It's true that medical gases in liquid form are relatively energy intensive to produce. The most energy intensive is clearly the oxygen (which requires compression, liquification and separation of air), and for every liter of oxygen product, theoretically five times that amount of air must be processed (in fact, the amount is even greater). In addition, since it is produced at a remote site, there is an additional environmental impact in transporting the liquid or cylinders.
Ways to Lessen WasteAdding a simple leak detector to the maintenance toolkit and applying it in the annual testing regime can reduce leaks without a big maintenance burden. In many hospitals we visit, even bigger gains can be made by waste control - attention by the medical staff to flowmeters or suction regulators left on when the patient is gone. Like many programs that are "green" inspired, these can easily pay for themselves in lower gas costs. These simplest of programs probably represent the easiest gains of all and perhaps the most immediate payback.
Nitrogen is produced by the same operations as oxygen and transported in the same cylinders and liquid containers. Conversion to instrument air (IAir), an option now permitted under NFPA 99, offers for most facilities another opportunity to reduce operating costs and reduce their environmental footprint.
Not only does a cubic foot of IAir take less energy to produce, but being produced on site, it does not need to be transported or the empty cylinders carried away. As a side benefit, the cylinders don't need to be rented either, which is a big cost that is often invisible.
One of the more interesting opportunities for improvement comes from the operating characteristics of the on-site plants for medical air and medical vacuum. These systems are sized to accommodate worst-case demand, which naturally means that in ordinary times they are simply bigger than needed. We end up starting bigger motors than we would wish, more frequently than we would prefer.
We know this is bad energy management and bad for the motors, pumps and compressors, as well. It lowers the building's power factor, and thereby increases the power bill more than the motor nameplate would imply. Providing or retrofitting soft starting for machines that start so often is definitely worth considering.
Variable speed is now becoming economically feasible for the small horsepowers typical of medical applications. As an example, because of the extreme variation of vacuum demand and the elimination of the wide switch band required for start-stop operation, variable-speed vacuum pumps have been shown to save up to 50% of energy inputs. As energy costs rise, more users will find this an investment worth making. As a way to reduce environmental impact, it is one of the best opportunities of all.
A limitation is that not all medical vacuum technologies can be effectively operated with variable speed. Some simply cannot be operated at slower speeds or have limited turndown ratios, which complicate justifying the expense of the controls. Generally, oil-free or oilless pump technologies react well to variable speed. Liquid ring and lubricated technologies may not. All technologies can benefit from soft starting.
Liquid ring vacuum pumps are still widely used and specified, and have numerous advantages as a medical vacuum producer. They also are highly amenable to water recirculation, and with appropriate recirculation can have their water use reduced to as little as a gallon a minute. Compared to the 7-15 gallons typical of a "once through" machine, this is good going both with respect to the water in and the sewerage out.
The same recirculation tricks cannot be adapted to a liquid ring compressor because of contamination risks inherent with the medical air. As a result, the classic liquid ring compressor can no longer be considered a satisfactory compressor from an environmental standpoint. Some of its benefits may reemerge with some of the more modern technologies now on the horizon.
Liquid ring pumps also can use oil as a seal fluid instead of water, but this is probably a step backward from an environmental viewpoint. The oil must be supplied and disposed, and it is usually considered biohazardous when it has been used in a medical vacuum pump.
Oil is always a significant environmental problem, and elimination of oil is therefore desirable. On the air side, NFPA has solved the problem of oil use and disposal by second intent: no oil-lubricated compressor can be used for medical air production under the standard.
However, in countries where the ISO or HTM standards are followed, oil-lubricated compressors are still often applied to produce medical air. This is quite unfriendly environmentally, since now there is not only oil to supply, change and dispose on a periodic basis, but the medical air (contaminated by the compressor itself) must be cleaned up using filters, adsorbents and catalysts. Each of these is a disposal problem on its own. NFPA's simpler approach eliminates most of this.
There's not a lot of reuse or recycling to be had with medical gases. The gas, of course, cannot be reused and the naturally recyclable elements (the cylinders and containers) are already valuable enough to ensure the gas suppliers take good care of them. Filters, catalysts and absorber canisters are not particularly amenable to recycling, so they must at this time be calculated as part of the waste stream. They can be reduced by good system design, but some, like the final filter on the med air system, are irreplaceable assurances of quality and purity for the delivered medical gas product.
Another OpportunityOne last environmental opportunity is still developing. Nitrous oxide is considered a major greenhouse gas, with a greenhouse effect 296 times the same volume of carbon dioxide. While medical emissions of nitrous oxide is small compared to industrial and natural emissions, reduction of any greenhouse gas is worth achieving, especially one as potent as N2O.
Naturally, simply not installing a nitrous system is not our choice, but doubts have long existed about the desirability of nitrous oxide for many anesthesia applications. As one example, a recent meta-analysis of several anesthesia studies has suggested that anesthesia cases conducted without nitrous oxide suffer from nausea and vomiting (common anesthesia side effects) 28% less often.
This is not entirely new news - many anesthesiologists have elected to forgo nitrous on their own, and there has been an ongoing debate on the subject in the anesthesia community for many years. An emerging gas that may also come into play here is Xenon, which research shows has a potential to replace nitrous oxide but has no greenhouse impact.
With these developments it is easily conceivable that we will see nitrous oxide piping systems disappear from medical and dental projects in the near future.
In the total scope of things, the environmental impact of medical gases is small. That said, the things we can do to reduce that impact are easily achieved and virtually all of them also enjoy quick payback. Some actually can enhance medical care as well. It is well worth the small effort required to be "green" with your next medical gas project.