Balancing Safety with Environmental Concerns
With most manufacturers providing solid biological safety cabinets (BSCs) with more or less standard features, total cost of ownership has become a hot-button issue with purchasers. “It all began a few years ago with energy efficiency,” says David Phillips, a technical applications specialist at Thermo Fisher Scientific (Asheville, NC). Until around 2000, exhaust fans were driven by AC permanent split capacitor motors. Manufacturers gradually switched to more advanced variable frequency drive AC motors that provided greater motor speed control. These have been standard for the last three or four years.
The “green shift” resulted from a better-educated user base that appreciates equipment that saves money while sparing the environment.
Since older motors did not compensate for filters clogging over time, airflows decreased between annual certifications, compromising contamination control and user safety. In newer cabinets, motors speed up to maintain a constant air velocity into or out of the cabinet. “They sense the increased resistance,” Mr. Phillips notes. “But the coolest thing about them is they are anywhere from 50 percent to 75 percent more energy efficient than the older models, which translates into phenomenal energy savings, and they’re much safer. Buyers really are getting more value for less money.”
Although the new motors are more expensive than the older models, this has not been reflected in the overall cost of a new BSC, according to Mr. Phillips. Energy savings can be as high as $800 per year per cabinet.
AC or DC?
In addition to driving BSC sales and marketing, environmental consciousness has become a major driver behind the push for abandoning AC motors in favor of DC designs. But as Mike Martin, general manager at ESCO Technologies (Hatboro, PA) notes, the AC-DC issue is far from straightforward. “DC motors draw fewer amps when filters are new or clean. AC motors draw higher amps with clean filters, but fewer as the filters load.”
The upshot is confusion among buyers who wish to save money but end up purchasing a particular design that is incompatible with their usage. While cabinet standards exist, most manufacturers do not adequately document performance in real-world situations.
“Anyone with the right story can sell a cabinet without any real documentation or long-term life studies. Purchasers assume they will save money long term because of low watt usage, but that is not always the case.”
Regardless of the motor type, BSCs should have a means of compensating for filter loading, and provide enough reserve motor capacity to maintain at least 90 percent of maximal air flow as filters clog. Otherwise safety is compromised and downtime increases due to the need for more frequent decontamination and filter changes.
Reducing big-ticket maintenance
Mr. Phillips says that Thermo Fisher devotes significant, ongoing effort to improving overall reliability and extending motor and filter life—two of the most noteworthy maintenance issues and, next to energy consumption, the biggest contributors to operating costs.
Unlike most laboratory products, BSCs are not “user serviceable” in any meaningful way, particularly for big-ticket items such as filters and motors. Since filters often harbor biohazardous material, they are swapped out regularly by accredited, certified, third-party service professionals who also decontaminate the BSCs, adjust any settings required as a result of installing fresh filter media, and certify that the cabinet is operating properly. Certification involves written and practical testing, continuing education, and periodic retesting. Before the advent of the newer motor designs, certified technicians also adjusted motor speed to provide adequate airflow.
Filter replacement is, at the very least, disruptive. “The cabinet is usually down for two days, and the process involves big bucks,” Martin tells Lab Manager Magazine.
One thing technicians are doing a lot less of these days is replacing motors. Older designs were rated at 10,000 to 15,000 hours of service before they required rebuilding or replacement. In the last few years, motors rated at 50,000 hours and higher—Thermo claims 100,000 hours—have become standard. Today’s motors will likely outlast the cabinets.
Perhaps the most critical (and expensive) feature is external exhaust. “The decision on whether to vent a cabinet should not be taken lightly,” Mr. Phillips cautions. Cabinets that handle toxic gases require venting, but some labs may specify venting for general safety purposes.
External exhausting significantly raises the complexity of designing and building the BSC. More important, exhaust entails a “hidden” cost for facilities in terms of the removal of expensive conditioned air.
Modern BSCs come in standard sizes with much improved usability as compared to a decade ago. For example, manufacturers have implemented ergonomic improvements, such as slanted fronts, to provide greater accessibility. Potential buyers should look for NSF certification, energy consumption and service requirements.
And, as Martin suggests, since test documentation may be hard to come by, they should ask a lot of questions.
Angelo DePalma holds a Ph.D. in organic chemistry and has worked in the pharmaceutical industry. You can reach him at email@example.com.