Not Your Daddy's Fume Hood
Biological safety cabinets (BSCs) are specialized work areas that provide protection to users/operators and/or samples. BSCs are categorized as Class I, Class II or Class III, depending on their construction, airflow characteristics and exhaust systems. These classifications are based on each BSC’s suitability for samples at various biosafety levels. Class I and Class II cabinets handle Biosafety Levels 1, 2 and 3 (low to moderate risk), while Class III BSCs are intended for use with Biosafety Level 4 agents (high risk).
BSCs are distinct from other safety enclosures. Laboratory fume hoods pull air over the work item and out into the environment through a vent, whereas controlled atmosphere glove boxes are completely enclosed, protecting both users and samples through an airtight barrier. A distinguishing component of BSCs is their use of high-efficiency particle air (HEPA) filters, which scrub effluent between 99.5 percent and 99.99 percent of airborne particles, or at least 99.97 percent of particles larger than 3 microns.
Class I BSCs protect personnel and the environment only. Samples are vulnerable because workspace air is swept over them before filtration and venting. Class II cabinets represent a broad category, with varying capabilities that are further subdivided into categories A1, A2, B1 and B2. The main differentiator between Class I and Class II BSCs is that Class II cabinets employ a HEPA-filtered, vertical, unidirectional airflow within the work area. Class III BSCs, which provide the highest level of protection to both workers and samples, are reserved for highly contagious or virulent biological samples.
Class II A2 cabinets are by far the most common BSCs in use today, comprising about 95 percent of installations, according to David Phillips, technical applications specialist at Thermo Scientific (Asheville, N.C.).
Class II cabinets have open fronts. Workers are protected by the steady vertical airflow. An ongoing controversy for specifying certain Class II cabinet types involves NSF Standard 49, which states that Class II A2 and B2 cabinets are designed to handle “minute” amounts of toxic chemicals and radionuclides. “But nobody has defined the term ‘minute’ quantitatively,” admits Phillips, who works on the NSF joint committee that determines BSC specifications.
To satisfy whatever that requirement might be, and to err on the side of caution, most laboratories automatically specify the use of Class II B2 cabinets, which Phillips describes as “complex, infrastructure sensitive and 10 times trickier to run” than Class II A2 cabinets. “A lot of people get stuck with B2s, but half of them should never have been installed. Users would be much better served by canopied A2 cabinets.”
Jim Hunter, senior project engineer at Labconco (Kansas City, Mo.), suggests using B-type cabinets in situations where workers are consistently working with volatile toxic agents, isotopes or anticancer drugs that you don’t want coming back into the lab. Otherwise, the acquisition and operating costs are simply not worth it. “B cabinets cost a lot of money and use a lot of energy. Unfortunately, architects assume a B cabinet is always better because it’s more expensive or because the letter ‘B’ comes after ‘A’ in the alphabet. All too often they simply override a customer’s decision on which type of cabinet to purchase,” says Hunter.
As a former certifier of BSCs, Phillips has a unique perspective on the evolution of these cabinets. In the past, he says, cabinets were commodities that barely differed as one considered the product offerings of numerous vendors. “They basically all looked like battleships,” he says. Beginning in the 1990s, cabinets began incorporating ergonomic designs that allowed operators to move forward and backward in comfort. Enclosures became brighter and air-handling systems quieter (through the adoption of DC motors and computer-controlled airflow compensation). “Cabinets evolved from being cookie- cutter-type products to having more choices and options. It’s a really fun time to be in this industry,” says Phillips.
One improvement affecting both operating costs and the environment is energy consumption. Older-model BSCs were energy hogs, but today’s units are downright miserly. Phillips recalls an event at the University of Michigan, where one of his Thermo Fisher colleagues was accused of low-balling the power consumption of a Thermo Fisher BSC. The assembled scientists were forced to eat their words after they tested the product and measured its energy usage. The result was a paper you can find at http:// bit.ly/N9bwz.
Environmental concerns have become a huge factor in BSC purchases, according to John Peters, assistant marketing director at Nuaire (Plymouth, Minn.). “Customers look for energy efficiency as well as total cost of ownership, the life of HEPA filters and the types of motors used to drive the air handlers,” he explains. Unlike many other laboratory products, purchasers of BSCs must perform their own due diligence, as no third-party organizations provide energyefficiency ratings for cabinets.
Angelo DePalma holds a Ph.D. in organic chemistry and has worked in the pharmaceutical industry. A full-time freelance writer for more than 20 years, Angelo has written nearly 2,000 trade magazine articles on pharmaceuticals, biotechnology, materials and supporting industries. You can reach him at email@example.com.