Fume hoods and biological safety cabinets combine controlled airflow, filtration, ducting, and design features to protect samples, personnel, and the laboratory environment from harsh chemicals or infectious substances. In deciding whether a biosafety cabinet or a chemical fume hood is needed, consider the type of protection that is needed. Fume hoods protect personnel only from chemical hazards, whereas biosafety cabinets protect personnel, products and the lab environment from biological hazards and some chemical hazards. Additionally, consider how the equipment will be used. Biosafety cabinets may be appropriate if small quantities of volatiles are present, but if a professional industrial hygienist or safety officer deems the amount of volatiles to be beyond the capacity of the biosafety cabinet, then a fume hood may be more suitable. For infectious agents, a biosafety cabinet is required.

Fume hoods

Safety

Under UL Standard 1805, laboratory hoods and cabinets, including fume hoods, are investigated for fire, electrical and mechanical risk of injuries. (Most biological safety cabinets are not classified under this standard because they are not typically used for large quantities of volatile chemicals. When a safety cabinet is used as a hood, ensure that it meets the UL requirements for Electrical/Mechanical Safety [UL 61010-1], the UL requirements for Material Flammability and Effectiveness of Airflow Characteristics [UL 1805], and that it has been tested in accordance with ANSI/ASHRAE 110/1995. Some manufacturers offer safety cabinets that meet both the NSF/ANSI standards and the UL standard.)

Consider the kinds of chemicals that will be used and the type and volume of work to be conducted, as this will determine the size of the hood and the preferred material. Both ducted and ductless hoods are available; ductless models, if suitable, offer some savings and other benefits. Check local building codes and environmental regulations to be sure that installations are in compliance. Stephan Hauville, president of Erlab Inc. (Rowley, Mass), points out that, “The installation of ducted hoods can be complex, and in most instances engineering studies are needed to determine the proper rooftop ventilation and ducting requirements.”

Laboratory at Framingham State University. (Image courtesy of Erlab.)

Constant monitoring of face velocity and filtration is critical to the safety of laboratory personnel. Almost any work situation involving the use of chemicals, powders or sprays can be made safer through the use of effective capture and filtration systems. Similarly, any environment in which people and contaminated air coexist can be made safer by removing dust, pollen, bacteria or smoke from the air. Each situation must be evaluated individually to determine the best approach. Fume hoods must be designed to maintain a predictable airflow rate through the face opening. The proper combination of blower capacity and hood face-opening size will accomplish this. Blower motors and filtration units can be hood-mounted, wall-mounted or located remotely. Choose filters or filter combinations that will be most effective. The ability to swap out filter sets enables use in multiple processes.

Energy savings

According to mygreenlab.org, a single chemical fume hood can use as much energy as 3.5 households every day. Broadly speaking, ventilation systems and fume hoods can be classified into two categories: Constant Air Volume (CAV) and Variable Air Volume (VAV). In a CAV fume hood, the airflow is constant, whereas in a VAV fume hood, airflow can adjust to maintain the same air velocity and containment. Because energy consumption in fume hoods is related to the volume of air flowing through them, reducing the airflow volume in a VAV fume hood results in energy savings. Airflow volume in a fume hood is manipulated by adjusting the height of a movable sash, which acts as a barrier between the inside of the hood and the rest of the lab. The sash should be raised when working in the hood, and in most cases the sash should be lowered when work is complete to ensure personnel safety. In a VAV fume hood, lowering the sash also reduces the speed of the exhaust fan and the volume of air being exhausted by the VAV ventilation system. The energy savings from lowering the sash in a VAV fume hood can be upwards of 40%.

Other hood features

Most modern fume hoods are made of molded plastic (which resists corrosion and staining) attached to a metal frame. NuAire (Plymouth, Minn.) fume hoods are made fully out of polypropylene, with no metal frame.

Manufacturer options for fume hoods include custom sizing and adding ports, outlets and other utilities and components. The latest hoods can accommodate robotic platforms for use in the biotech and drug-discovery industries. These units can have a large footprint and many require sterile, controlled environments and increased access.

Portable fume hoods

While portable (ductless) hoods are not for use with all samples and in every situation, they do offer options and benefits relative to vented systems, such as cost savings. Because they recirculate room air, local building permits may not be required; in addition, cooled or heated room air can be retained—significant for a hood that is in operation all day. Hardware and installation costs can be lower, too. It is important that a local service provider visits annually to measure face velocity and other parameters, and to assure that the hood is operating properly and determine if maintenance is needed.

Beyond the power cord, a ductless enclosure has no external connections and thus can be placed on a cart and moved from room to room. Ductless filtration recycles existing room air while cleaning the chemical mixture. No harmful fumes or vapors are released into the environment. Filters, often composed of bonded carbon, can be safely disposed of in a landfill once saturated. Advanced monitoring and safety controls have allowed ductless hoods and filtered workstations to gain acceptance in a variety of laboratory applications. Notes Hauville, “Ductless hoods are all used with a finite and variable range of chemicals, making it important to consult manufacturers’ guides of retained chemicals or chemical listing.” Erlab publishes a list stating the chemical name, the molecular weight, the grams the filter can retain and under what conditions, the filter type needed to retain the chemical and the type of saturation detection you need.

“Since a ducted fume hood consumes more energy per year than an average house, the consumption of heated or cooled air is high and can represent for a modern fume hood an average of 20,000 cubic feet (600 m3) per hour and per fume hood. … (See official studies such as the Lawrence Berkeley National Laboratory Report on High-Performance Laboratory Fume Hood Field Test at the University of California, San Francisco. Final Report for Pacific Gas and Electric Company, October 2001). … Lastly, their working principle forces them to reject toxic substances directly in the atmosphere and their tie-in to fixed ductwork renders them immobile.” ( See https://www.americanlaboratory.com/914-Application-Notes/35173-DuctlessFiltering-Fume-Enclosure-or-Ducted-Fumehood-Selecting-the-Right-Product-in-Today-sEnvironment/.)

Biological safety cabinets

Biological safety cabinets are tested to NSF/ANSI 49, which includes basic requirements for design, construction, and performance to provide personnel, product, and environmental protection, reliable operation, durability, cleanability, noise level, illumination control, vibration control, and electrical safety. The standard includes detailed test procedures and informational annexes, including recommendations for installation, field certification tests and decontamination procedures. Input from both a qualified biosafety officer and an Environmental Health and Safety (EHS) professional is required. In addition, says John Peters of NuAire, “Product performance information should also be obtained from technically competent manufacturing representatives to assist with cabinet selection. Cabinets should be certified yearly (according to NSF/ANSI 49) or at least biannually (according to standard USP for Compounding Pharmacy Products).”

Biological safety cabinets are used in a wide range of laboratory environments for life science, clinical and industrial applications. Key to deciding which type and classification of cabinet will best meet the needs of workers, while providing optimum protection, are the type of environment and the specific applications that will be performed. The first step is to perform a detailed risk assessment with a Certified Biosafety Safety Professional (CBSP) or industrial hygienist who has knowledge of the risk levels associated with specific biological materials and chemicals that may be used in a laboratory setting. This assessment should address 1) personnel protection from harmful biological agents, 2) product protection from cross-contamination and 3) environmental protection.

The next step is to assess how those risks will be fully met by the proper class and type of biological safety cabinet. Class I cabinets offer personnel and environmental protection only. Personnel protection occurs by constant movement of air into the cabinet and away from the user. Meanwhile, the environment is protected by filtering air before it is exhausted. A Class II biosafety cabinet must meet established safety requirements for protection of product, personnel and the environment as defined by NSF/ANSI, EN12469 or another internationally recognized standard. A Class II cabinet provides personnel, product and environmental protection through HEPA filtration, laminar airflow throughout the work surface and an air barrier at the front of the cabinet by use of inflow. Within the Class II classification, subcategories have been established to define specific types of Class II cabinets in terms of design, performance and installation attributes in which varying degrees of air recirculation or exhaust airflow are required. Materials that generate gases or vapors require an exhaust connection to a facility exhaust system. The Class III cabinet was designed to handle highly infectious microbiological agents and unknown agents, and/or to conduct hazardous operations while providing maximum protection for personnel and the environment. This class of cabinet is completely gas-tight, allowing access to the work zone only through an isolation area that can be routinely decontaminated between uses. To manipulate agents, personnel wear heavy-duty rubber gloves. Exhausted HEPA-filtered air must pass through two additional HEPA filters or a HEPA filter and air incinerator before being discharged into the outdoor environment.

According to Dave Phillips, product technology specialist, biological safety cabinets and clean benches, Thermo Fisher Scientific (Waltham, Mass.), “In general, the simpler the class and type, the better. A Class II, Type A2 BSC venting the filtered exhaust into the laboratory is great for biological hazards and is the simplest of the Class II BSCs. If we are working with volatile toxic chemicals and need to convey the filtered exhaust out of the laboratory, connecting that same Class II, Type A2 BSC to an external exhaust through a canopy is easiest. It is a little more complex than the standalone version—now we need to monitor the external exhaust system and that additional system needs to be maintained. The next step up is kind of a special case. The Class II, Type B2 BSC not only exhausts the filtered air out of the laboratory; it does not even recirculate any air, filtered or not, within the cabinet. But it exhausts three times as much air, has negative static pressure or ‘suction’ requirements six to eight times greater than a canopy connection, and can only allow exhaust variations of 2% or so before it is outside the recommended velocity ranges. All of this is why the standard recommendations state that Class II, Type B2 BSCs must be connected to dedicated exhausts, i.e., one BSC connected to one duct connected to one fan on the roof. That is a much more complex system and many more things can go wrong in comparison to a simple Class II, Type A2 BSC recirculating filtered exhaust into the laboratory.”

Thermo Scientific Herasafe KS Class II, Type A2 biological safety cabinet. (Image courtesy of Thermo Fisher Scientific.)

Performance can be maximized by understanding how a biological safety cabinet functions and how to work within it. Phillips says, “For some, the BSC … provides some level of personal protection and some sort of product or sample protection. Often, no one explains how it works and no one demonstrates the BSC’s effectiveness.” Phillips notes that most Class II BSCs used in North America have validated containment, that is, “if an aerosol containing at least 100 million spores of B. subtilis is generated inside the BSC and no more than 15 can escape.” This provides an environment in which the air is up to 100,000 times cleaner than in the laboratory.

He notes, “When we do not realize that the balance of air being drawn in at the front window and the clean air flowing down from the ceiling of the BSC work area provides the protection from airborne hazards, we don’t think about how to work in a way that allows the airflow to do its job. We can work with the airflows by organizing supplies and processes to minimize the number of times we need to move our hands from inside the BSC to outside while we are working with our samples. The cleanest air is the downflow—that flow of air coming from the top of the BSC work area and flowing to the bottom. People working in cleanrooms have a useful term—“first air.” In a cleanroom, we want our most vulnerable processes placed where they receive the air first. As the air flows through the cleanroom it picks up dust and such from the items it encounters. Cleanroom air is usually the most dirty as it exits. Bringing the idea to the biosafety cabinet, we want the items or times where our work is most vulnerable to be exposed to the first air from the top of the cabinet. We don’t want our hands or other things to be over the vulnerable items where particles shedding from our hands or lab coat can be carried on to our work.”

Containment improvements have been driven by many factors over the years. Product design, airflow optimization, improved HEPA filtration and testing methods have all had a major impact on safety and performance. The single largest impact, however, derives from the 1992 Revision of the NSF Standard 49. BSCs that were submitted to NSF for product testing after 1992 had several new tests performed on them that required each manufacturer to adjust and/or improve their cabinet to assure compliance to the revised standard. These new tests included direct measurement of inflow velocity, motor/blower performance and biological safety containment performance tolerance testing. The direct inflow measurement test provides an accurate and consistent method and thus assures proper airflows are being set during the certification process; the motor/blower test verifies a minimum HEPA filter loading capacity (some manufacturers provide filter loading capacity that exceeds the minimum). Says NuAire’s Peters, “The biological safety containment performance tolerance test assures maximum product and personnel protection through the entire settable airflow range, optimizing containment performance.” While the previous NSF standard only required biological testing at the nominal air flow set point, the revised standard requires biological testing at multiple air flow set points, and challenging the BSC for abnormal airflow conditions, all of which provides more robust containment.

Cabinet and hood best practices

  • Minimize movement—Rapid movement at the air curtain in front of the cabinet can let room air in or cabinet air out; rapid movements within the cabinet cause turbulence that can lead to cross-contamination.
  • Watch pedestrians—Walking too quickly and close to the front of a BSC can disturb the air curtain.
  • Positioning—Ergonomics are important. A good lab chair helps maintain ergonomic positioning. Keep a straight and upright posture. Do not overextend your arms and keep wrists straight. With enough practice, many people can pipette ambidextrously, reducing stress on their dominant hand.
  • Keep an eye on the control panel—Airflow indicators, differential pressure monitoring, and alarm response settings provide important and ongoing information about unit performance.
  • Clear grills—Do not block the front grill with equipment, supplies or elbows as it is the source of the air curtain separating room air and work-area air.

In addition to interviews, some information in this article was taken from company websites. Research included reviewing information from NSF International, ANSI, mygreenlab and other industry sources (Mystaire, Erlab, The Baker Co., NuAire, Thermo Fisher Scientific and Airfiltronix).

Time for a new cabinet?

If your biological safety cabinet is nearing 15 years of service, it is time to replace it. Legacy units have a high probability of increased service and repair needs, a reality that is complicated by the dwindling availability of appropriate parts. Add to this improvements in ergonomics, cabinet performance and energy efficiency offered by newer models and the decision-making process tilts heavily in the direction of “replace.” NSF/ANSI Standard 49 hews to the 15-year mark as well. Notes Dave Phillips, “Actually, BSCs are going through kind of a revolution.” Older units “… could draw 800 to 1000 watts while [Thermo Fisher’s] newest, most energy-efficient models of the same size draw less than 200 watts. Depending on frequency of use and the costs of electricity … the savings can be quite significant.” Of course, reduced energy use also results in a smaller environmental burden.

Cabinet and hood spill cleanup

Post an outline of the SOPs. Have a spill kit available that contains adsorbent material, disinfectant, tongs, forceps, a waste container and personnel protection equipment (PPE)—a clean lab coat, scrubs, eyewear and nitrile gloves. Cleanup should begin immediately while the cabinet is operating. Place tubes, pipettors and any items that might have contained the spilled material into the biohazard bag or waste container. Contaminated materials should be contained inside the cabinet. Use tongs or forceps to pick up glass shards or sharps. Cover the spill with absorbent material. Apply appropriate disinfectant to the towel, working from the edges to the middle. (Spilled agent must not be resistant to the disinfectant.) Reaction time can vary depending on the material spilled and available disinfectant; 20 minutes of disinfectant contact time is usually sufficient to neutralize the contaminant. Once the spill has been contained and the disinfectant has had adequate time to react, use the towels to wipe up extra liquid. Place used towels in the biohazard bag within the cabinet. Re-treat the spill area with disinfectant and allow it to react before wiping up the spill with fresh towels. Check the spill pan under the work surface and disinfect following the same procedures noted above.

Rinse the spill area well. If bleach or other corrosive disinfectants were used, sterile water can be used to clean the spill area and then again to rinse it.

Once the cabinet has been cleaned, remove protective clothing. Thoroughly wash your hands. Run the BSC for at least 10 minutes before resuming work.

Following the above procedure promotes safety and keeps the equipment in good working order. It is time-consuming in the short term, but time conserving and cost-effective in the long run.