In creating a life-sustaining “bubble” within a hostile laboratory environment, biological safety cabinets (BSCs) protect workers, the environment, and processes involving cells or biological tissues.
The first best-practice tip, directed mostly at chemists and analytical scientists, is that BSCs are not fume hoods. Air flow into hoods is more robust and does not protect products or processes from ambient air and its many contaminants. Fume hoods also vent to the outside, whereas BSCs may vent or recycle laboratory air through a HEPA filter, returning the scrubbed air to the laboratory. Knowing the type of protection required for product, process, and worker is the key to selecting the right BSC.
You’re not at the bench!
If asked, most users would recognize that the spaces inside BSCs are potentially hazardous. Yet, Jeff Serle, senior vice president at Germfree (Ormond Beach, FL), warns complacency easily replaces caution. “Be cognizant that you’re working in a BSC and not at your bench or at your desk. Plan your work so that when issues arise you can control what happens inside the cabinet.”
Users need to be aware that the principal safety feature on all BSCs is inward air flow. Unlike fume hoods, which only draw air through or away from the operator’s breathing zone, BSCs must also balance the HEPAfiltered downflow air. “That balance can be affected by where users stand, or their movements,” Serle says.
Devon Kramer, a sales specialist at Air Science (Fort Myers, FL), notes that even “placement of a BSC within a room is critical to assure optimal airflow.” Work planning should include each step of a workflow or experiment, including how to handle waste and avoid cross contamination. Serle suggests working from “clean to dirty” or “dirty to clean,” depending on the technician’s handedness (left to right or vice versa). “Conventionally, dirty to clean is in the left-toright direction, so materials and equipment should never move in the opposite direction, from right to left.”
Avoiding airborne contaminants
BSCs work by purifying non-sterile ambient laboratory air through HEPA filtration. Purified air is then blown downward, toward the product or process on the BSC’s work surface. Since the product or process may have contaminated this air, it passes through a second HEPA filter before being exhausted to the outside or back into the lab. So, as a general tip, labs need to maintain those filters and assure that air flow remains within specifications.
“Researchers often assume that working within a BSC guarantees a sterile work environment,” says Daniel Eisenman, PhD, director for Biosafety Services at Advarra (Research Triangle Park, NC). “However, the hood only protects from airborne particulate contaminants.”
For avoiding most sources of contamination, Eisenman offers the following tips:
- Disinfect work surfaces before and after working to minimize or eliminate surface contamination
- Ensure that materials brought into the hood are either disinfected or sterilized
- Wear personal protective equipment wherever appropriate to avoid introducing contamination from the researcher’s skin. “Humans are constantly shedding skin cells, which are covered in bacteria”
- Become familiar with aseptic technique to avoid introducing contamination
- Avoid blocking the air intake grills in front and in the back of the work surface, as this may disrupt airflow
- BSCs are not storage bins! Avoid storing materials in the hood that may disrupt airflow
- Disinfect gloves or process contact surfaces whenever they touch a non-sterile surface outside the BSC
- Don’t assume the hood’s UV light effectively disinfects the hood’s work surface. Many BSCs are equipped with UV disinfection units, but UV is no substitute for aseptic technique and thorough disinfection. UV has poor penetrating capability to disinfect liquid or solids that may be protecting microbial contaminants
- Locate BSCs away from doors and high traffic areas to avoid turbulent airflow that interferes with airflow within the hood
- Avoid open flames, which also may disrupt airflow, within the hood. “HEPA filters have been known to catch fire”
- Avoid using volatile or dangerous chemicals within the BSC. The most common BSCs (Class II, Type A2) exhaust 70 percent back into the room and provide zero protection against chemical fumes
Only as safe as the user
“Additionally, remember that BSCs must be certified upon installation, annually, and after repairs. National Sanitation Foundation (NSF) accredited certifiers ensure operation within the parameters specified by the manufacturer and the NSF49 standard for biosafety cabinets,” Eisenman adds.
As with any laboratory operation, safety is the primary concern when operating a BSC. Roger Pons, a product manager at Telstar (Bristol, PA), notes that BSC work often involves biohazards, so “regardless of the agent the user is working with, the BSC is only as safe as the individual operating it. Users should keep up with maintenance and certification schedules, and clean or disinfect the cabinet through established cleaning protocols.” Additionally, Pons urges users to keep waste from spills in a biohazard bag inside the cabinet, never outside. “Cover spills with a disinfectant towel to prevent aerosolization, and give the disinfectant time to work. After cleanup, depending on the disinfectant, a sterile water rinse should be used to avoid corrosion of the stainless steel inside the cabinet.”
Enough is enough
Scott Alderman, director of operations at the Duke Human Vaccine Institute (Chapel Hill, NC), advises lab managers not to purchase more BSC than they need, and to base decisions on understanding the hazards their work entails. “Most activities conducted in a clinical or biomedical research laboratory require a Class II Type A2 BSC. Adding a canopy connection to the building’s exhaust system, or purchasing a Type B cabinet without a sound reason increases costs and possibly increases the risk of cabinet malfunction.”
Alderman is also big on field-test certifying BSCs, per NSF/ANSI Standard 49, before initial use and at least annually thereafter. “Proper BSC performance requires balancing airflows throughout the unit.” Verifying proper function post-installation is important because “shipment and delivery subjects a BSC to shock and vibrations that can damage the unit’s integrity. Field testing is the only way to know for sure that a unit is performing as designed.”