When an alarm goes off on your Class II biological safety cabinet, you need to know why and fast
When working in a biological safety cabinet (BSC), a flashing and blaring alarm is about the last thing a biologist wants to see or hear. If it happens, the “Working Safely with Laboratory Fume Hoods” poster from ESCO (Horsham, Penn.) says “terminate fume hood usage, close the sash completely and cease work.” This article explores alarms for Class II BSCs.
Before getting to the alarms, what is a Class II BSC? It can be used with low- to moderate-risk biological agents, which are those given a biosafety level of 1–3. These cabinets come in five types: A1, A2, B1, B2 and C1. The kind of alarm required depends on the BSC. In type A1 and A2 BSCs, an alarm goes off if the exhaust fails or the airflow goes too low. The alarm in type B1, B2 and C1 BSCs also shuts off the air supply if the system fails, as required by NSF International, which sets a standard for BSCs (NSF 49).
The NSF standard calls for an audible and visual alarm. “The basic alarms are sound and flashes of light to alert the user,” says Kara Held, science director at The Baker Company (Sanford, Maine), “but you can select upgrades to help determine the alarm type.”
Digging into the details
The NSF-required alarms also depend on how a Class II BSC is installed. “If the cabinet is exhausted, an exhaust airflow must also have an alarm present,” says Bill Peters, vice president of engineering at NuAire (Plymouth, Minn.). “Currently, there are no airflow alarm requirements for the cabinet itself.”
Still, many manufacturers add alarms to the cabinet, such as airflow alarms. “The cabinet airflow alarms offered today typically provide high- and low-airflow setpoints based off the nominal airflow setpoint,” Peters explains. “The high and low setpoints relate to biological challenge testing to assure when the alarm setpoint is reached, containment is still maintained, but the airflow is at a point where the cabinet should not be used.”
The way that an airflow alarm works depends on the design, and it can use pressure or velocity to track the airflow. “Both types of sensors must have temperature-compensation ability as they are used in laboratory environments that can vary in temperature,” Peters says. “Velocity sensors are typically the more accurate sensor type looking directly at airflow.” A pressure sensor relies on velocity pressure, which is related to the velocity of the airflow. “Both sensor types provide a digital output that communicates directly to the cabinet’s control-system microprocessor to display or reference the cabinet’s airflow and its acceptability to be within the stated set points,” he explains.
Doing away with decoding
With a basic alarm system, the rate of the sounds and flashes indicates what’s wrong. The Baker Company’s Class II BSC includes five alarms, each with a unique pattern. In a Baker BSC, a power alarm is a pattern of three one-second alarms followed by a two-second delay that repeats. “If it’s a pattern that you don’t recognize,” Held explains, “you need to look at the table in the manual.”
Baker offers an upgrade that provides a digital display to tell you what the alarm is. “You can get that on any of our Class II cabinets,” Held says. This can be very useful when going beyond the NSF-required alarms, like a power-processor fault alarm, which means that power went out in the building and a BSC needs to be reset before being used to check for any damage to the blower or other features. The meaning of an alarm coming up on the display can save the few minutes of looking up the code.
The Baker Company also offers remote monitoring, an option available from various vendors. “With this, you can hook up a BSC to the building maintenance system that monitors refrigerators and so on,” Held explains.
The alarm features that someone selects really depend on personal preference. “It’s less common to add the remote monitoring and digital display,” Held says, “but some customers love those.”
Extras for efficiency
In looking for a Class II BSC that meets the needs of the lab, it’s worth asking a few manufacturers to point out the features in their BSCs that stand out. Peters says that the alarms on NuAire’s BSCs “can be calibrated during the cabinet certification process.” They also include what he calls “a user-friendly method of displaying or referencing that the airflow is correct.”
Peters also points out that an alarm on a BSC won’t let you forget that it went off. As required by NSF standards, BSC alarms include a ring-back function that goes off if the alarm continues.
Alarms are only as good as they are accurate. NuAire BSCs include a “tolerance built in based on biological testing to avoid false alarms if the airflow is altered briefly,” says Peters. That increases the odds that an alarm indicates a safety concern.
Updating options
An older BSC that is NSF-certified must have the required alarms. The Baker Company can upgrade alarm systems and, says Held, “All of our options are backwards compatible.” In a system that functions properly and has been certified regularly and maintained well, Held adds that “it could make sense to update the alarm system.”
Don’t expect to be able to upgrade alarms on all BSCs. Peters says, “Most alarm systems are integrated or built into the cabinet’s control system from the start,” and those cannot be upgraded.
Although updating an older BSC might be fine, the cost should be considered. “Depending on the upgrades that you have in mind, it might cost almost as much as buying a new cabinet,” Held says. “So, you should assess upgrades on a case-by-case basis.”
Maybe the alarm system is not at the top of your Class II BSC features list, but it can make life safer in your lab.