The Class III Biological Safety Cabinet (BSC) is a gas-tight enclosure designed for work with highly infectious microbiological agents and for the conduct of hazardous operations and provides maximum protection for the environment and the worker. A Class III BSC is typically decontaminated on a periodic basis and always before filter change out and repairs. Formaldehyde and chlorine dioxide gas are the only approved decontamination methods by NSF International. However, chlorine dioxide gas provides a much quicker cycle time than formaldehyde, is not a carcinogen, and does not leave a residue.
The Tufts New England Regional Biosafety Laboratory (RBL) is dedicated to the study of existing and emerging infectious diseases, toxin mediated diseases, and medical countermeasures important to biodefense. The facility’s two main decontamination choices are vapor-phase hydrogen peroxide (VPHP) and chlorine dioxide (CD) gas. Both agents are known to be efficacious, and both are sterilants. VPHP has been used longer, and many papers have been published on the process. Some issues of concern were that VPHP condenses and, when it does, the droplets become more aggressive or concentrated. Because of the increased concentrations, it has been documented to damage painted surfaces, epoxy surfaces, and electronics. Additionally, VPHP vapors have been shown to have limited distribution and penetration abilities. CD easily penetrates and distributes into all spaces. It covers an entire room, penetrates deeply into equipment, and gets into the hard-to-reach places. Setup is simple and requires very few extras (only 1 or 2 fans and a portable humidifier). Based on the needs to decontaminate this RBL, CD gas was the best choice as it provided complete decontamination of all surfaces within the spaces and inside the Class III BSC.
The Class III BSC can be decontaminated as part of the room (by opening the gull wing door), or it can be decontaminated on its own through use of the built-in connectors. The components needed are RH probe, mix box (which contains a humidity generator), blower motor, DC/AC controller, pressure relief scrubber, and the Minidox generator. The CD gas concentration is monitored via a gas sample port. This hose is connected to the Minidox, which then, on the basis of real-time readings, activated the gas injection system as needed. The scrubber removes any CD gas during this process. A standard cycle of 5 mg/L for 30 minutes of exposure is often used for Class III BSCs. However, due to the nature of this particular facility’s work, the cycle time was extended to 45 to 60 minutes. All biological indicators (BIs) were repeatedly killed, and no issues of corrosion were evident. All components continue to remain free of any imperfections. Due to that, chlorine dioxide gas is now the method of choice for the decontamination of Class III BSCs.
To read more about Tufts New England Regional Biosafety Laboratory’s utilization of chlorine dioxide gas for both BSC and room decontamination, click here.