Guidelines For Disinfection And Sterilization Techniques For Replacing High Efficiency Air Filters in Biosafety Cabinets

The disinfection and sterilization process during the replacement of HEPA/ULPA filters in biosafety cabinets is a core biosafety step, aimed at maximizing the protection of operators and the environment when dismantling old filters that may be contaminated with pathogens. This guide provides rigorous operating procedures and technical points.
core principle
Consider the entire replacement process as a repair operation for a 'potentially infectious device'. All technical measures revolve around "packaging, purification, and protection" to ensure that pollutants are effectively killed and sealed during the operation process.

The goal of this stage is to reduce the biological load inside the filter and chamber, creating conditions for safe disassembly.

Clarify risk level: Determine the highest risk level pathogen (such as BSL-2 or BSL-3 microorganisms) that the safety cabinet has handled. The disinfection plan must match this risk level.
Choose disinfectant: Choose a broad-spectrum, efficient, and compatible disinfectant based on the type of pathogen. Common choices include:
Chlorine containing disinfectants (such as freshly prepared 1000-5000mg/L effective chlorine solution): have strong killing power against bacteria, viruses, and fungal spores, but are highly corrosive. It is important to thoroughly remove residues after contact time.
Hydrogen peroxide (such as 3-6% hydrogen peroxide solution or composite type): broad-spectrum, low residue, suitable for various surfaces.
70% -75% ethanol or isopropanol: effective against most bacteria and viruses, but limited against non enveloped viruses and spores, commonly used for preliminary and auxiliary disinfection.
Phenolic compounds: Dilute and use according to the instructions.
Determine the disinfection method: usually combining "liquid wiping/infusion" and "gas/steam fumigation" to achieve the best effect.

Purification operation: Before the planned replacement, let the safety cabinet run at full load for at least 30 minutes without interference (for high-risk situations, it is recommended to run for more than 1 hour), using internal airflow to capture any suspended particles onto the filter.
Surface wiping and disinfection:
Wear basic personal protective equipment (lab coats, gloves, goggles).
Use a suitable disinfectant (such as 70% alcohol) to thoroughly wipe all surfaces inside the cabinet, including the inner walls, workbenches, glass windows, grilles, etc., to remove surface contamination.
Key step: Deep disinfection of the workspace (fumigation method - strongly recommended)
This is the most effective pre-treatment method that can kill microorganisms that cannot be captured by airflow and are deposited in corners and surfaces.
Method: Under the premise of ensuring safety, a "VHP/H2O2" generator can be used for circulating fumigation inside the cabinet, or formaldehyde fumigation can be used (due to safety and environmental issues, it is now rarely used and requires extremely strict control).
Simplified alternative solution: If there is no professional equipment, a non-woven fabric soaked in high concentration disinfectant (such as hydrogen peroxide) can be evenly spread on the surface of the work area after shutdown, and the front window should be closed to maintain contact for at least 1 hour, creating a local high concentration steam environment.

The replacement operator must wear:
Conjoined protective clothing (preferably disposable and liquid resistant).
Double layered gloves (inner layer medical examination gloves, outer layer thick nitrile gloves).
N95 or higher level protective mask (when handling high-risk pathogens, power air supply filter respirator (PAPR) must be used).
Goggles or full face shields.
shoe cover
Prepare biohazard waste bags, disinfectant containers, and sealing tape.

The goal of this stage is to achieve "zero leakage" or "minimize leakage" when dismantling and removing old filters.

Power off locking: After completing fumigation or contact disinfection, completely disconnect the power supply of the safety cabinet and lock it with a tag.
Secondary liquid disinfection: After the operator wears a full set of PPE, open the front window and wipe the area to be touched again with disinfectant (such as filter frame, fixing device, tool handle).

This is the core technology for preventing pollutants from escaping.
Prepare double-layer packaging: Open a large, thick biohazard waste bag in the safe cabinet work area or adjacent to its opening.
Disassemble the fixing device: Carefully remove the pressure strip, fixture, etc. of the filter, and soak all small parts in a small container containing disinfectant.
Remove and immediately seal:
Two people collaborate, one carefully loosening the filter from one side and the other stabilizing it.
Slide the old filter directly and smoothly into the prepared first layer of biohazard bag.
Key action: When the filter has fully entered the bag but has not yet touched the bottom, assist personnel to immediately wrap and tighten the bag opening upwards from the outside, minimizing air disturbance inside the bag.
Spray the bag opening with disinfectant, and then the main operator tightly ties the bag opening from the inside with zip ties or tape.
Outer layer sealing: Place the sealed first layer bag into the second biohazard bag, spray disinfectant on the bag opening, and tie it tightly by external personnel.
Surface disinfection: Immediately spray disinfectant onto the outer surface of the double-layer bag.

After removing and sealing the old filter, immediately wipe and rinse all exposed internal spaces such as the filter installation groove, static pressure box, fan chamber, etc. thoroughly and extensively with disinfectant.
Soak all disassembled inner lining panels, diffuser panels, and other components in disinfectant.
Keep the disinfectant in contact with the chamber for sufficient time (usually 20-30 minutes).
Wipe with sterile water or lint free cloth dipped in clean water to remove disinfectant residues (especially corrosive disinfectants), and dry with a clean cloth or air dry naturally.

Use the double-layer sealed old filter as highly hazardous infectious waste and send it to high-pressure sterilization as soon as possible according to laboratory biosafety regulations.
The sterilization bag must be clearly labeled with 'Biosafety Cabinet Waste HEPA Filter - Contaminated'.
It is strictly prohibited to dispose of or open it as ordinary waste without sterilization.

After confirming that the installation chamber has been cleaned and dried, a new filter can be installed.
After installation, a professional must conduct a "post installation integrity scan leak test", which is the only criterion for verifying successful installation and disinfection process without contaminating the new filter. Only after passing the inspection can the safety cabinet be reactivated.
Key precautions and taboos
Prohibition of dry operation: It is strictly prohibited to directly disassemble and remove the filter without any disinfection treatment.
Prohibition of single person operation: Two people must collaborate, with one person as the main operator and one person assisting in passing tools and sealing.
Prohibition of insufficient protection: Under no circumstances should the PPE standards be lowered.
Environmental control: Conducted in a well ventilated area, preferably within the core area of a biosafety laboratory.
Emergency plan: Prepare a spill handling kit and clarify the emergency response procedures in case of accidental contamination (such as bag rupture).
Summary process
Assess risks → Select disinfectants → Fumigation/disinfection inside the cabinet → Advanced personnel protection → Power outage → Secondary disinfection → Seal and remove the old filter in a bag → Final disinfection of the chamber → High pressure sterilization of the old filter → Installation of new filter → Mandatory leak detection verification → Record and archive.
For the vast majority of laboratories, especially those dealing with BSL-2 and above pathogens, it is strongly recommended to outsource this work to biosafety cabinet service providers with rich experience and professional disinfection equipment. They can provide standardized safety operating procedures, professional fumigation equipment, and bear corresponding biosafety risks, making them a more reliable and compliant choice.