By Eamonn Ryan
This is the first in a series of two instalments of insights from a SAIRAC Cape Town Centre technical talk.
Thabo Mngadi (AFMS mechanical engineer). Supplied by SAIRAC Cape Town Centre
The Cape Town Centre of SAIRAC recently hosted a technical session on the critical subject of controlling airborne pathogens. The technical talk was opened by Theo van der Linde (SAIRAC vice-chairman), with the joint presentation by Thabo Mngadi (AFMS mechanical engineer) and Cassandra- Anne Baxter (ALPA sales general manager). It provided rare insights into the design and operation of laboratories capable of handling high-risk viruses.
AFMS and ALPA: two sides of a system
Behind many projects stand two sister companies:
- AFMS: a contracting and engineering firm specialising in lab design, HVAC and containment systems
- ALPA: a supplier of lab equipment, from biosafety cabinets to decontamination units
Together, they deliver turnkey solutions – AFMS handling installation and engineering, ALPA supplying specialised devices. For clients, the partnership offers a single point of accountability.
The focus covered the Bag-in Box-out (BIBO) filtration system, a vital component for safely trapping, containing and disposing of viruses and other hazardous contaminants in laboratory and healthcare environments.
Baxter opened by highlighting ALPA’s experience in designing and constructing over 150 BSL-3 laboratories across Africa, with recent projects extending into South America, including a newly commissioned facility in Ecuador. These labs are not just specialised facilities; they are frontline defences against outbreaks of dangerous pathogens. Because viruses are often airborne and invisible, she noted, the challenge lies not only in containment but also in their safe disposal.
Why standard hvac is not enough
Unlike conventional office buildings, laboratories must be engineered to handle dangerous pathogens. While standard HVAC systems rely on primary and secondary filters, these are incapable of capturing viruses. Instead, high-efficiency HEPA and ULPA filters are required, capable of trapping 99.99% of viral particles.
Mngadi explained how BIBO systems are incorporated into lab HVAC designs:
- Exhaust air from a laboratory may carry hazardous particles if an incident occurs, such as a spill of coronavirus material
- Without proper containment, maintenance staff working downstream could inadvertently be exposed
- The BIBO housing, engineered for airtight performance, prevents such scenarios by trapping viral particles and containing contaminated filters
The BIBO system goes beyond standard filtration. Each stainless-steel housing is pressure-tested and certified at the factory, ensuring it is gas-tight and compliant with global safety standards. Multiple filter types can be fitted into a single unit, including primary filters, HEPA filters, carbon filters and molecular filters for odour and chemical control.
Key advantages of BIBO systems include:
- Personnel protection: Minimising exposure during ilter replacement
- Cross-contamination prevention: Fully containing viruses and preventing them from leaking into clean environments
- Safe disposal: Contaminated filters are sealed within protective bags during removal, avoiding direct contact
Every BIBO unit is uniquely tracked using serial numbers linked to compliance certificates, ensuring that each installation can be traced back to its origin. This provides both accountability and assurance that systems meet stringent safety standards.
The presenters stressed that while BIBO systems are designed to be fail-safe, PPE remains non-negotiable for operators.
Secondary exposure – where a contaminated filter could infect a worker or escape into the community – must be prevented at all costs. The design of the BIBO unit ensures this risk is minimised through glove-integrated bags and sealed containment procedures.
As Mngadi summarised, “Standard filters will never trap a virus. It’s only through specialised systems like BIBO, combined with rigorous procedures, that we can ensure both laboratory workers and the public remain protected.”
Isolating and decontaminating the systems
A key element in managing viral containment within BIBO housings lies in the ability to isolate the system completely. Mngadi explained that a typical installation includes bubble-type dampers on both the upstream and downstream sides of the BIBO unit. These dampers enable technicians to shut off airflow during maintenance or filter replacement, isolating the housing from the rest of the exhaust system.
Once isolated, the next step is decontamination. Although the BIBO bagging system itself is designed to prevent direct contact with hazardous filters, best practice often dictates a two-tier safety strategy:
- Chemical decontamination of the filter within the housing before removal, using specialised fumigation systems or decontamination boxes
- Physical protection through the sealed bag mechanism, which encloses the filter and eliminates exposure risk during handling
This layered approach ensures that even in the unlikely event of a bag failure or operator error, pathogens are neutralised before the filter is removed.
While engineering controls provide the primary layer of safety, personal protective equipment (PPE) remains critical. For high- containment work, operators are required to wear double gloves, N95 respirators, safety glasses and coveralls. Baxter noted that ordinary surgical masks, such as those commonly used during the COVID-19 pandemic, are insufficient in BSL-3 environments. “The protective clothing is there to ensure that even if the system fails, the person doesn’t become the weak point,” Baxter emphasised.
The science of filter change-out
The session also delved into the step-by-step process of changing filters in BIBO systems. The procedure, outlined in manufacturer manuals and supported by training, is precise and methodical:
- Preparation: The correct filters, bags, straps and accessories are confirmed in advance. Tools such as torque wrenches, duct tape and change-out shelves are prepared on site.
- Isolation: The upstream and downstream dampers are closed, sealing off the housing.
- Removal: Operators work through integrated glove ports, pulling the contaminated filter into a sealed bag. Straps and metal bands are applied to ensure containment before the bag is cut free and disposed of under biohazard protocols.
- Installation: The new filter, pre-sealed within its change-out bag, is carefully guided into the housing. The bag is cinched, repositioned and secured to create the next sealed stub for future maintenance.
- Verification: Once installed, the access door is resealed and the housing undergoes integrity testing before airflow is restored.
This process, though highly controlled, underscores why only trained technicians should attempt filter replacement. As Mngadi cautioned: “The BIBO system is fail-proof in design, but only if procedures are followed to the letter.”
Seal integrity: gasket vs gel
A point of discussion during a Q&A segment concerned the different sealing mechanisms used in filter housings. Some units use gasket seals, while others rely on gel seals that form an airtight barrier when compressed against a knife-edge inside the housing. Although the two designs differ in method, both aim to maintain airtight containment. Importantly, if a gel seal is damaged, the filter must be replaced entirely to preserve integrity – there is no approved repair method.
Testing for safety
No filtration system is considered operational until it has passed a rigorous battery of tests. Among the most common are:
- Pressure decay testing: Measuring whether the housing maintains pressure without leaks
- Filter integrity testing (DOP testing): Confirming that HEPA or ULPA filters capture 99.99% of particles
- Leak testing: Using smoke or aerosol particles to identify breaches
- Visual inspections: Checking seals, gaskets and housings for signs of wear
Each test, carried out by qualified technicians, ensures compliance with international containment standards. Pressure decay testing, for example, involves sealing the housing, applying calibrated pressure and monitoring for any drop over time –with strict limits set by standards such as ANSI N510 (standard provides requirements for field testing of nuclear power plant air cleaning systems).
The conversation then turned to how HEPA filter housings fit into a full laboratory HVAC layout, using case studies from BSL-3 laboratories in Angola and Burundi. These schematics, explained by Mngadi, highlighted the airflow design principles underpinning pathogen containment.
BSL-3 facilities are designed as ‘dirty spaces’ under strict negative pressure. Supply air, delivered via ducted systems, flows in a controlled path from clean areas through anterooms into laboratory hot zones, ensuring that airborne pathogens cannot escape. Exhaust air is never recirculated back into the system, although energy recovery through heat exchangers is sometimes applied.
All potentially contaminated air is extracted via exhaust ducts, directed through biosafety cabinets (BSCs) and then channelled into BIBO housings. Although biosafety cabinets themselves are fitted with HEPA filters, Mngadi stressed that relying on them alone introduces risk: “If a filter inside a cabinet develops a tear or loses seal integrity, pathogens could bypass containment. The BIBO housing provides a secondary protective barrier – a second chance to capture those particles before they escape.”
