Particle Counter Integration Within Your Biosafety Cabinet
The use of Class II Biosafety Cabinets (BSCs) as laminar air flow devices for the production of cell and gene therapies has rapidly increased in recent years. Once used solely for research purposes, BSCs are an increasingly obvious choice for aseptic processing of novel therapies for many reasons. BSCs produce highly consistent unidirectional HEPA filtered aseptic environments (ISO Class 5 or Grade A) while providing simultaneous user protection from biohazardous materials. BSCs are also extremely cost-effective and have drastically shorter lead times than traditional primary containment devices such as aseptic isolators.
Because BSCs are not always manufactured specifically for use in Current Good Manufacturing Practices (cGMP, or GMP) environments, extra steps may need to be implemented by aseptic processing equipment owners to ensure that BSCs are compliant with applicable GMPs. One such step is the implementation of a comprehensive environmental monitoring program within the aseptic environment of the cabinet, ensuring a therapeutic product does not become adulterated by foreign particules.
Particle Monitoring
In accordance with multiple GMP guidelines, monitoring of aseptic conditions within the cabinet’s aseptic interior must occur for both viable and non-viable particles.
Viable particles are comprised of living contaminants such as bacteria or mold. Sampling for viables has historically been performed using settling plate near the aseptic process followed by incubation and analysis for CFUs. Recently real-time viable monitoring technologies have become available - an interesting development because they reduce sampling footprint within a BSC while providing faster analysis of conditions during aseptic processes.
Non-viable particles include dust or other non-living materials that may transmit viable particles within the aseptic area. Maximum counts for non-viable particles are noted in the following tables for US and EU GMP.
US GMP (ISO 14644-1)
Maximum allowable concentrations (particles/m^3) for particles equal to and greater than 0.5 µm
|
ISO Class Number |
>0.5 µm particles/m3 |
>5.0 µm particles/m3 |
|
3 |
35 |
e |
|
4 |
352 |
e |
|
5 |
3,520 |
d, e, f |
|
6 |
35,200 |
293 |
|
7 |
352,000 |
2,930 |
|
8 |
3,520,000 |
29,300 |
|
d. Sampling and statistical limitations for particles in low concentrations make classification inappropriate. |
||
|
e. Sample collection limitations for both particles in low concentrations and sizes greater than 1 µm make classification at this particle size inappropriate, due to potential particle losses in the sampling system. |
||
|
f. In order to specify this particle size in association with ISO Class 5, the macroparticle descriptor M may be adapted and used in conjunction with at least one other particle size. |
||
EU GMP, Annex 1
Maximum permitted number of particles per m3 equal to or greater than the tabulated size
|
|
At Rest |
In Operation |
||
|
Grade |
0.5 µm |
5.0 µm |
0.5 µm |
5.0 µm |
|
A |
3,520 |
20 |
3,520 |
20 |
|
B |
3,520 |
29 |
352,000 |
2,900 |
|
C |
352,000 |
2,900 |
3,520,000 |
29,000 |
|
D |
3,520,000 |
29,000 |
Not defined |
Not defined |
A non-viable particle counter.Image courtesy of TSI Incorporated
Non-viable monitoring is fairly standardized, using an isokinetic probe (typically 1 CFM sample size) placed in the unidirectional downflow air stream of the BSC. Sampled air is collected and transferred to a particle counter for analysis. To be considered aseptic, a process must meet the requirements of the applicable cGMP guidelines such as US GMP (21 CFR 210 and 211), or EU GMP Annex 1.
Although the integration of an isokinetic probe within a BSC may seem like a straightforward practice, there are several things to consider before choosing a particle counter configuration within your cabinet. Your first decision is how a probe will be integrated into a cabinet: permanent integration, or non-permanent integration.
Permanent or Non-Permanent Integration
The first step to integrating an isokinetic probe within a BSC is selecting whether the probe will be connected to the particle counter using permanent (hard-plumbed) stainless-steel tubing, or flexible integration with non-permanent tubing.
Permanent Integration
Permanent probe integration uses stainless steel tubing, typically exiting the BSC through the center of the rear wall or an area nearest an aseptic process. The tubing connects to a particle counter adjacent to or beneath the cabinet.
Benefits to permanent installation include the use of stainless steel piping and reduced length of exposed tubing (vs. flexible integration) for easy cleaning. Also, a permanent probe can’t be inadvertently moved away from an aseptic process – this prevents an instance where Grade A air is not monitored near an aseptic process.
Disadvantages to permanent integration do exist. Aseptic monitoring is risk based, and some processes may change over time. With permanent probe integration, a process may move away from a hard-plumbed probe. To avoid this issue, some users may choose to integrate multiple probes to simultaneously sample a greater area within the BSC. Including additional sampling points requires purchasing additional particle counters, exponentially driving up costs the aseptic processing system. Provisions for permanent probe(s) within a BSC can only be provided when the cabinet is manufactured and may extend the cabinet lead time.
Non-Permanent Integration
Sample tubing (typically flexible) from an isokinetic probe is transferred out of the BSC to a particle counter placed adjacent to or beneath the cabinet. Tubing should be passed out of the cabinet using an NSF/ANSI Standard 49 approved negative pressure port or other sealed connection provided by the manufacturer to ensure maintenance of the aseptic interior within the cabinet, while preventing escape of biohazardous material. Tubing from a particle counter should never exit the front of the BSC through the sash opening because of an increased contamination risk for the aseptic cabinet interior, or potential breaching biohazards out of the cabinet towards a user.
Non-permanent isokinetic probe integration is a simpler process within a BSC with its own advantages and disadvantages.
Non-permanent integration gives the freedom to move the probe close to a process for optimal sampling. Another advantage is the ability to reposition a probe within the BSC, which can eliminate the need for multiple probes. Integration non-permanent probe tubing is possible on many standard BSCs provided they have a factory-standard a negative pressure pass-through port, shortening manufacturing lead time and reducing cost.
Disadvantages to non-permanent integration include the probe’s larger footprint (due to supportive base stand), no physical control over user positioning of the probe in the BSC, and a longer piece of tubing that must be cleaned.
A non-permanent installation of an isokinetic probe within a Class II, Type C1 BSC.
An NSF/ANSI Standard 49 approved Vacu-Pass negative pressure port.
Decision Time
Both probe installation options are compliant and reliable methods for sampling during aseptic processing. When selecting a probe integration configuration, take the extra time to evaluate your aseptic processing needs, requirements for your isokinetic probe, and your BSC manufacturer’s options for probe integration.
Have additional questions? Labconco makes GMP easy, with factory acceptance reports, IQ/OQ protocols provided free of charge with all biosafety cabinets, and renowned customer service and technical support to guide you through all stages of your compliance journey. Get in touch with one of our aseptic processing experts for help with your aseptic needs.
See how our Axiom Class II, Type C1 cabinets brought GMP compliance, flexibility, and substantial cost savings to the Children’s Mercy Research Institute – a 9 story scientific innovation hub complete with comprehensive cell and gene therapy capabilities.
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