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CSA Z23328-1-04 (R2019): Evaluating Breathing System Filter Performance Using the Standard Salt Test Method
A Detailed Technical Breakdown of the Salt Aerosol Filtration Performance Test for Anaesthetic and Respiratory Filters
Ensuring the safety and efficacy of breathing system filters (BSFs) is paramount in anaesthesia and respiratory care. CSA Z23328-1-04 (R2019), an identical adoption of ISO 23328-1:2003, provides the definitive laboratory test method for assessing the particulate filtration performance of these critical medical devices. This article provides a technical breakdown of the standard’s scope, rigorous testing requirements, and the compliance landscape for manufacturers.
Scope and Applicability
The primary scope of CSA Z23328-1-04 (R2019) is to define a standardized salt test method using a sodium chloride (NaCl) aerosol. This method is specifically designed to evaluate the particle removal efficiency of filters used in breathing systems for anaesthesia and respiratory applications, including mechanical filters and combined filter/heat and moisture exchangers (HMEs).
Scope Clarification: It is crucial to distinguish this Part 1 from ISO 23328-2 (which covers bacterial/viral filtration). CSA Z23328-1 strictly addresses physical particulate filtration performance under controlled laboratory conditions, not biological efficacy or clinical sterility assurance.
The standard applies to filters that are intended to be placed in the breathing circuit. The test method itself is independent of the filter’s specific construction material or design, allowing for objective comparison across different products.
Technical Requirements of the Salt Test Method
The standard mandates a rigorous and carefully controlled laboratory setup to ensure repeatability and comparability of results across different testing laboratories.
Aerosol Generation and Challenge
The test generates a polydisperse NaCl aerosol using a nebulizer (often a Collison type). The target Mass Median Aerodynamic Diameter (MMAD) is 0.6 µm (± 0.2 µm). This specific size is chosen because it represents the Most Penetrating Particle Size (MPPS) for mechanical filter media, making it the most challenging particle size to capture. The geometric standard deviation (GSD) of the aerosol must be kept below 1.8 to ensure an appropriate particle size distribution.
Measurement and Calculation
Particle concentrations upstream and downstream of the filter are measured using condensation particle counters (CPCs) or equivalent calibrated instruments. The filtration efficiency is calculated as a percentage:
- Efficiency (%) = [1 – (Downstream Conc. / Upstream Conc.)] × 100%
The test must be conducted at a specific flow rate declared by the manufacturer (e.g., 30 L/min for adult applications, 15 L/min for paediatric). Leak testing of the entire test circuit is mandatory prior to sample insertion. A minimum of three filter samples are typically tested to validate performance consistency.
| Parameter | Requirement |
|---|---|
| Challenge Aerosol | Sodium Chloride (NaCl) |
| Particle Size (MMAD) | 0.6 µm ± 0.2 µm |
| Geometric Standard Deviation | < 1.8 |
| Test Flow Rate | As declared by manufacturer (e.g., 30 L/min) |
| Flow Rate Tolerance | ± 5% of declared flow |
| Required Instruments | Condensation Particle Counter (CPC) or equivalent |
| Reported Result | Filtration Efficiency (%) / Penetration (%) |
Equipment Validation: The standard emphasizes that the entire test system must be validated for leaks and the aerosol generator must produce a stable output. Failure to stabilize the aerosol concentration upstream can lead to significant variances in the calculated efficiency downstream.
Implementation and Compliance Considerations
For manufacturers looking to certify their breathing system filters under CSA Z23328-1-04 (R2019), several compliance pathways and technical hurdles exist.
Testing Laboratories and QMS Integration
Testing should be conducted in a laboratory recognized for medical device testing (e.g., ISO/IEC 17025 accredited). The test report must clearly state the test conditions, flow rate, measured particle size distribution (including GSD), and the resulting filtration efficiency. Integrating this test into a Quality Management System (QMS) per ISO 13485 requires rigorous documentation of the setup, calibration of CPCs, and validation of the aerosol generation system.
Best Practice: Manufacturers should correlate the salt penetration results with the intended clinical application. Testing at multiple clinically relevant flow rates provides a more comprehensive performance profile. A filter passing the salt test at 99.9% efficiency at 30 L/min provides a strong baseline for particulate protection.
Regulatory Landscape
While Health Canada does not explicitly mandate a specific single standard for licensing, demonstrating conformity to recognized standards like CSA Z23328-1 is a standard regulatory expectation for establishing safety and effectiveness of medical devices in Canada. The CSA mark provides a strong foundation for a regulatory submission. Acceptance criteria (e.g., minimum efficiency threshold) are generally defined by the manufacturer based on the intended clinical use, but a 99.9% efficiency at the MPPS is a common industry benchmark for high-level mechanical filtration.
Critical Compliance Note: Filters tested at a single specific flow rate cannot be assumed to perform identically at significantly lower or higher flow rates. Clinicians and procurement departments must carefully match the filter’s tested specifications to the ventilation parameters of the intended patient population.
Conclusion
CSA Z23328-1-04 (R2019) remains a cornerstone standard for the objective assessment of breathing system filter performance. By adhering to the precise technical requirements of the salt test method—including strict control of the aerosol MMAD, flow rates, and particle counting—manufacturers can ensure their devices meet rigorous quality and safety benchmarks. This standard continues to support better patient outcomes in anaesthesia and respiratory care by providing a reliable, quantifiable measure of filter efficacy.
Frequently Asked Questions
Q: What is the relationship between CSA Z23328-1-04 (R2019) and ISO 23328-1:2003?
A: CSA Z23328-1-04 (R2019) is an identical adoption of ISO 23328-1:2003 for the Canadian context. The technical content and test method requirements are exactly the same. CSA does not alter the text of the original ISO standard but may add a Canadian preface, administrative notes, or bilingual requirements for the standard itself.
A: CSA Z23328-1-04 (R2019) is an identical adoption of ISO 23328-1:2003 for the Canadian context. The technical content and test method requirements are exactly the same. CSA does not alter the text of the original ISO standard but may add a Canadian preface, administrative notes, or bilingual requirements for the standard itself.
Q: How does the salt aerosol test in this standard differ from the Bacterial Filtration Efficiency (BFE) test?
A: The salt test in CSA Z23328-1 measures physical particle filtration efficiency using a polydisperse NaCl aerosol (MMAD 0.6 µm) at a specified clinical flow rate. BFE tests (e.g., ASTM F2101, EN 14683) use a biological aerosol (Staphylococcus aureus) at a fixed flow rate of 28.3 L/min to assess biological barrier performance. They evaluate different, but complementary, properties of the filter media.
A: The salt test in CSA Z23328-1 measures physical particle filtration efficiency using a polydisperse NaCl aerosol (MMAD 0.6 µm) at a specified clinical flow rate. BFE tests (e.g., ASTM F2101, EN 14683) use a biological aerosol (Staphylococcus aureus) at a fixed flow rate of 28.3 L/min to assess biological barrier performance. They evaluate different, but complementary, properties of the filter media.
Q: Is compliance with CSA Z23328-1 mandatory for all breathing system filters sold in Canada?
A: While Health Canada does not explicitly mandate CSA Z23328-1 alone for device licensing, demonstrating conformity to recognized standards is a fundamental regulatory expectation for establishing safety and effectiveness. The CSA mark derived from this standard provides robust evidence for a regulatory submission.
A: While Health Canada does not explicitly mandate CSA Z23328-1 alone for device licensing, demonstrating conformity to recognized standards is a fundamental regulatory expectation for establishing safety and effectiveness. The CSA mark derived from this standard provides robust evidence for a regulatory submission.
Q: Why is the 0.6 µm particle size specifically targeted in this test method?
A: Particles around 0.6 µm are in the transition region between diffusion and impaction/interception. They are too large to be efficiently captured by Brownian diffusion (dominant for sub-0.1 µm particles) and too small to be captured by impaction or interception (dominant for super-1 µm particles). This makes them the Most Penetrating Particle Size (MPPS) for mechanical filter media, representing the worst-case scenario for filter performance testing.
A: Particles around 0.6 µm are in the transition region between diffusion and impaction/interception. They are too large to be efficiently captured by Brownian diffusion (dominant for sub-0.1 µm particles) and too small to be captured by impaction or interception (dominant for super-1 µm particles). This makes them the Most Penetrating Particle Size (MPPS) for mechanical filter media, representing the worst-case scenario for filter performance testing.
Technical Article — Published 2026. Based on CSA Z23328-1-04 (R2019).