Key changes to BS EN ISO 14644-3 (2019): cleanrooms and associated controlled environments. Part 3: Test Methods. Here’s what you need to know.
The test methods for the classification of cleanrooms by airborne particles have been removed. The method is addressed in BS EN ISO 14644-1:2015. BS EN ISO 14644-3:2005 had specified methods for classification of cleanrooms by airborne particles, including particle counts for ultrafine particles and macroparticles. Ultrafine particles (nanoscale particles) are now covered in BS EN ISO 14644-12:2018 with macroparticles now contained within ISO14644-1:2015
Some terms and definitions have been modified to improve the clarity and align to the terms defined in BS EN ISO 14644-1:2015. Additional notes have been added to definitions to reference other cleanliness attributes which form part of the ISO14644 family of cleanroom standards. For example, the definition of a cleanroom now recognises that cleanliness attributes, such as chemical and microbial levels, in air and on surfaces, may be applicable.
The term Discrete Particle Counter (DPC) has been removed and replaced with Light Scattering Air Particle Counter (LSAPC). These are essentially the same instrument, with the definition improved and aligned.
Annex B is the largest part of this standard and has seen the most changes, with tests removed, modified and re-written. The clause section references for the supporting tests have also changed. The table below provides a cross-reference.
With all sections getting minor updates and improvements, the Annexes identified below have had more significant changes and these are summarised here.
B.4 Recovery Test
This test sees the introduction of a 10:1 recovery time in addition to the current 100:1 recovery time. Using 10:1 is useful when testing in the lesser classified areas such as ISO 8 or ISO 9 where excessive concentrations can be difficult to achieve and measure.
Some recommendations are given on using recovery rates to ascertain the ventilation effectiveness of a cleanroom. This can be demonstrated by comparing the recovery rate at a location in the room with the overall air change rate for the cleanroom.
B.7 Installed Filter System Leakage Test
Many of the sections have been re-written. The test now has the same acceptance criteria (0.01%) for a designated leak whether you use the aerosol photometer method or the light scattering air particle counter (LSAPC) method, so the test results are now directly comparable.
Selecting the appropriate method now has fewer restrictions. The only limitation for the aerosol photometer method is when outgassing of the oil-based test aerosol could be detrimental to the product or processes in the cleanroom. In those circumstances, the LSAPC method would be selected. Artificial aerosol generation is still likely to be required, but a solid particle can be used with the LSAPC.
The other significant change applicable to both methods is that this designated leak acceptance criteria now has two limits depending on the filter class being tested. The maximum allowable penetration is 0.01%. However, for filters with integral efficiency at MPPS of 99.95% to 99.994% the maximum allowable penetration is 0.1% (10 times more). This means HEPA filters rated H13 (EN1822-1) or ISO35H (ISO29463) could be tested against the 0.1% criteria.
Filters with efficiency below 99.95% are not commonly tested, but they can be using this method, and will require different acceptance criterion.
For the procedure for installed filter system leakage scan test with an aerosol photometer, the selection of probe size has been simplified to either a 1 x 8cm rectangular or a 3.6cm diameter circular probe. Scan rate is now stated as 5cm/s.
The required upstream concentration for the aerosol photometer method has also been updated to reflect improvement in instrument technology and reflect current best practice. So, where instruments have the capability, concentrations between 1-100mg/m3 are acceptable. The former 10-100mg/m3 and the previous 20-80mg/m3 recommendation have been removed.
The procedure for installed filter system leakage scan test with a LSAPC has been re-written. The two-stage approach remains: i.e. the initial scan followed by stationary re-measurement when potential leaks are detected.
The procedure now recommends a probe size of either 1 x 8cm rectangular probe or 3.6cm diameter circular probe. This aligns with the photometer method.
Formulae are provided for when alternative size probes are selected, for example, filter face velocities are high and isokinetic sampling could be compromised.
Another significant change is the removal of the K factor from the formulae that was previously linked to the maximum allowable penetration of the filter under test. his effectively made the maximum designated leak (allowable penetration) higher.
Achieving suitable upstream concentrations, especially if oil-based aerosol generation is not possible, is very important when selecting the LSAPC method. Not achieving these concentrations will significantly reduce the probability of finding leaks.
The procedure for overall leak test of filters mounted in ducts or air handling units has been slightly modified to improve clarity. The acceptance criterion is now based on the main unified criteria discussed earlier.
B.11 Segregation Test
This is a new test and provides a method for assessing the effectiveness of segregating two areas, by means of airflow. This test is performed across an opening between two areas. For example, an open-fronted unidirectional flow workstation (critical area) and the background room (less critical area).
The method involves generation of contamination (particles) in one area (the lesser classified or less critical area) and determining the level of contamination that reaches the more critical area. A particle counter is used to measure the particles in both areas (with a diluter for the contaminated area). A formula is provided to determine a protection index.
Annex C – Test Apparatus
This Annex has been modified to align the criteria used to determine suitable test instruments (apparatus). Each apparatus now has three criteria to meet for suitability:
- Measuring limits
- Maximum permissible error
It highlights the need to ensure calibration points are within the range of use, but calibration frequency requirements have been removed.
The new standard is published and available to purchase through BSI at www.shop.bsigroup.com