Routine testing of Laminar Air Flow Cabinets (LAF) with a Handheld Particle Counter Bob Latimer & Bill Bars This applications note demonstrates how the MET ONE HHPC3+ can be used to quickly classify Laminar Air Flow hoods to ISO 14644-1
Beckman Coulter Life Sciences 481 California Ave. Grants Pass, OR. 97526 www.particle.com 800-866-7889 1-541-472-6500 8/20/2014
Introduction Many industrial settings make use of Laminar Air Flow Cabinets, often referred to as LAF, Clean Hoods, Clean Benches, Laminar Flow Hoods. These enclosures are designed to minimize the likelihood of airborne contamination compromising the materials or devices being processed in the bench, for example, of electronics, optics, biological samples and medical devices.
LAF Cabinet Configuration LAF cabinets are available in both horizontal and vertical configurations. In either case, these devices provide a clean, sterile environment for the handling of materials. ISO 5 (Fed Std Class 100) HEPA filtered air continually flows over the operator’s work area to protect product or materials from contamination. HEPA or High-Efficiency Particulate Air is a type of air filter that must satisfy certain standards of efficiency. To qualify as HEPA the filter must remove 99.97% of 0.3 µm particles. This size constitutes the Most Penetrating Particle Size (MPPS), which is the most difficult size of particle to filter. Smaller and larger particles are filtered at even greater efficiency. Particle capture efficiency at 0.5µm with HEPA filtration will be significantly greater than at 0.3µm. It is at 0.5µm that periodic testing to ISO 14644-1 is typically performed. Figure 1- a typical horizontal flow cabinet design
Testing LAF Cabinet particle performance It is good practice to periodically check that an LAF Cabinet is performing to specification. Test frequency and number of sample points to test are considerations influenced by a number of factors, such as application, risk assessment, workflow and workload.
Figure 2 - The LAF set up as a workstation
Routine testing of Laminar Air Flow Cabinets
Figure 3 - Identification of sampling points
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In this example, an LAF used by a medical device manufacturer is checked every six months to ensure compliance to ISO 14644-1 Class 5. Four sampling points are selected based upon a risk assessment of the material and workflow. Two locations were selected based upon their downstream positioning relative to equipment in the HEPA filtered air flow. As a student-t test is required to be performed where areas are to be classified to ISO 14644-1 with fewer than 9 sampling locations, a further two locations were selected to reduce statistical variance.
Handheld Particle Counter – MET ONE HHPC 3+ The MET ONE HHPC+ series Handheld Particle Counter is an ideal choice for LAF monitoring and classification to ISO 5. The three channel, HHPC 3+ makes for an affordable solution. While Handheld Particle Counters sample at relatively low flow rates, typically 0.1 cubic feet per minute, an LAF cabinet can be classified in only several minutes due the small footprint of the enclosure and therefore fewer sample points necessary to be measured.
Sampling The following particle counts were taken at the four locations identified. The particle counter was set up to sample two, one minute samples with data being
Figure 4 - The MET ONE HHPC 3+ Handheld
presented in counts per cubic meter, per the ISO 14644-1 standard. LAF 1
Number of locations
Counts/m3 Sample 1 (60 sec) Sample 2 (60 sec)
Location 1 1003.5 798.4
Location 2 1890.2 809.7
4 Location 3 490.1 305.2
Location 4 706.7 353.4
Table 1 - Particle count results
Calculation of results Per the requirements of the student-t test, the student-t factor is identified from a look-up table where the number of locations to be sampled is less than or equal to nine. In the case presented here with four sampling locations, the student-t factor is 2.4
Routine testing of Laminar Air Flow Cabinets
Student T factor 95% UCL Number of locations 2 3 4 5 6 7 8 9
t 6.3 2.9 2.4 2.1 2.0 1.9 1.9 1.9
Table 2 – Student t-factor
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Three calculations to be performed are as follows. 1. The average particle count for each location 2. The mean of the averages. 3. The square of errors In this example the average of each location is calculated at the average of the two samples. The mean of the average is simply the arithmetical mean of all four averages The square of errors for each location is the square of the difference between that locations average and the mean of averages. LAF 1
Number of locations
Counts/m3 Sample 1 (60 sec) Sample 2 (60 sec) Location Average Square of errors
Location 1 1003.5 789.4 901.0 11299.7
4
Location 2 1890.2 809.7 1350.0 308358.1
Location 3 490.1 305.2 397.7 157609.0
Location 4 706.7 353.4 530.1 70013.2
Mean of averages
794.7
Table 3 – Calculating the location averages and the associated square of errors.
Next, the sum of squared errors is totaled and then divided by the number of locations less one. Finally, the 95% UCL (upper confidence limit) is calculated Sum of squared errors Sum of squared errors / (# locations – 1)
547279.9 427.1
95% UCL = ISO Class 5 Limit Result
1307.2 3520 PASS
+
x (
√ # Locations )
Table 4 – Calculating the 95% UCL and determining PASS/FAIL.
Lastly, the 95% UCL is calculated and compared to the ISO Class 5 limit which is 3,520 counts per cubic meter at 0.5µm. The result is a PASS and the LAF can is certified to ISO 5.
Table 5 – ISO 14644-1 Classification limits
Routine testing of Laminar Air Flow Cabinets
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About the MET ONE HHPC 3+ The MET ONE HHPC 3+ is a high performance yet affordable three channel instrument that is designed for contamination sensitive industrial environments. For example aerospace, optical component assembly or medical devices, where routine monitoring is conducted at 0.5µm per ISO 14644. Key product features
The easy-to-read high resolution display is fully configurable, presenting only the data you want in a clear large font
At only 1.5 lbs the MET ONE HHPC+ slim design allows single handed operation.
Quickly check or validate ISO Class 5 (FED STD Class 100) or higher clean rooms and controlled environments
Use a memory stick - grab the data and go! Or plug it in to your PC like a camera, your data appears in Excel
About the authors Bob Latimer is the Air Products manager with Beckman Coulter Life Sciences with a primary focus on contamination monitoring instrumentation for controlled environments in pharmaceutical, electronic and industrial manufacturing applications. Bob, a qualified Electrical and Electronic Engineer, has 25 years’ experience working within particle counting technology, latterly attaining his MBA at Warwick Business School, UK. Bob can be contacted via email at
[email protected]
Bill F. Bars is an Application Scientist for Beckman Coulter Life Sciences in Grants Pass, Oregon, USA. He has created and developed many of the production calibration processes and procedural tools for the Met One and HIAC branded Beckman Coulter Particle Counting products. He received his Electronics Engineering degree from DeVry Institute of Technology. He has worked for Beckman Coulter Life Sciences for nearly 18 years. You can email Bill F. Bars at:
[email protected]
Beckman Coulter Life Sciences 481 California Ave Grants Pass, Or 97526 Telephone: (541) 472-6500 www.particle.com
Routine testing of Laminar Air Flow Cabinets
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