Room Particle Count Test Used to determine the concentration of airborne particles present in a clean air cabinet or a cleanroom.
Laser particle counter has the following features:
- It displays and records the number and size of particles in air.
- It has a size discrimination capability to detect the total concentration of the particle in the required particle size ranges.
- It has a sample rate of 1 or 1.7 cfm.
- Prior to testing, verify that all aspects of the cleanroom or clean zone that contribute to its operational integrity are complete and functioning in accordance with its performance specification.
- Minimum Sampling locations:
Where A = Area of cleanroom in m2
- Ensure that the sampling locations are evenly distributed throughout the area of cleanroom or clean zone and positioned at the height of the work activity.
If the customer specifies additional sampling locations, their number and positions shall also be specified.
- Maximum permitted concentration limit
Cn is the Maximum concentration of particles (in particles per cubic meter of air)
N is the ISO Classification number.
D is the considered particle size.
- The single sample volume Vs (litres) per location is determined by using equation
Where, Cn,m = Number of Particles per m3 for the largest considered particle size specified for the relevant class
20 is the defined number of particles that could be counted if the particle concentration were at the class limit.
- The volume sampled at each location shall be at least 2 litres with a minimum sampling time at each location of 1 minute.
- When Vs is very large, the time required for sampling can be substantial. By using sequential sampling procedure, both the required sample volume and the time required to obtain samples may be reduced.
- Set up the particle counter in accordance with the manufacturer’s instructions and in compliance with the instrument calibration certificate.
- The sampling probe shall be positioned pointing into the airflow.
- If the direction of the airflow being sampled is not controlled or predictable, the inlet of the sampling probe shall be directed vertically upward.
- When the number of locations sampled is more than one and less than ten, compute the overall mean of the averages, standard deviation and 95 % upper confidence limit
- Average particle concentration at a location
Xi bar is the average particle concentration at location 1 representing any location.
Xi1 to Xin is the particle Concentrations of the individual samples.
n is the number of samples taken at the location
11. The overall mean of location averages,
X double bar is the overall mean of the location averages.
Xi1 bar to Xin bar are individual location averages, determined by using equation
m is the number of individual location averages.
12. Standard deviation of location averages,
s is the standard deviation of the location averages.
13. 95% upper confidence limit (UCL) for the overall mean
14. Where the values of the 95% UCL are given in the following table.
15. ISO standard 14644 – 1 considers that a cleanroom has met the required classification if:
- The average particle concentration at each of the particle measuring locations falls below the class limits
- The calculate 95 % UCL (if applicable) is below the class limit
The cumulative count of reference size particles for each grid space will be reported. The grid centers will be considered stations. Stations will be numbered so that recorded data by the station may be correlated to numbered locations on a schematic layout of the test area.
Maximum allowable particle counts of the reference size particles are usually as defined by a statutory standard, however, this can be determined between the client and design contractor. Also, the test state, as-built, at rest, etc. should be considered when determining acceptable particle counts.
The report may include the following information:
- Type of measurement: classification or monitoring test;
- Cleanliness classification of the installation;
- Particle size range(s) and counts;
- DPC inlet sampled flow rate and flow rate through the sensing chamber volume;
- Sample location(s);
- Sampling protocol for classification or sampling plan for monitoring;
- Occupancy state
- Other data relevant for measurement.
For More Article On SOP
- SOP For Airflow Velocity and Uniformity Test
- SOP For Temperature and Humidity Test
- SOP For Room Pressure Difference Test
- SOP For Installed Filter Leakage Test
- SOP For Airflow Direction Test or Visualization Test