Clean room grade and level - air cleanliness level

2019-02-15 15:11:05   Editor: 钜宏股份    0

Air cleanliness class: A standard for dividing a unit of air in a clean space by a maximum concentration limit greater than or equal to the particle size under consideration. Test with empty and static methods.


Yuhong shares to let you know the clean room grade and level - air cleanliness level.


Generally, there are grades in the clean room. When using multiple processes, different air cleanliness levels should be used according to different requirements of each process, and the grades should be determined according to the process requirements.


The cleanliness level and the classification of the clean area of the pharmaceutical industrial medicine production process shall be determined by reference to the process content of the preparation and raw material medicines and the environmental area division in the "Good Manufacturing Practices". The cleanliness of the clean room for drug production is divided into four grades.


Under the premise of meeting the production process requirements, firstly, clean clean or partial air purification with low cleanliness level should be adopted; secondly, partial work area air purification and first-grade city air purification can be combined or comprehensive air purification can be adopted.


Introduction


Cleanrooms and associated controlled environments control airborne particulates at appropriate levels to complete pollution-sensitive activities. Products and processes in the aerospace, microelectronics, pharmaceutical, medical device, food, and healthcare industries benefit from the control of suspended pollutants.


The ISO rating specified in this part of GB/T 25915 can be used as a technical condition for air cleanliness in clean rooms and related controlled environments. Not only is there a procedure for determining the concentration of airborne particles, but also a standard method of detection.


This section defines the particle size range for particle concentration limits. The level of cleanliness can be determined by the standard program provided in this section based on the concentration of airborne particles that are smaller or larger than the particle size of interest.


This section is one of a series of standards for clean room and pollution control. In addition to the concentration of airborne particulates, many factors must be considered in the design, technical conditions, operation and management of cleanrooms and other controlled environments. In other parts of this standard, there are details in this regard.


In some cases, the relevant regulatory agencies may impose additional policies or restrictions. In this case, it may be necessary to make appropriate adjustments to the standard detection method.


Clean room and related controlled environment


Part 1: Air cleanliness level


1 Scope


The air cleanliness level of the clean room and related controlled environment in this part of GB/T25915 is based solely on the concentration of airborne particles in it,


The concentration refers to the total number of particles having a particle diameter greater than or equal to the threshold (lower limit) particle diameter, and the specified width (lower limit) particle diameter is 0.1 μm to 5 μm. This department does not establish a cleanliness level of the total number of particles other than the specified particle size from 0.1 μm to 5 μm. However, the U descriptor and the M descriptor can be used to represent the total number of ultrafine particles (<0. 1 μm) and large particles (>5 μm), respectively. This section cannot be used to describe the physical, chemical, radiological or surviving properties of airborne particles.


Note: The actual distribution of particle concentrations greater than or equal to a particle size is generally difficult to predict and usually varies over time.


2 terms and definitions


The following terms and definitions apply to this document.


2. 1 general


2. 1.1


Clean room cleanroom


A room with controlled airborne particle concentration is constructed and used in such a way as to minimize the number of particles that enter, generate, and retain in the room. Other relevant parameters such as temperature, humidity, and pressure in the room are controlled as required.


2. 1. 2


Clean zone


The special space controlled by the concentration of airborne particles is constructed and used in such a way as to minimize the number of particles that are generated, retained, and retained in the zone. The temperature, humidity, pressure and other related parameters are controlled as required.


Note: The clean area can be open or closed, either in or out of the clean room.


2. 1. 3


Facility installation


All related structures, air handling systems, and clean rooms for services, utilities, or one or more such clean areas.


2. 1. 4


Cleanliness classification


Cleanliness grouping classification


The level of cleanliness (or the process of determining, leveling) by airborne particle concentration in a clean room or clean zone, expressed in ISO N class. The cleanliness level represents the maximum allowable concentration of particles of the particle size (expressed as the number of particles per cubic meter of air).


Note 1: For the concentration calculation, see Equation (1) of 3. 2 .


Note 2: The scope of this section is limited to ISO Level 1 - ISO Level 9.


Note 3: The level of particle size in this section is limited to the range of 0.1 μm 5 μm (lower threshold). Air cleanliness with a specified threshold particle size outside this range can be described and illustrated (but not graded) using the U descriptor and the M descriptor (see 2.3.1 and 2.3.2).


Note 4: The ISO rating can be decimal, with a minimum increment of 0.1, ISO 1. 1 - ISO 8. 9.


Note 5: Cleanliness level can be applied to all 3 occupancy states


2. 2 airborne particles


2. 2. 1


Particle


The cumulative solid or liquid material with a particle size threshold (lower limit) in the range of 0.1 μm 5 μm.


2. 2. 2

Particle size


The diameter of the sphere given by the given particle size measuring instrument corresponding to the response of the measured particle.


Note 2 The discrete particle counter gives the equivalent optical diameter.


2. 2. 3


Particle concentration


The number of particles in a unit volume of air.


2. 2. 4

Particle size distribution


The particle concentration of particles accumulated by particle size.


2. 2. 5

Ultrafine particle


Particles having an equivalent diameter of less than 0.1 μm.


2. 2. 6

Large particle macroparticle


Particles with an equivalent diameter greater than 5 μm.


2. 2. 7

Fiber fiber


(Length and width > particles with a ratio of not less than 10).


2. 3 descriptors


2. 3. 1


U descriptor U descriptor


The measured or specified concentration of air particles per cubic meter, including ultrafine particles.


Note: The U descriptor can be used as the upper limit of the average concentration of the sample points (or the upper confidence limit, which is determined by the number of sampling points in the clean room or clean area performance). Air cleanliness levels cannot be determined using U descriptors, but can be quoted individually or with cleanliness levels.


2. 3. 2

M descriptor M descriptor


The measured or specified concentration of large particles per cubic meter of air. The equivalent particle size in the M descriptor is related to the measurement method.


Note: The M descriptor can be used as the upper limit of the average concentration of the sample points (or the upper confidence limit, which is determined by the number of sampling points in the clean room or clean area performance). Air cleanliness levels cannot be determined using U descriptors, but can be quoted individually or with cleanliness levels.


2. 4 occupancy status


2. 4. 1


Empty state as-built


The facility has been built and operated but has no production equipment, materials and personnel status.


2. 4. 2

Static at-rest


The facility has been completed and the production equipment has been installed and operated on demand and agreed by the supplier, but there is no personnel status.


2. 4. 3


Dynamic operation


The facility operates in a prescribed manner, with a specified number of personnel working in an agreed manner.


2. 5 parties concerned


2. 5. 1


Demander customer


The agency or its agent that specifies the specific requirements of the clean room or clean area.


2. 5. 2


Supplier supplier


A facility that meets the requirements of a clean room or clean area.


Level 3


3. 1 occupied status


The cleanliness level of a clean room or clean area shall be determined according to one or several occupancy states, namely: “empty state”, “static”, “dynamic” (see 2.).


Note: The “empty state” test applies to newly built or newly renovated clean rooms or clean areas. After the “empty state” test is completed, the “static” or “dynamic” or both levels of detection should be performed.


3. 2 grade number


The air cleanliness level is indicated by the grade number N. The maximum allowable particle concentration for each particle size D of interest c. Determined by equation (1):


( 1 )


In the middle


Cn - one is greater than or equal to the maximum allowable concentration of particles of interest (expressed as the number of particles per cubic meter of air), and Cn is corrected to an integer not exceeding 3 significant digits;


N The number of the ISO grade, up to a maximum of 9. An intermediate level with a minimum increment of 0.1 can be set between each integer level of N;


D one is concerned with the particle size in micrometers (μm);


0. 1 One constant, in micrometers (μm).


Table 1 gives the integer level of air cleanliness and its corresponding particle size of interest and the allowable concentration of particles above. Figure A. 1 (see




  • Appendix A) illustrates the integer level. In the event of a dispute, the concentration Cn calculated by equation (1) shall prevail.

  •  

    3. Level 3 expression


    Expressing the cleanliness of the air in clean rooms and clean areas should include the following:


    a) the grade expressed in ISO N level;


    b) the corresponding occupancy status of the level;


    c) the particle size of interest and the corresponding concentration determined by equation (1), and each of the particle size thresholds is in the range of 0.1 μm to 5 μm.


    Example:


    ISO 4; dynamic attention to particle size O. 2 μm (2 370 / m3); 1 μm (83 pcs / m3).


    Both the acquirer and the supplier shall agree on one or more particle sizes of interest used in the concentration measurement.


    If the measured particle size of interest is more than one, the ratio of the larger of the two adjacent particle sizes (such as D,) to the smaller one of the day D, is not less than 1.5 times, namely:


    D1. 5 ×D1


    Level 4 confirmation


    4. Principle


    According to the agreement between the buyer and the supplier, the specified test is carried out, and the specified test results and test conditions are provided to verify that the facility meets the air cleanliness (ISO rating) requirements specified by the purchaser.


    4. 2 detection


    Appendix B gives the benchmark test method for the level of verification. Other methods with comparable accuracy can also be used. If no other test method is specified or agreed, the baseline test method should be used.


    Calibrated instruments should be used in the level test.


    4. 3 airborne particle concentration limits


    After completing the test according to 4. 2, calculate the average particle concentration and the 95% confidence limit (if applicable) according to the formula in Appendix C.


    The average particle concentration of the particle size of interest [see 3. 3c) calculated according to formula (C. 1) shall not exceed the concentration limit calculated according to equation (1) of 3. 2 .


    In addition, if the number of sampling points is not less than 2 and not more than 9, the 95% confidence limit calculated according to c. 3 shall not exceed the above.


    Calculated concentration limit.


    Note: Appendix D gives an example of level calculation.


    When particle concentration is used to determine consistency with grading limits, the same method should be used for concentration measurements for all particle sizes of interest.


    4. 4 test report


    Record and submit the results of each clean room and clean area in the form of a comprehensive report indicating whether the test results have reached the specified air cleanliness level.


    The test report should include the following:


    Name, address, date of inspection of the inspection agency;


    b) The national standard number of this part, namely GB/T 25915. 1 - 2010.


    c) clearly indicate the specific location of the clean room or clean area to be tested (use the adjacent area as a reference if necessary) and mark the specific coordinates of all sampling points;


    d) Standards specified for clean rooms or clean areas, including ISO grades, corresponding occupancy status, and particle size of interest;


    e) A detailed description of the test methods used, including special test conditions and deviations from the specified test methods; specifications of the test instrument, the latest calibration certificate of the instrument;


    f) Test results, including coordinates and particle concentration data for each sample point.


    Note 2 If the concentration of the ultra-fine or large particles is expressed in the description of Appendix E, the corresponding information should be included in the test report.


    Appendix A


    (informative appendix)


    Circle of cleanliness scale 1


    Figure A. l is a graphical representation of the air cleanliness level in Table 1 and is intended to be illustrative only. The ISO rating of Table 1 is shown by a straight line in the figure, and the straight line represents the level concentration limit corresponding to the particle size threshold. These limits are calculated according to equation (1) in 3. 2. The straight line in the figure is only an approximate representation of the grading limit. It is not possible to determine the limit and determine that the limit is still used.


    The solid points in the figure correspond to the maximum and minimum values of each ISO grade particle size threshold, so the grade line cannot extend beyond the solid point.


    The grade line does not represent the actual distribution of particle size in the clean room and clean area.


  • Appendix B


  • (Normative Appendix) Using Light Scattering Discrete Particle Counters


  • Determination of particle cleanliness level


  • B. 1 principle


  • The concentration of airborne particles greater than or equal to the particle size of interest is determined at a specified sampling point using a light scattering discrete particle counter.


  • B. 2 Instrument requirements


  • B. 2. 1 particle counter


  • Discrete Particle Counter (CDPC) is a light scattering measurement device that can display or record the number and particle size of discrete particles in the air: with particle size discrimination, the total particle concentration can be determined within the particle size range covered by the relevant cleanliness level. And with a suitable sampling system.


  • B. 2. 2 instrument calibration


  • The instrument shall have a valid calibration certificate; the calibration frequency and calibration method shall be in accordance with currently accepted standards and specifications.


  • B. 3 Pre-test conditions


  • B. 3. 1 Test preparation


  • Before testing, verify that all aspects of the overall operation of the clean room or clean area are normal and correct, and meet the performance requirements. Pre-test work can include things like z


  • a) air volume or wind speed detection;


  • b) air pressure difference detection;


  • c) air tightness detection;


  • d) Leak detection of the installed filter.


  • B. 3. 2 Settings for pre-testing instruments Set and align the instrument according to the manufacturer's instructions.


  • B. 4 sampling


  • B. 4. 1 Determine the sampling point position


  • B. 4. 1. 1 According to the formula CB. 1) Find the minimum number of sampling points:

  • In the middle


    NLL - the minimum number of sampling points (repaired to an integer);


    A area of clean room or clean area, in square meters ( m2 )


    Note: For horizontal unidirectional flow, area A can take a cross-sectional area perpendicular to the direction of the airflow.

    7

    B. 4. 1. 2

    Make sure that the sampling points are evenly distributed throughout the clean room or clean area and at the working surface height. If the purchaser specifies additional sampling points, the number and location of the new sampling points shall be specified. Note: Additional sampling points can be located at key locations derived from risk analysis.


    B. 4. 2 Determine the single sample size of each sampling point


    B. 4. 2. 1

    If the maximum particle concentration of the particle size is at the upper limit of the specified ISO level, collect enough air at each sampling point to detect no less than 20 particles.


    The single sample amount V of each sample point is determined by the formula <B. 2 ), :

  • Vs minimum sampling amount per sampling point (except for B. 4. 2. 2), the unit is liter (L);


  • Cn,m One-to-one correlation level The maximum concentration of particle size concentration limit, in units per cubic meter (m/m3)


  • 20 The number of particles that can be detected when the particle concentration is at the level limit.


  • Note: When the Vs value is large, the sampling time can be very long. The number of samples required and the sampling time can be reduced using the sequential sampling method (see Appendix F).


  • B. 4. 2. 2


  • The sampling amount of each sampling point shall not be less than 2 L, and the sampling time shall not be less than 1 min.



  • B. 4. 3 sampling procedures



  • B. 4. 3. 1


  • Set the particle counter CB. 2. 1) according to the manufacturer's instructions and the instrument calibration certificate.


  • B. 4. 3. 2


  • The sampling probe should point to the airflow. If the direction of the airflow at the sampling point is uncontrolled or unpredictable (for example, non-unidirectional flow), the inlet of the sampling probe should be vertically upward.


  • B. 4. 3. 3


  • At each sample point, sample at the minimum sample size determined by B.4.2.


  • B. 4. 3. 4


  • When only one sample point is required, CB. 4. D, then at least three samples are taken at that point.



  • B. 5 Record results



  • B. 5. 1 Average particle concentration at each sampling point



  • B. 5. 1. 1


  • Record the single sample concentration of each particle of interest (3.3) for the relevant air cleanliness level.


  • Note: The requirements of B.6.1 should be considered before calculating the 95% confidence limit.


  • B. 5. 1. 2


  • When there is only one sampling point, the average value of each of the particle size sampling data <B. 4. 3. 4 ) is calculated and recorded.


  • B. 5. 1. 3


  • When sampling 2 or more times at a sampling point, follow the procedure given in c. 2 from each sampling CB. 5. 1. 1)


  • Calculate the average concentration of particles for each particle of interest and record the results.



  • B. 5. Calculation requirements for 295% confidence ceiling (UCL)



  • B. 5. 2. 1


  • When there are more than one sampling point and less than 10, the average particle concentration of all points is obtained according to the procedure given in c.


  • CB. 5. 1) Calculate the total mean, standard deviation and 95% confidence limit.


  • B. 5. 2. 2


  • When there are only 1 or more sampling points, there is no need to calculate the 95% confidence limit.



  • B. 6 data analysis



  • B. 6. 1 grading requirements



  • If the average particle concentration measured at each sampling point and the 95% confidence limit calculated according to B. 5. 2 when applicable, do not exceed 3. 2


  • For the concentration limit determined by Chinese (1), the clean room or clean area is considered to have reached the specified air cleanliness level. If the test results fail to meet the specified air cleanliness level, a uniformly distributed sampling point can be added for testing. Recalculate the result


  • In addition to the data containing the new sample points, all data from the original sample points should be included. The recalculation of data, including new sampling points, is not modifiable.



  • B. 6. 2 Treatment of outliers



  • The calculation of the 95% confidence ceiling (UCL) may not meet the specified ISO rating. If the failure level is caused by a measurement error (due to operational errors or equipment abnormalities) or a single non-random outlier caused by abnormally low particle concentration (as the air of an individual measurement point is abnormally clean), the value may be disregarded. Condition is z


  • a) Data including all remaining sampling points when recalculating z


  • b) There are at least 3 measurements in the calculation;


  • c) The measured value not counted in the calculation shall not exceed one;


  • d) Record suspicious causes of measurement errors or low particle concentrations and obtain approval from both the supplier and the buyer.


  • Note: Depending on the nature of the application of the cleaned facility, the considerable difference in particle concentration at each sampling point may be reasonable or even intentional.


  • Appendix C


  • (normative appendix)


  • Statistical processing of particle concentration data


  • c. 1 General


  • In statistical analysis, only random errors (insufficient precision) are considered, and non-random errors (eg, deviations due to calibration errors) are not considered.

  • c. 395% confidence limit calculation method

  • Appendix E


  • (informative) Particle sizing and counting beyond the particle size threshold range




  • E. 1 principle



  • In some cases involving specific process requirements, the level of air cleanliness may be additionally specified in terms of particle concentrations outside the range of the grading particle size. The maximum allowable concentration of such particles and the corresponding detection method are agreed between the purchaser and the supplier. E. 2 (for U descriptors) and E. 3


  • Related detection methods and prescribed expressions are described in (for M descriptors).



  • E. 2 particles less than 0. 1 μm (ultrafine particles)-u descriptor



  • E. 2. 1 application



  • If it is necessary to assess the risk of contamination caused by particles smaller than 0.1 μm, sampling devices and measurement methods that meet the specific characteristics of such particles are used.


  • The number of sampling points should be determined in accordance with B.4.1. The minimum sampling amount should only be 2 L (B. 4. 2. 2).



  • E. 2. 2U descriptor expression



  • The U-descriptor can be used alone to describe the ultrafine particle concentration, or it can be used as a supplement to the air cleanliness level.


  • The U descriptor is represented by "U ( x ; y ) ", where z


  • z The maximum allowable concentration of ultrafine particles (expressed in air microparticles per cubic meter);


  • y - a particle size in microns, a suitable discrete particle counter has a particle count efficiency of 50% at this particle size point.


  • Example: particle size range of two to three 0. 01 μm, the maximum allowable ultrafine particle concentration of 140 000 / m3 can be expressed as "U040 000; 0. 01 μm)".


  • Note 1: IEST G-CC1002 gives a method for detecting the concentration of suspended particles less than 0.1 μm.


  • Note 2: If the U descriptor is used as a supplement to the air cleanliness level, the concentration of ultrafine particles (not less than the corresponding ISO grade)


  • 0. 1 μm particle concentration limit (number of particles per cubic meter).



  • E. 3 particles larger than 5 μm (large particles) - M descriptor



  • E. 3. 1 application



  • If it is necessary to assess the risk of contamination by particles larger than 5 μm, use sampling devices and measurement methods that meet the specific characteristics of such particles.


  • Large particles in airborne particles are normally released from the process environment, so the appropriate sampling device and measurement method should be determined based on the specific application. Factors to consider are: particle density, shape, volume, aerodynamics, etc. In addition, special attention may be required to specific components in the total suspended particles, such as fibers.


  • E. 3. 2M descriptor expression



  • The M descriptor can be quoted separately or as a supplement to the air cleanliness level. The M descriptor is represented by "M ( a ; b) ; c", where:


  • a The maximum allowable concentration of a large particle (expressed as the number of large particles per cubic meter of air);


  • B—the equivalent diameter (or diameter) (μm) corresponding to the specified large particle measurement method;


  • c One-to-one measurement method.


  • Note: If the sampled suspended particles contain fibers, a fiber mark can be added to the M descriptor, which is expressed as “M rape (a ; b) ; c”.


  • Example 1 :


  • If an aerosol time-of-flight particle counter is used and the measured particle aerodynamic diameter > S μm particle concentration is 10 000 / m3, the M descriptor is expressed as:


  • "M (1000; >5 μm); aerosol time-of-flight particle counter".


  • Example 2:


  • If the particles collected by the multi-stage impact sampler are measured and counted using a microscope, and the concentration of suspended particles in the particle size range of 10 μm - 20 μm is 1000/m3, the M descriptor is expressed as:


  • “M (1000; 10 μm -20 μm); multi-stage impact sampler, measuring particle size by microscope and counting fly


  • Note 2: IEST-G-CC1003] gives a method for detecting the concentration of suspended particles greater than 5 μm.


  • Note 3: If the M descriptor is used as a supplement to the air cleanliness level, the large particle concentration (a) should not be greater than the particle concentration limit of 5 μm (the number of particles per cubic meter) corresponding to the ISO grade.


  • Appendix F


  • (informative appendix) sequential sampling method


  • F. 1


  • Background and conditions


  • F. 1. 1 background


  • If the contamination level of the sampled air is significantly larger or significantly smaller than the particle concentration limit of the particle size of interest in the specified level, the sequential sampling method can usually greatly reduce the sampling amount and sampling time. Sequential sampling saves some work even when the concentration is close to the specified limit. Sequential sampling is most appropriate when air cleanliness is expected to be ISO 4 or cleaner.


  • Note 2 For details of the sequential sampling method, see IEST-G-CCl 004.


  • F. 1. 2 restrictions


  • The main limitations of the sequential sampling method are:


  • a) This method is only applicable to a total of 20 particles per sampling target for the particle size of interest at the specified level or concentration limit.


  • b) Each sample measurement is supplemented by monitoring and data analysis, which can be done automatically by the computer.

  •  c)由于序贯采样法降低了采样量,测出的粒子浓度不如常规采样法精确   

  • When air is sampled at a specified sampling point, the total number of particles being accumulated is continuously compared with the reference limit. The reference limit is a function of the ratio of the amount of air collected to the specified total. If the count being accumulated is less than the lower limit of the reference value corresponding to the amount of collected air, the sampled air is considered to meet the specified level or concentration limit, and sampling is terminated.


  • If the accumulated count is greater than the upper limit of the reference value corresponding to the amount of collected air, the sampled air does not meet the specified level or concentration limit, and sampling is terminated. As long as the count being accumulated is still between the upper and lower limits, the sampling will not stop and will accumulate to the complete sample.


  • C in Figure F. l is the measured count, which corresponds to E; E is the expected count, that is, the particle concentration of the particle of interest is at the specified limit, and can be collected in a complete single air sampling time. 20 Particle rate (sample size vs. sample time) When sampling, the count of particles can be taken.


  • Table F. l is another equivalent method. As shown in the table, the time at which the measured count C occurs is compared to the time at which the complete single sample is measured. If the counting occurs earlier than the progress time in the left column of the table, the collected air does not meet the specified limit. z If the counting occurs later than the progress time in the right column of the table, the collected air meets the specified limit. The particle's appearance time and the time limit in the table need to be compared up to 21 times.

  • F. 3 sampling procedure

  • F. 3. 1 Sequentially sampled reference values

  • There are two ways to compare the results of the process of data collection. The progressive data computer analysis method is better and recommended.

  • F. 3. 2 sampling comparison chart

  • Figure F.l shows the boundary lines set by equation (F.l) and (F. 2). These two boundary lines are truncated at E=20, which represents the time required to acquire a complete sample. C= 20 is the maximum qualified measured count.

  • This figure plots the correspondence between the observed count and the expected count when the particle concentration is accurately at the specified level. The increase in the expected count is accompanied by the passage of time, and E = 20 indicates the time required for the particle concentration to accumulate to a full sample amount at the level limit.

  • The procedure for sequential sampling according to Figure F. l is as follows:

  • As the sampling progresses, the particle count as a function of time is recorded and compared to the upper and lower edges of Figure F.1. If the measured cumulative count value exceeds the upper edge, the sampling of the sample point is terminated, indicating that the air does not meet the specified level limit. If the measured count value is lower than the lower line, the sampling of the sample point is terminated, indicating that the air meets the specified level limit. If the measured cumulative value is between the upper and lower edges, continue sampling.

  • If the total count does not exceed 20 at the end of the specified sampling time and does not exceed the upper line, it can be determined that the air has reached the level.

  • F. 3. 3 sampling comparison table

  • Table F. 1 gives another equivalent sequential sampling method in which the data is also calculated according to the equations C F. l) and C F. 2 ). The time t in the table is assigned 1. 000 0, which represents the time period for collecting a complete sample. The sample size, that is, the particle of interest in the air, is at its equivalent limit concentration, and the necessary amount of 20 particles is measured. The time values listed in the table are the progressive parts of the total accumulated time required for a complete sample.

  • The method of sequential sampling according to Table F. 1 is as follows:

  • As the sampling progresses, the particle count and the time of occurrence are recorded, and each time the count is actually compared with the two time bars shown in the table. If a measured count cumulative value occurs earlier than the progressive time indicated in the left time column of the table, the sampling is terminated and the reported air does not reach the specified level; if the cumulative value of a measured count occurs later than the right in the table The progress time indicated in the side time column terminates the sampling and reports that the air reaches the specified level. If the measured count accumulates continuously between the times indicated in the two time bars, continue sampling; if the 21 consecutive comparisons of the middle one count is earlier than the progressive time in the left column, the complete sample indicates that the air has reached the prescribed grade.

  • references

  • [1]IEST-G-CC1002 , Determina tion of the Concentra tion of Airborne Ultrafine Particles .

  • Mou nt Prospect , Illinois: Instit ute of Environmental Sciences and Technology (1999)

  • [2]IEST-G-CC1003 , Measurement of Airborne Macroparticles. Mount Prospect , Illinois : In­

  • stitute of Environmental Sciences and Technology (1999)

  • [3] IEST-G-CCl 004 , Sequential Sampling Plan for Use in Classification of the Particulate Cleanliness ofAir in Cleanrooms and Clean Zones. Mount Prospect , Illinois : Institute of Environmen­ tal Sciences andTechnology (1999)