GB/T 25915.17-2024 Cleanrooms and associated controlled environments - Part 17: Particle deposition rate applications
1 Scope
This document gives direction on the interpretation and application of the results of the measurement of particle deposition rate on one or more vulnerable surfaces in a cleanroom as part of a contamination control programme. It provides some instructions on how to influence the particle deposition rate and reduce the risk of particle contamination on vulnerable surfaces.
This document gives information on how a cleanroom user can use the particle deposition rate measurements to determine limits that can be set for macroparticles on vulnerable surfaces. It also gives a risk assessment method by which an acceptable risk of deposition of particles onto vulnerable surfaces in a cleanroom can be established and, when this is not achieved, methods that can be used to reduce the particle deposition rate.
An alternative to the particle deposition rate is the particle obscuration rate which determines the rate of increase of coverage of particles onto an area of surface over time. The particle obscuration rate can be used in an analogous way to the particle deposition rate and the required particle obscuration rate for a specified surface can be calculated and the risk from deposited particles reduced.
This document does not:
——provide a method to classify a cleanroom with respect to particle deposition rate or particle obscuration rate;
——directly consider the deposition of microbe-carrying particles, although they can be treated as particles;
——give any consideration to surface deposition by contact as, for example, when personnel touch a product and contamination is transferred.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 25915.3-2024 Cleanrooms and associated controlled environments - Part 3: Test methods (ISO 14644-3:2019, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
cleanroom
room within which the number concentration of airborne particles is controlled and classified, and which is designed, constructed and operated in a manner to control the introduction, generation and retention of particles inside the room
Note 1: The class of airborne particle concentration is specified.
Note 2: Levels of other cleanliness attributes such as chemical, viable or nanoscale concentrations in the air, and also surface cleanliness in terms of particle, nanoscale, chemical and viable concentrations might also be specified and controlled.
Note 3: Other relevant physical parameters might also be controlled as required, e.g. temperature, humidity, pressure, vibration and electrostatic.
[SOURCE: GB/T 25915.1-2021, 3.1.1]
3.2
clean zone
defined space within which the number concentration of airborne particles is controlled and classified, and which is constructed and operated in a manner to control the introduction, generation, and retention of contaminants inside the space
Note 1: The class of airborne particle concentration is specified.
Note 2: Levels of other cleanliness attributes such as chemical, viable or nanoscale concentrations in the air, and also surface cleanliness in terms of particle, nanoscale, chemical and viable concentrations might also be specified and controlled.
Note 3: A clean zone(s) can be a defined space within a cleanroom or might be achieved by a separative device. Such a device can be located inside or outside a cleanroom.
Note 4: Other relevant physical parameters might also be controlled as required, e.g. temperature, humidity, pressure, vibration and electrostatic.
[SOURCE: GB/T 25915.1-2021, 3.1.2]
3.3
critical particle size
smallest particle size (3.7) that negatively impacts on product or process quality
3.4
critical location
location where a vulnerable surface is exposed to particle contamination
3.5
operational
agreed condition where the cleanroom (3.1) or clean zone (3.2) is functioning in the specified manner, with equipment operating and with the specified number of personnel present
[SOURCE: GB/T 25915.1-2021, 3.3.3]
3.6
particle
minute piece of matter with defined physical boundaries
[SOURCE: GB/T 25915.1-2021, 3.2.1]
3.7
particle size
diameter of a sphere or the diameter of a sphere (circle) that encompasses a non-spherical particle, or an equivalent diameter
Note 1: The definition should be stated in relation to the measurement method.
Note 2: In ISO 14644-1, light scattering based detection is used. Other measurement methods yield different size definitions, See A.1 in Appendix A.
3.8
particle deposition rate; PDR
number of particles depositing onto a known surface area during a known time of exposure
Note: It is expressed in number per m2 per hour.
3.9
particle deposition rate level; PDRL
level of particle deposition rates (3.8) for a range of particle sizes (3.7)
3.10
particle obscuration rate; POR
rate of change of particle area coverage of a surface during time of exposure
3.11
test surface
surface of specific area and known surface cleanliness used to collect particles that deposit from the air in a specified time
Note 1: A test surface is used in this document to determine the particle deposition rate (3.8).
Note 2: A test surface can be a witness plate or an integral part of a measuring instrument.
3.12
vulnerable surface
surface whose functionality diminishes when particles larger than the critical size are present
3.13
witness plate
clean flat plate of a specified surface area used to collect particles that deposit from the air in a specified time
Note 1: A witness plate is exposed adjacent to a vulnerable surface (3.12) to obtain the particle deposition rate that occurs at that location.
Note 2: A witness plate is not normally part of a measuring instrument and, after exposure, the witness plate is taken to a measuring instrument for the counting and sizing of the particles deposited.
4 Symbols
The following symbols apply to this document.
A area of the silhouette of the observed particles (mm2)
a The area exposed to polluted air is measured in square meters (m2).
CD particle concentration in number of particles ≥D µm per m2
D particle size in micrometres
F particle obscuration rate
L particle deposition rate level
ND number of particles ≥D µm deposited onto a surface
O particle obscuration factor (in mm2•m-2)
RD particle deposition rate in number of particles ≥D µm per m2•h
t time of exposure
η efficiency of detection method
GB/T 25915.17-2024 Cleanrooms and associated controlled environments - Part 17: Particle deposition rate applications
1 Scope
This document gives direction on the interpretation and application of the results of the measurement of particle deposition rate on one or more vulnerable surfaces in a cleanroom as part of a contamination control programme. It provides some instructions on how to influence the particle deposition rate and reduce the risk of particle contamination on vulnerable surfaces.
This document gives information on how a cleanroom user can use the particle deposition rate measurements to determine limits that can be set for macroparticles on vulnerable surfaces. It also gives a risk assessment method by which an acceptable risk of deposition of particles onto vulnerable surfaces in a cleanroom can be established and, when this is not achieved, methods that can be used to reduce the particle deposition rate.
An alternative to the particle deposition rate is the particle obscuration rate which determines the rate of increase of coverage of particles onto an area of surface over time. The particle obscuration rate can be used in an analogous way to the particle deposition rate and the required particle obscuration rate for a specified surface can be calculated and the risk from deposited particles reduced.
This document does not:
——provide a method to classify a cleanroom with respect to particle deposition rate or particle obscuration rate;
——directly consider the deposition of microbe-carrying particles, although they can be treated as particles;
——give any consideration to surface deposition by contact as, for example, when personnel touch a product and contamination is transferred.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 25915.3-2024 Cleanrooms and associated controlled environments - Part 3: Test methods (ISO 14644-3:2019, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
cleanroom
room within which the number concentration of airborne particles is controlled and classified, and which is designed, constructed and operated in a manner to control the introduction, generation and retention of particles inside the room
Note 1: The class of airborne particle concentration is specified.
Note 2: Levels of other cleanliness attributes such as chemical, viable or nanoscale concentrations in the air, and also surface cleanliness in terms of particle, nanoscale, chemical and viable concentrations might also be specified and controlled.
Note 3: Other relevant physical parameters might also be controlled as required, e.g. temperature, humidity, pressure, vibration and electrostatic.
[SOURCE: GB/T 25915.1-2021, 3.1.1]
3.2
clean zone
defined space within which the number concentration of airborne particles is controlled and classified, and which is constructed and operated in a manner to control the introduction, generation, and retention of contaminants inside the space
Note 1: The class of airborne particle concentration is specified.
Note 2: Levels of other cleanliness attributes such as chemical, viable or nanoscale concentrations in the air, and also surface cleanliness in terms of particle, nanoscale, chemical and viable concentrations might also be specified and controlled.
Note 3: A clean zone(s) can be a defined space within a cleanroom or might be achieved by a separative device. Such a device can be located inside or outside a cleanroom.
Note 4: Other relevant physical parameters might also be controlled as required, e.g. temperature, humidity, pressure, vibration and electrostatic.
[SOURCE: GB/T 25915.1-2021, 3.1.2]
3.3
critical particle size
smallest particle size (3.7) that negatively impacts on product or process quality
3.4
critical location
location where a vulnerable surface is exposed to particle contamination
3.5
operational
agreed condition where the cleanroom (3.1) or clean zone (3.2) is functioning in the specified manner, with equipment operating and with the specified number of personnel present
[SOURCE: GB/T 25915.1-2021, 3.3.3]
3.6
particle
minute piece of matter with defined physical boundaries
[SOURCE: GB/T 25915.1-2021, 3.2.1]
3.7
particle size
diameter of a sphere or the diameter of a sphere (circle) that encompasses a non-spherical particle, or an equivalent diameter
Note 1: The definition should be stated in relation to the measurement method.
Note 2: In ISO 14644-1, light scattering based detection is used. Other measurement methods yield different size definitions, See A.1 in Appendix A.
3.8
particle deposition rate; PDR
number of particles depositing onto a known surface area during a known time of exposure
Note: It is expressed in number per m2 per hour.
3.9
particle deposition rate level; PDRL
level of particle deposition rates (3.8) for a range of particle sizes (3.7)
3.10
particle obscuration rate; POR
rate of change of particle area coverage of a surface during time of exposure
3.11
test surface
surface of specific area and known surface cleanliness used to collect particles that deposit from the air in a specified time
Note 1: A test surface is used in this document to determine the particle deposition rate (3.8).
Note 2: A test surface can be a witness plate or an integral part of a measuring instrument.
3.12
vulnerable surface
surface whose functionality diminishes when particles larger than the critical size are present
3.13
witness plate
clean flat plate of a specified surface area used to collect particles that deposit from the air in a specified time
Note 1: A witness plate is exposed adjacent to a vulnerable surface (3.12) to obtain the particle deposition rate that occurs at that location.
Note 2: A witness plate is not normally part of a measuring instrument and, after exposure, the witness plate is taken to a measuring instrument for the counting and sizing of the particles deposited.
4 Symbols
The following symbols apply to this document.
A area of the silhouette of the observed particles (mm2)
a The area exposed to polluted air is measured in square meters (m2).
CD particle concentration in number of particles ≥D µm per m2
D particle size in micrometres
F particle obscuration rate
L particle deposition rate level
ND number of particles ≥D µm deposited onto a surface
O particle obscuration factor (in mm2•m-2)
RD particle deposition rate in number of particles ≥D µm per m2•h
t time of exposure
η efficiency of detection method
