1、 Institute of Environmental Sciences and Technology IEST-RP-CC044.1 Contamination Control Division Recommended Practice 044.1 Vacuum Cleaning Systems for Use in Cleanrooms and Other Controlled Environments 1827 Walden Office Square, Suite 400 Schaumburg, IL 60173 Phone: (847) 981-0100 Fax: (847) 981
2、-4130 E-mail: informationiest.org Web: www.iest.org 2 IEST 2017 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-CC044.1 IEST-RP-CC044.1 Institute of Environmental Sciences and Technology IEST 2017 All rights reserved 3 This Recommended Practice was prepared by and is u
3、nder the jurisdiction of Working Group 044 of the IEST Contamination Control Division (WG-CC044). The following WG voting members contributed to the development of this edition of this Recommended Practice. Roger Diener, RBD Associates WG-CC044 Chair Taguhi Arakelian, Jet Propulsion Laboratory WG-CC
4、044 Co-chair Eugene Bryan, Milholland able to ignite or cause ignition. Laskin nozzle A nozzle used as part of a system to generate a polydisperse aerosol from a liquid, such as PAO, and which uses a source of compressed gas in accordance with IEST-RP-CC013. multistage filtration A process involving
5、 removal of particles from air flowing through a series of filter elements of increasing filtration efficiency. nanoscale Approximately 1 nm to 100 nm (1 nanometer = 1 billionth of a meter) size range of materials and structures. outgassing The process by which a solid material releases or emits a g
6、as or vapor. particle A minute piece of solid matter with defined physical boundaries, typically smaller than 100 m in diameter. polydisperse A lognormal aerosol distribution having a geometric standard deviation greater than 1.25. Venturi effect (as applicable to this RP) The method used to create
7、a vacuum by passing high-velocity air across an orifice (Venturi), thereby creating a low pressure (vacuum). 10 IEST 2017 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-CC044.1 3.2 Abbreviations CDA Compressed, dry air. DEHS (DOS) Di(2-ethylhexyl) sebacate (Dioctyl se
8、bacate) an insoluble, colorless, odorless liquid, suitable for producing aerosol droplets that can be used for testing air cleanliness levels in cleanrooms. EMI Electromagnetic interference (see also RFI). ESA Electrostatic attractionthe property of oppositely charged materials to be attracted to ea
9、ch other. ESD Electrostatic dischargean arc or sudden flow of electricity between two electrically charged objects, that can result in physical or electrical damage to either or both objects. HEPA High-efficiency particulate air (filter)a filter that that is 99.97% efficient in filtering 0.3-m parti
10、cles. NRTL Nationally recognized test laboratory. PAO Poly-alpha-olefina highly purified 4-cSt synthetic oil, which, when converted to an aerosol by an airborne particle generator, acts as a controlled particle challenge for determining air cleanliness levels in cleanrooms. (Refer to IEST-RP-CC034 f
11、or further details.) PPE Personal protective equipmentequipment or apparel used or worn by personnel for protection from risk to personal safety. PSL polystyrene latex (microspheres)solid, inert polymeric spheres produced as an aerosol by an airborne particle generator. PTFE Polytetrafluoroethylenea
12、 synthetic fluoropolymer of tetrafluoroethylene generally used for its chemical resistance and non-stick properties. RFI Radio-frequency interferencean external disturbance in the radio frequency spectrum that affects the designed operation of an electrical circuit by electromagnetic induction, elec
13、trostatic coupling, or conduction. ULPA Ultra-low penetration air (filter)a filter that is 99.999% efficient in filtering 0.3-m particles. 4 BACKGROUND AND PURPOSE 4.1 General Vacuum cleaning plays an important role in the general contamination control program for any cleanroom or controlled environ
14、ment by removing contaminants, typically larger than 10 m. Proper vacuum cleaning followed by additional wiping techniques, as recommended in IEST-RP-CC018, can result in extremely clean surfaces. Vacuum cleaning systems dedicated to cleanroom applications should be specifically designed, operated,
15、maintained, and tested for that purpose; otherwise, contamination can unknowingly be generated and spread through the cleanroom. Risks and limitations associated with portable and central (built-in) vacuum cleaning systems should be carefully considered. Application of the principles provided by thi
16、s RP will assist in making an informed decision in the selection and use of the most appropriate equipment for each application. This RP discusses the fundamental requirements for vacuum cleaning systems to perform effectively in cleanrooms and controlled environments of all types. Preventive mainte
17、nance fundamentals will also be introduced. Vacuum IEST-RP-CC044.1 Institute of Environmental Sciences and Technology IEST 2017 All rights reserved 11 cleaning systems should be tested in operation to verify they will not be a source of contamination when used in the cleanroom. 4.2 Vacuum cleaner ba
18、sics A vacuum cleaning system consists of a vacuum generator or motor that provides a means of suction through a hose and vacuum tool, which can be used to remove contamination from a surface. Such contamination may include visible debris, smaller fibers, and particles. High-velocity, negative air p
19、ressure present at the pickup tool collects the particulate contamination and propels it through a hose so it can be trapped in a collection chamber. The location of the chamber and motor determines whether the vacuum cleaning system is portable or central. Portable and central vacuum cleaning syste
20、ms each have inherent strengths, limitations, and risks that should be considered during the selection process. An incomplete assessment of these and other requirements can have a negative impact on the products produced in the cleanroom environment. Selection criteria are provided in subsequent sec
21、tions. 4.3 Suitability of vacuum cleaners for use in cleanrooms The ISO 14644 series of cleanroom standards provides guidance on a wide variety of cleanroom topics. ISO 14644-1:2015 provides the limits for specifying the cleanliness class of the air in a cleanroom, using a numerical scale based on t
22、he number of particles counted in a sampled volume of air. The air cleanliness class is the fundamental guide for defining the cleanliness of air inside a cleanroom. NOTE: The ISO Class designation (e.g., ISO Class 5) pertains to air cleanliness and should not be used to describe the relative cleanl
23、iness of a vacuum cleaner, equipment, or anything else used in the cleanroom. To properly address the control of contamination inside a cleanroom, equipment should be demonstrated to be suitable for operations, based on the specified cleanliness of the room environment. ISO 14644-14 provides a metho
24、d for determining the suitability of equipment for use in cleanrooms by measuring airborne particle concentrations resulting from the use of the equipment compared with the specified ISO Class for air in the cleanroom. This information is useful for assessing the particle generation by equipment suc
25、h as vacuum cleaners. Manufacturers are encouraged to test and provide such information to aid users in the process of selecting cleanroom vacuum cleaners. 5 PORTABLE VACUUM CLEANING SYSTEMS 5.1 Overview Portable vacuum cleaning systems used for dry pickup are self-contained and should operate entir
26、ely within the cleanroom environment. Materials that may be present in the air collected by the suction tool include particles, fibers, and other debris. Gross contamination is trapped in the intake module collection chamber. Smaller particles are trapped in a separation module with multiple stages
27、of filtration as the air continues to flow to and through the vacuum-producing motor module. This process also helps to extend vacuum cleaner life and prevent premature blocking of the final filter. Air exiting the motor module contains ultrafine and motor-generated particles that should be filtered
28、 before exhaust air is expelled. Filter elements should be designed and constructed to withstand the rigors of mobile use. Cleanroom requirements dictate that all air exhausted from a vacuum cleaning system not negatively impact the cleanliness specifications for the cleanroom. Exhaust air cleanline
29、ss and turbulence should be controlled. A HEPA or ULPA filter is required to trap these particles and reduce exhaust air turbulence to minimize risks for the cleanroom. A testing procedure should be adopted to verify that the system is not leaking or emitting airborne particles between maintenance c
30、ycles or after maintenance is performed. Selection of the proper type of vacuum-producing motor depends on the application. See Appendix B for additional details on the various motor types for portable vacuum cleaners. A detailed discussion of basic vacuum cleaner functional elements and filtration
31、(illustrated in Figure 1) is provided in subsequent sections. 12 IEST 2017 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-CC044.1 Figure 1Basic functional elements and filtration stages in portable vacuum cleaners. Each component used in the vacuum cleaner system may
32、have characteristics critical to its function. These characteristics may include, but are not limited to, ESD safety, grounding, static conductivity, food grade, cleanability, sterilization, and acid resistance. 5.2 Filtration System 5.2.1 Multistage filtration system The initial stage of filtration
33、 typically involves removal of gross particles and debris with a filter bag in the collection chamber. This simplifies the task of emptying and reduces the related mess. Additional progressively finer filter media can be employed between the collection module and the motor module to further clean th
34、e air, thus reducing friction and buildup in the motor. The filter element(s) in the fine separation chamber should conform to the requirements for prefilters in accordance with IEST-RP-CC002. Air drawn into the intake port of the vacuum cleaner is contained within the system and filtered prior to b
35、eing expelled from the exhaust port. Debris and particles picked up by vacuuming procedures are collected in a manner that enables removal without compromising internal filtration or motor elements. All air exiting the system is expelled through a HEPA or ULPA filter. Filter design and performance s
36、hould be specified in accordance with IEST-RP-CC001. For more information on multistage filtration, see Appendix C. 5.2.2 Exhaust airflow filtration HEPA or ULPA filters provide the final level of particle filtration for all air that exits the vacuum cleaner. The exhaust outlet should be well below
37、and directed away from work surfaces. Disturbance of the room airflow is reduced through diffused air exhaust. If it is critical to remove the exhausted air from the cleanroom, a central vacuum system should be considered. 5.3. Components 5.3.1 Vacuum generator (motor) Portable vacuum cleaners have
38、internal motors that produce the vacuum. Motors should be designed to minimize noise and vibration. Thermal overload protection helps prevent damage to plastic housings. General purpose cleanroom vacuum cleaners: o Commonly use universal flow-through discharge motors with carbon brushes IEST-RP-CC04
39、4.1 Institute of Environmental Sciences and Technology IEST 2017 All rights reserved 13 o Require a HEPA or ULPA exhaust filter for flow-through and motor generated particles Hazardous or explosion-proof vacuum cleaners: o Commonly use motors that are completely sealed to prevent airflow through and
40、 out of the vacuum o Require a HEPA or ULPA exhaust filter for flow-through and motor generated particles for hazardous or explosion-proof vacuum cleaners Liquid (wet) vacuum cleaners: o Commonly use bypass-discharge motors o Require separate HEPA or ULPA filters, one for the separation module and o
41、ne for the motor module See Appendix B for additional details concerning vacuum-producing motors. 5.3.2 System housings Portable vacuum cleaners are comprised of functional modules within a single housing or modular housings joined together to form a canister. Typical canister housing surfaces are c
42、omposed of many materials, including: stainless steel anodized aluminum thermoplastics powder-coating polytetrafluoroethylene (PTFE) and other coatings a) Materials Materials used for vacuum cleaner canisters or housings should be compatible with the operations or special requirements of the cleanro
43、om. Outer and inner surfaces of the canister housing should: Be cleanable to be essentially free of particles and residue Be compatible with disinfectants or withstand sterilization procedures, if required Limit the buildup and propagation of electrostatic effects (ESD, ESA, EMI) that can result in
44、contamination of products and processes or disrupt other critical equipment Limit outgassing, which can contaminate the cleanroom environment and products or processes being produced in the cleanroom b) Surfaces Special precautions may be required for the collection of liquids or materials that may
45、outgas. Interior surfaces should not be degraded by materials that may be collected inside. c) Component enclosure The internal components of the vacuum cleaner should be adequately secured within the housing to minimize the possibility of an accidental discharge into the cleanroom environment. Some
46、 applications may require special tamperproof locking features to ensure that the contents can be removed only by authorized personnel, in order to: Avoid leaks due to improper assembly Avoid hazardous contamination Reclaim value content such as precious metals d) Connection considerations 14 IEST 2
47、017 All rights reserved Institute of Environmental Sciences and Technology IEST-RP-CC044.1 All connections between accessories and segments of the vacuum cleaner housing modules should be tightly fitted, and all polymer seals, latches, and fasteners should be intact and effective. Uncontrolled, inco
48、ming or outgoing air can spread unwanted contamination or create unwanted air turbulence. Either situation can cause contaminants to become airborne and spread at random throughout the cleanroom. Leakage between internal component chambers should also be minimized to prevent premature failure of the
49、 filter elements or the motor. 5.3.3 Collection chamber The majority of waste, gross particles, and debris is trapped in the collection chamber. The collection chamber is most often accessed for service, during which the chamber is emptied of dust and dirt to attain maximum suction and airflow. The chamber should be easily accessible to avoid unit damage during those activities. When the collection chamber reaches its collection capacity, the vacuum cleaner should be removed from service and emptied to avoid risk to the vacuum
