An elaboration on the Clean Room Construction for BOE OT B1-Project in Beijing, China
Paul Y. Construction Group has past experience in the construction of projects that are similar to the clean room requirements as stipulated in the present tender, although the extent and exact requirements are not the same. These project references included: 1. The “Jean-Marie Pharmacal Co., Ltd. Hong Kong” at Tai Po Industrial Estate,
2. The Cable Landing Station at Chung Hum Kok, Hong Kong (which
accommodated sensitive telecommunication equipments);
3. Data Centers at Goldman Sachs office located at Cheung Kong Center, Hong
Clean room is widely required in the micro-electronic manufacturing industry, in pharmaceutical field, in biotechnology arena. In this age of extensive use of nano-technology, the necessity of clean rooms is a must.
Inside a clean room there are various types of contamination including: 1. organic & inorganic matters,
4. gases & vapors.
The sources of these contaminants may be due to:
1. external natural sources,
2. external industrial sources,
4. equipment & facilities,
5. production materials and processes,
6. improper work practices etc.
The contamination pathway runs from the source, then transportation, then contact (with a sensitive area), and finally retention.
In the design and construction of clean rooms, we are much concerned about: 1. HVAC;
4. Reverse Osmosis/ Deionized water (RO/DI)
The commonly used standards for particulates are the US standard FED-STD-209D, or its metric revision 209E, which defined clean room classes. ISO14644-1 (1999) may also be used but not as common as 209D which has been used for quite sometime.
In FED-STD-209D, the Class Limits for particles per cu. ft of size equal or greater than the size shown in micrometers are listed below:
Class Measured Particle Size (micron)
0.1 0.2 0.3 0.5 5.0
1 35 7.5 3 1 NA
10 350 75 30 10 NA
100 NA 750 300 100 NA
1,000 NA NA NA 1,000 7
10,000 NA NA NA 10,000 70
100,000 NA NA NA 100,000 700
To create a clean area, there are some basic properties of the construction materials used for the floor, wall and false ceiling:
1. don’t outgas,
2. don’t generate particles,
3. mechanically & chemically stable,
4. could be cleaned.
As the contractor for the project, we will pay particular attention during the construction phase of the clean room. We understand that the clean room is no ordinary building project. It is a special place as soon as groundbreaking begins and not just when the keys are handed over. All actions and procedures will be reviewed with regard to micro-contamination aspects before they are carried out. The materials which will form walls, floor, and ceiling will be treated with respect as soon as they arrive on site. They will never be stored outside in the construction yard as they will inevitably be treated like all the other common building materials. Packaging on the materials will never be removed or torn until it is time to use the materials, and only under cover, out of the dirty outside air and damaging effects of sunlight. A general wipedown using special techniques will be adopted before and after installation. The pre-installation wipedown helps to prevent the trapping of contaminants in seals. After any cutting or drilling operation, the resealing operation will take place as soon as possible to prevent any long-term damage or deep contamination of the materials.
Once the flooring material is in, an operation which should be late in the construction schedule, construction employees will be gowned to some extent to help prevent damage to the floor and reduce ground-in contamination. Gowning means more than just overshoes. A Tyvek jumpsuit, booties, and a bouffant cap may be optimal at this stage, as contamination will come off working clothes. Any spills, filings, and so forth will be cleaned up immediately as they tend to become dispersed with time and are more difficult to clean up. Once the room has become a room (with walls, ceiling, and floor), even if the clean air supply has not yet been turned on, all nonessential operations will be prohibited. Prohibited are work on non-critical materials which will go outside the room, eating, smoking, and so forth. This may sound like overkill, but employee attitude toward the room is every bit as important as the
micro-contamination science aspect.
Once the clean air supply is turned on to the room, it is critical for construction workers to be appropriately gowned to protect the clean room and associated systems. The minimum attire should be whatever the operating apparel will be, except in the case of lower-class rooms. For rooms which will ultimately be class 10,000 or worse, a jumpsuit is still suggested, even if lesser protecting smocks will be used in production. The room should be as near to perfect as possible before sign-off and certification, and if this means that the contractors have to go overboard, then so be it. At this stage, the room will be cleaned each day, including wiping the walls and ceiling to remove the day’s construction dirt.
The completed room may be intrinsically clean, but the air put into it will most certainly be filthy unless we do something with it. What must be done is to clean it up by filtration and related techniques. The raw air should have been prefiltered to remove the bulk of the contamination, and precision filtering should be done immediately before the air enters the room.
As airflow is concerned, turbulence should be avoided, and laminar or unidirectional flow will be adopted, sometimes with pressurization to maintain a positive pressure.
Proper decontamination of equipment and materials that goes into the clean room is an important procedure. Most items destined for clean room use should be manufactured under clean conditions or cleaned by the manufacturer before they are packaged and shipped. A micro-contamination audit should be made of any vendor. Once the equipment or materials are ready for shipping, they must be packaged in a
minimum of two separate layers of wrapping. Take off the first layer of covering out on the loading dock or in an inside area off the dock. A clean staging area adjoining the clean room for the unpacking of equipment and supplies will be established.
The clean room procedures will be applied as soon as the building is “dried in”, i.e.
before any facility or utility systems or equipment are installed. From this point on, continuous cleaning is required, so that no dirt is trapped during construction to cause trouble later. Such cleaning should include: vacuum cleaning (with a brush) every surface, damp wash with free-rinsing, non-ionic detergent, rinsing with deionized water and a final wipe-down with “tack-cloth” prior to turning the facility in.
Clean rooms may be built by using traditional building construction techniques or specially developed prefabricated systems. The quality of construction of the clean room has a direct bearing on the amount of air leakage out, or into, the room and such leakage should be prevented. It is also necessary to avoid ledges and crevices where contamination may gather, as well as ensuring that the quality of the surface finish is such that undue particle generation can be avoided. Windows and doors will be constructed properly to avoid dirt traps and the junctions of finishes will also be ensured satisfactory. Air ducts will be constructed air tight and cleanable. Other services and utilities similarly require a satisfactory sealed entry to a room, or to a piece of equipment.
The materials and components used in the construction of a clean room will not be delivered to the construction site in a dirty state. As well as not being externally dirty, dirt should not be “built in” during manufacture, since over the lifetime of the clean
room this contamination could enter the clean room. All components and materials used in the construction of the clean room should be manufactured, packed, transported, stored and inspected, before use, to ensure their cleanliness.
During construction, measures will be taken to ensure that the contamination generated in the course of assembly and construction work is contained and removed, so as to limit undue contamination of surrounding areas. Appropriate means of containment may include the use of temporary screens and walls, and pressurization of critical zones, with provisional use of temporary “sacrificial” filters in the air
handling system(s). Such filters, installed to protect the clean environment and air handling systems from outside contaminants, and to permit their initial pressurization and operation, are intended to be removed and replaced by filters of the appropriate grade at the agreed stage or stages of start-up, before construction approval and
subsequent operational use of the installation.
Continual or frequent cleaning during construction and assembly should be planned, undertaken and controlled, with the aim of preventing undue build-up of contaminants in any part of the installation, and so facilitating the essential final cleaning before start-up.