Make protocols the top priority for ISO 7 cleanrooms
Designs can only be successful if the proper actions are taken to maintain cleanliness levels
By Thomas E. Hansz, AIA, Facility Planning & Resources, Inc.
Last month’s article on ISO 5 cleanrooms discussed the importance of establishing and maintaining the appropriate level of contamination control in a cleanroom. This holds true of cleanroom design at any level of cleanliness, and requires a close relationship between the cleanroom design process and the development of operational protocols. This is critical for whatever industry the cleanroom is intended to support.
Sticking to a cleanliness program
As cleanroom consultants, we spend a considerable amount of time in our clients’ facilities, documenting existing conditions and observ-ing operations. On one such opportunity, we were asked to correct a cleanroom design that was producing unacceptably high particle counts in an ISO 7 level medical device packaging line. During our investi-gation, we discovered that the cleanroom was properly designed and adequately equipped; however, one day standing outside the cleanroom, we soon discovered the real problem with the client’s contamination control. We watched as a cleanroom technician walked out of the gown room, proceeded down the hall to a vending machine, purchased a candy bar, and returned to the cleanroom, fully gowned. As we later interviewed the cleanroom staff, it was plain to see that operational protocols existed but were never enforced.
Figure 1. Proper gowning is the first step toward maintaining cleanroom protocols. Photo courtesy of Facility Planning & Resources, Inc.
Contrast this to some operators who run what I will describe as “very basic” cleanrooms, yet achieve exceptionally low particle counts well below the cleanliness levels for which they were designed. In these cases, each cleanroom is operated in strict accordance to the established protocols, and they undergo daily vacuuming and cleaning. All cleanroom employees are focused on their work responsibilities, which includes maintaining the cleanliness level of their work environment.
One client has given the person in charge of daily cleanroom maintenance the authority to remove anyone from the cleanroom who does not follow the protocols or is not properly gowned. Dubbed the “Cleanroom Marshal,” he related with pride the time he stopped the president of the company and made him return to the gown room to put on a face mask, which was required for all persons with facial hair. It is no surprise to see that the facility’s production reject rates were so very low. Attention to cleanliness positively affects the bottom line.
Nanotechnology and industry applications
As discoveries in nanotechnology are applied to more and more industries and academic research, ISO 7 level cleanrooms (as well as ISO 8 and ISO 9) are becoming more prevalent. Once found only in integrated circuit assembly and test facilities and in pharmaceutical facilities, ISO 7 cleanrooms are commonplace throughout industrial sectors such as biomedical, biotechnology, medical device, automotive, advanced materials, metallurgical, and optical devices. Universities and colleges are also adding ISO 7 cleanrooms to support research programs in chemistry, biology, biochemistry, and biomedical applications.
Cleanroom entry and exit
Two of the more common mistakes in ISO 7 cleanrooms are the under-sizing of the gown room and the absence of supporting intermediate clean spaces. Cleanroom personnel should enter through a gown room that affords sufficient space for individuals to enter, gown up, and prepare to enter the cleanroom concurrently with individuals leaving and de-gowning. Airlocks should be placed between the gown room and the cleanroom as a final measure for eliminating particles from entering the controlled space. The air shower is characterized by a high velocity (6,000 fpm+) air stream scouring the garment of the person passing through into the cleanroom. In high traffic situations, an air shower tunnel may be used to accommodate a stream of people rather than a one-at-a-time air shower. When leaving the cleanroom, a separate door into the gown room is required because the air lock should only be used for entering the cleanroom.
Supporting intermediate spaces include pass-throughs and wipe-down rooms. Pass-throughs are installed in the wall separating the cleanroom from a non-controlled space, allowing materials, chemicals, and other items to enter the cleanroom without going through the gown room. Similarly, separate pass-throughs are required for finished work and wastes leaving the cleanroom. Pass-throughs have interlocking doors to prevent both doors from being opened at the same time. Airlock can vary in size from very small units–12 inches in height, width, and depth–to those large enough to accommodate lab carts. Special protocols should be developed as to the preparation and containment of items entering through a pass-through.
Figure 2. Flexible cleanrooms require designing in balanced airflow patterns. Photo courtesy of Facility Planning & Resources, Inc.
Wipe-down rooms for equipment and materials to be unpacked and wiped clean are necessary where these items frequently enter the cleanroom. Although such spaces may seem like a luxury, their use can often prevent the cleanroom from becoming contaminated and requiring a thorough cleaning and reclassification. The principle at work is what we described last month as “islands of cleanliness.” Regardless of the cleanliness level, if the principle is followed and maintained, the chances of successful contamination control are very high.
Let’s look at some of the basic physical components of ISO 7 cleanrooms: walls, ceilings, floors, airflow structures, and lighting.
Cleanroom wall and ceiling components
Class 10,000 cleanroom wall systems using vinyl-covered gypsum wallboard on steel studs have been around for years and continue to be quite popular due to their relatively low cost. However, due to the composition of the panel itself, they are not recommended for installations that require reconfiguration or frequent change-out of equipment or utilities. Many of the manufacturers of such wall systems proudly refer to the fact that their panels conform to Federal Standard 209 D, which has been superseded twice in the past 20 years.
In ISO 5 level and above cleanrooms, powder coated, aluminum honeycomb wall systems have been an industry standard for decades; they are anti-static, they do not shed particles, and they do not outgas. They offer other advantages as well: They are non-combustible, lightweight, and easily relocatable. Where these considerations are important, they make excellent wall systems for ISO 7 cleanrooms.
Life science and pharmaceutical operations usually require wall systems that are thoroughly washed on a regular basis. The finished surface must withstand cleaning and sanitization with various chemicals that resist fungal and microbial growth. Another consideration for life science and pharmaceutical wall systems is to have a curved base where the wall meets the floor. This follows current Good Manufacturing Practice requirements for maintaining aseptic and/or sterile environmental conditions.
For ISO 7 cleanrooms, composite wall systems are available in a variety of options. Wall panels can have interior cores of aluminum honeycomb, paper honeycomb, expanded polystyrene, or isocyanurate insulation. In addition to the powder coated aluminum surfaces, many cleanroom wall manufacturers also offer high pressure laminates, melamine, vinyl, stainless steel, and PVC. It is recommended that the cleanroom ceiling panels be of the same finish as the wall panels. Either the ceiling panel or the ceiling suspension system needs to be capable of supporting the fire sprinkler system. With so many options, it is important to select a wall and ceiling system that supports the work, as well as complying with federal regulations and other requirements.
Windows are another consideration for the cleanroom wall system. Windows should be flush to the wall on the clean side to prevent accumulation of particles. Designs are available for flush windows on both sides of the wall, a particularly useful feature for windows between adjacent clean spaces. Whether for a corporate, institutional, or academic cleanroom, window placement is important for visual safety, permitting supervision from the outside. Windows are also important for supporting marketing tours that invariably include looking into the cleanroom.
Floors on grade are frequently covered with a high-solids epoxy finish applied to an appropriately prepared concrete surface. Vinyl tiles and vinyl sheeting, with standard, static dissipative, or conductive characteristics, are also used, depending on the application. Whether to use a raised floor or not for your cleanroom depends upon factors such as the volume of recirculating airflow, the need for under-floor utilities and/or exhausts, and the criticality of regular cleaning.
The table of airflow guidelines (Table 1) relates the cleanliness class to a range of air change rates that increase as the ISO cleanliness class becomes more stringent. The table presents ranges of values to underline the notion that this is not an exact science. The final selection of air changes per hour is based on the process to be protected, the number of people working in the cleanroom, the activity and movement of those people, and the ratio of acceptable yield of finished work.
For ISO 7 cleanrooms, notice that the two variables in the chart are the airflow velocity and the number of air changes per hour. Other factors that need to be taken into account are the uniformity of the airflow pattern within the room and the configuration of the room itself. So to successfully provide the ISO 7 level of cleanliness, the HEPA filter coverage can vary from the 20 percent recommendation. It is important to remember that the following rates are recommendations, not hard and fast rules. We have been very successful in building
ISO 7 cleanrooms with varying percentages of filter coverage.
FIgure 3. Floor air returns should be strategically placed near major pieces of equipment. Photo courtesy of Facility Planning & Resources, Inc.
It should be mentioned that the design of the air pattern relies on careful filter placement in the ceiling as well as careful air return placement at the cleanroom floor. It is important that the cleanroom designer fully understand the process within the cleanroom to ensure that an optimum design is created at the lowest cost.
The temperature to be maintained in the cleanroom is driven by either comfort or by the process. Comfort in an ISO 7 cleanroom can generally be met by maintaining a temperature of 72??F (??2??) in facilities where lab coats or smocks, shoe covers, and hair bouffants are appropriate. In the more critical ISO 7 cleanrooms, full “bunny” suits may be required. In such cases, a temperature specification of 68??F (??2??) would be appropriate for maintaining personal comfort. Earlier, I mentioned some experiences with ISO 7 cleanrooms that had successful results with maintaining low particle counts on a continuing basis. In several of these cleanrooms, the personnel wore full bunny suits.
Care should be taken when specifying temperature values and tolerances as a result of a perceived need by the process. High or low temperature values can be costly to maintain. Even more costly can be the need to hold a tight tolerance when it isn’t necessary. A ??1??F tolerance is more costly than a ??2??F tolerance. A ??0.5??F tolerance is exponentially more costly. This becomes even more evident if the need is to maintain a tight tolerance throughout the entire cleanroom, 24 hours per day, year round with widely fluctuating outside air conditions and process equipment heat generation. High first cost, high operating cost, and many “out of spec” periods can result.
A common misperception by some cleanroom managers is that temperature can always be controlled by changing the flow of air. This is not always accurate. As the airflow increases, the effect of loads in the space decreases. However, the effect of the supply air temperature variations increases.
Many of the remarks relative to temperature also apply to humidity control. The selected value and tolerance should be realistic to the application. Comfort can be realized over a range of 30 to 65 percent RH if the temperature is held at a comfortable level. The only reason for a tighter tolerance is if the process requires it. In most areas, both humidification and dehumidification equipment must be incorporated into the mechanical system if a tolerance such as ??5 percent RH is required. If a tolerance of ??2 percent RH is required, particular care must be taken with the controls as well as the means of adding and removing moisture from the air.
Controlling pressure differential between clean and uncontrolled spaces is another important piece of cleanroom management. Typically, the pressure of the most stringent space is the highest. It is maintained at a pressure of 0.02 inches of water column (in.w.c.) above an adjacent less stringent clean space, or 0.05 in.w.c. above an adjacent unrated space. Higher differentials will work as well; however, if it gets too high, noise problems develop and there can be difficulty in opening doors or keeping doors closed. It also contributes to higher operating cost.
Using fan filter units
We have noticed over the years that a majority of ISO 7 cleanrooms are planned to be developed in existing buildings. For industrial or production facilities, this usually presents few problems. Where we have the greater number of restrictions is in academic research cleanrooms. Many times, the available space has a dimension from the floor to the underside of floor structure greater than or around 13 ft. Even with a clear height of 15 ft., the installation of makeup air ducts and recirculating air has required much more space than what is available. Such a space requires the use of fan filter units (FFUs) in place of a recirculating air unit and either ducted or plenum air supply.
FIgure 4. The cleanroom should be cleaned daily during the final stages of construction. Photo courtesy of Facility Planning & Resources, Inc.
However, it is not always the height restriction that guides us to use FFUs for the filtered recirculating air. A general rule of thumb is with less than 20 filters, a fan-powered HEPA (FFU) design is less expensive than a more conventional ducted supply system. Utilizing a conditioned supply air plenum and fan-powered modules allows for the use of standard, off-the-shelf air conditioning equipment and conventional ductwork, which need not be sealed for pressurization and, in turn, is less costly to fabricate and install.
A lot of highly detailed work is done in cleanrooms, and there is a tendency to specify high lighting levels (i.e. 100 foot-candles [1,000 lux]), with resulting high energy input and high contribution to cooling load. Use of task lighting for fine work and a general specification of 70 to 80 foot-candles lowers the cooling load and reduces cost by reducing the number of lighting fixtures. We have found that in ISO 7 cleanrooms, a ceiling system that incorporates lighting into the ceiling grid using T-5 lamps provides ample, uniform lighting as well as a high-tech image that supports the marketing aspects of cleanroom ownership.
Throughout this article, and the previous piece, much of what has been said concerning ISO 7 and ISO 5 cleanrooms can be applied to other levels of contamination control. What is important is what cleanroom purpose–production or research–is the basis for the design and that significant attention has been given to how that process may change over time.
Thomas E. Hansz, AIA, is founder of Facility Planning & Resources, Inc., the director of advanced technology projects for Flad & Associates, and a member of the CleanRooms editorial advisory board.