High-performance doors, which have been used to increase the productivity of manufacturing facilities for decades, have now been designed for use in cleanroom facilities. These automated, high-speed doors combine airtight seals with fast opening and closing speeds to prevent contamination while increasing productivity.
Cleanrooms require precise control over specific environmental conditions.
The appropriate cleanroom class—as defined by the International Organization for Standardization (ISO) standard 14644—depends on the product, processing methods, and other conditions in the cleanroom. Semiconductor processes may require cleanrooms in Class 2, 1, or 0. Pharmaceutical manufacturers are primarily concerned with particles 0.5 mm and larger, and seek to maintain an ISO class of at least 5.
Once a cleanroom class is established, it must sustain the correct pressure level and particle count for that particular class. Testing demonstrates continuing compliance with the ISO class standards. Monitoring and maintenance systems, such as particle counters and airflow systems, are employed to help maintain cleanliness levels.
Constant pressure is very important, and tight seals on doors in cleanrooms are vital to pressure maintenance. The mechanical design of high-speed doors includes specialized sealing systems to minimize pressure loss and resist infiltration of external contaminates. A high-performance door designed specifically for cleanroom applications can create near-airtight seals that reduce air loss to a minimal 20 m3 per hour. It can also control particulates and leakage to meet stringent ISO standards.
Opening and closing speeds of up to 80 inches per seccond also help keep particle counts to ISO-specified minimums. Traditional sliding doors and overhead doors, which open at speeds of up to 12 inches per second, cannot provide the same amount of air separation as a high-performance cleanroom door.
Cleanrooms may also be subject to Good Manufacturing Practice (GMP) production and testing procedures. The U.S. Food and Drug Administration (FDA) enforces GMPs, and may conduct surprise inspections. For cleanrooms, GMPs stipulate that structural components should not release any particles, should have smooth surfaces that are easy to clean, and should have a maximum surface roughness of 0.8 mm.
High-speed doors can be outfitted with stainless steel side frames, bottom bars, header covers, and motor covers. Specialized high-performance clean doors will have limited recesses to meet GMP mandates. The doors can also be equipped with a “no touch” actuator: the user passes a hand in front of a sensor, and the door opens automatically and closes quickly. A touch-free door greatly reduces the spread of contaminates and makes sterile cleaning easier. The user can also set the timing of a high-speed door. Doors can be set to stay open a few seconds before they close automatically, or to close immediately after they open to prevent exposure to contamination.
High-performance door systems also include safe technology to protect employees. Photocells installed on high-speed doors can project infrared beams across the door. If these beams are interrupted while the door is closing, the door will automatically reverse to the open position.
The HVAC system in a cleanroom delivers an increased air supply to prevent harmful particles from settling. It also is used to help positively pressurize the cleanroom. In addition, high efficiency particular air (HEPA) filters are used for cleanrooms and may cover the entire ceiling.
When aligning a high-performance door system with specialized HVAC systems, the goal pressure difference, the size of the opening, and the desired ISO class should be considered.
When the HVAC and door system are properly aligned, the high-performance door will begin to alleviate some of the burden placed on hard-working HVAC systems. The fast speeds that limit air exchange also reduce wear and tear on the filters, allowing the cleanroom to operate more efficiently.
An airlock consists of multiple doors or curtains for additional control over airflow patterns. In cleanroom environments, airlocks are utilized when moving equipment, materials, or personnel in and out of various cleanroom spaces. When multiple products are processed in one facility, airlocks prevent cross-contamination between two areas served by two different HVAC systems. The airlock system also serves to minimize the change in pressure between adjoining cleanroom spaces. The design of the airlock depends on the product, processes, and materials that are transported between areas.
High-performance doors are ideal for this space because of their reliable automatic operation and effective air tightness, which limits air loss within the lock. In addition, high-performance doors can be equipped with light-emitting diode (LED) technology that will visually display the status of this controlled passageway. If the first door in the lock is opened, the LED on the second door will turn red; operation of the second door is prohibited. When the first door is fully closed, the LED on the second door will turn green, and the second door will become operational.
This strict “traffic light” system assures that the two airtight doors in a lock never open simultaneously, a factor that is crucial in sensitive cleanroom environments.
Clear door panels are another beneficial design feature of high-speed doors. The added visibility helps optimize the flow between separate areas. In some processing facilities, there may be frequent traffic as workers move materials back and forth. These fast-moving transparent doors let workers move about quickly, easily, and safely.
High-speed doors feature a variety of safety devices to protect both workers and products. In addition to traditional safety measures such as infrared beams and impact-sensitive door bottom edges, a high performance door can be equipped with an uninterruptable power supply. If there is a power failure, the door will continue to operate, protecting personnel while preventing any risk of contamination.
New technology such as high-performance door systems will be key to increasing productivity in cleanrooms, while maintaining stringent cleanliness requirements. Not only do these doors help facilities meet and sustain ISO and GMP requirements, high-performance door systems also can advance the design of the cleanroom, help increase efficiency, and improve the safety of workers and products.
Dawn V. Brown is a marketing consultant for Assa Abloy Entrance Systems, High Performance Door Solutions. She has experience as a researcher and technical writer. Contact: firstname.lastname@example.org.
This article appeared in the September 2012 issue of Controlled Environments.