From the time of Swiss watchmakers, who used bell jars to prevent dust from falling on their timepieces, to the development of high-efficiency particulate air (HEPA) filters for atomic energy production, manufacturers have worked to limit airborne contamination in their production environments. Today, ISO standards still emphasize air filtration and air distribution requirements, but the science of cleanroom design has necessarily gone beyond air filtration to include all components of the room, including floors, walls and especially doors.
In modern pharmaceutical manufacturing facilities, for example, simply flushing cleanrooms with highly filtered air is of little effect if its doors do not appropriately contain and maintain the delicate balance of the cleanroom environment. Any particles, including hair and dust, provide microorganisms transport and a place to reproduce. So, whether it’s an ISO Class 5 or Class 7 (Class 100 or Class 10,000) cleanroom, the choice of door system can be a major factor in avoiding expensive cross-contamination and maintenance problems, as well as ensuring overall operating efficiency.
Although ISO 14644-4 provides direction on the basic elements of cleanroom design and construction, door system requirements are not specifically covered within cleanroom standards. As a result, before choosing a door solution, project engineers and designers must carefully investigate and consider a number of issues-including air pressure and sealing, cleanability, corrosion resistance, flexibility, security, and efficiency.
In bio/pharmaceutical cleanrooms, the right doors are first of all essential for maintaining appropriate room pressure and seal. With airflow levels and negative pressures in the hallway between suites, proper sealing to control predetermined air circulation rates, as well as to reduce airborne contamination, is mandatory.
Bio/pharmaceutical cleanroom designers are also constantly looking for door solutions that both maximize cleanability and stand up well to chemical treatment. For optimum cleanability, cleanroom doors should be manufactured with minimal ledges, crevices and angles. This inhibits dirt and bacteria from collecting easily and also makes it easier to withstand frequent cleaning. Surfaces should be nonshedding, nonporous and resistant to microbial and fungal growth (see Fig. 1). They should also be designed to tolerate consistent cleaning and sanitizing with a number of chemicals. Also, doors installed without drilling into the floor prevent additional accumulation of particles and the need for constant cleaning.
Historically, stainless-steel, aluminum and laminated wood products have been the most common materials used in door construction, but more recently, improvements in construction technology have made fiberglass doors a competitive choice. One recent study showed that today’s standard door materials deteriorate visibly over 30, 60 and 90 days when subjected to standard chemical solvents. The doors that fared best in the experiment were fiberglass doors manufactured much in the way fiberglass boats are created, using durable, seamless layers with no edges or grooves (see Fig. 2).
Corrosion problems go hand-in-hand with constant cleaning, especially with older door systems. Though it’s not uncommon for pharmaceutical cleanroom and lab areas to be outfitted with aluminum or painted-steel doors, eventually these aluminum doors will start to flake, deteriorate, and sometimes virtually dissolve after being exposed to toxic and severe cleaners. This long-term corrosion problem, coupled with cleanability issues, can cost manufacturers money in the long run. For areas that must truly be kept clean, aluminum doors may not be the best choice.
Corrodibility is not only a lurking problem on the door’s surface, but can also affect the door’s tracks. While galvanized tracks are a less expensive option, they are also corrodible. Stainless-steel tracks, on the other hand, offer longevity, durability and the ultraclean look companies and regulators prefer, especially if European standards are a consideration.
Besides cleanability and durability factors, cleanroom doors should offer various flexibility options to fit both personnel and process requirements. Having flexible door systems enables project engineers to outfit cleanrooms with interlocks, sliding panels, push plates or other activation devices, vision panels or magnetic locks.
A good cleanroom door system should support the use of vision panels for seeing obstacles before entrance. Vision panels are also beneficial for supervising personnel, monitoring manufacturing processes and maximizing natural light.
Doors should also be designed to implement card-key access, to fit owner-specified security system requirements and to incorporate door interlock systems. An interlock, sometimes referred to as an “airlock,” consists of two subsequent sets of doors, each opening separately with airspace between them. The functional concept of an interlock is to prevent two doors from being open at the same time, therefore thwarting air from filtering into one space directly from the other. Utilizing interlocks is not uncommon, especially in personnel entrances and exits, gowning and de-gowning areas, and material transfer airlocks in cleanroom environments.
Soft interlocks, the simplest and least effective type of interlock, are based strictly on protocol. This means each of the doors leading to the airspace in the interlock contains a vision panel. A person wishing to enter the airlock from either side looks through the window to see if the opposite door is open or closed. If the opposite door is open, protocol dictates that the person wait until the door is closed before entering the airlock. Sometimes, soft interlocks also incorporate lighted indicators or signs.
To prevent accidental or intentional breaching of the interlock protocol, hard interlock systems add automation into the equation. In this case, if an operator opens one door, a positions switch will be automatically activated causing the controller to interrupt the activation signal to the opposite door, preventing automatic operation. By preventing protocol from being violated, hard interlocks provide another level of insurance to the system.
With any hard interlock system, however, life safety and emergency ingress/egress issues must be considered. At a minimum, the airlock should include an emergency release device to prevent anyone from being trapped inside. It is also common to provide a means for the building management system to interface with an interlock controller. This ensures that all doors are unlocked in the event of a fire alarm, sprinkler-flow event or other user-defined occurence.
It is important to know that original swinging doors can be replaced with sliding doors that virtually “hug” the wall, requiring less operating space. A wide variety of sliding door systems – from single-slide to center-parting to telescoping types – simplify the retrofit design process. Replacement of an existing swing door does not necessarily require removal of the door frame. There are methods for encasing the old frame within the new frame, while maintaining the structural integrity, aesthetic appeal and cleanliness of the opening. This also reduces downtime and installation costs.
The ability to incorporate automation into the door operation is a key factor when designing a cleanroom environment. Both sliding and swinging doors can be fitted with automatic operators and “touchless” activation switches. Here, the doors are held open by a timer and close automatically after passage, which greatly helps in maintaining differential pressures.
Ultimately, new bio/pharmaceutical cleanroom designs are aimed at greater efficiency and cost savings. Practical cleanroom designs minimize HVAC requirements, reduce cleaning and maintenance costs, and effectively withstand the conditions in which they function.
By investigating cleanroom door products with an eye toward air seal, cleanability, corrosion, flexibility and security, designers can provide increased returns over the life of their doors and their cleanrooms as a whole. In addition, having the foresight to install doors that can be improved with interlocks and other features will minimize replacement and upgrade costs.
Having the appropriate cleanroom doors significantly contributes to the cleanliness of the critical environment. On the other hand, poorly selected door systems could generate particulates, increase cross-contamination and maintenance, and reduce efficiencies.