Cleanrooms - Classifications and Exposures

Steve Morkovsky
August 14, 2012

Executive Summary

Cleanrooms are typically rooms where production or manufacturing processes take place that require an exceptionally clean area to ensure contamination levels do not adversely affect the process and/or the product. Cleanrooms are classified according to how clean the room has to be, which is determined by the product or process. These classifications essentially refer to particulate count levels that are airborne relative to particle size. Basically, the lower the number, the cleaner the room.1

Many processes taking place in cleanrooms use hazardous gasses and/or liquids that can cause catastrophic results if things go wrong. Simple spills or leaks can result in emergency evacuations and expensive clean up procedures. Even a small fire in a cleanroom can be disastrous to the bottom line when considering clean up costs, rebuild costs, down time/lost revenue, recertification delays, and possibly lost time injuries of key employees.

Although outside the scope of this paper, it is worth mentioning that there are roughly 6,000 laboratory worker injuries per year in the U.S., and 50,000 deaths related to unintentional exposures to hazardous chemicals.2 While there is no data available on cleanroom injury rates, there are stark similarities in many cases as to the chemical exposures present in each. Exposure to some chemicals used in cleanrooms may lead to leukemia, lymphoma, brain cancer, other serious diseases,3 and birth defects.4

This paper covers the basic classifications of cleanrooms, touches on some construction features and addresses associated hazards.

Standards of Classification

Two standards are used for cleanroom classification. The oldest is Federal Standard 209E which is used domestically. This standard uses classifications of: 1 (cleanest), 10, 100, 1000, 10000, and 100000 (dirtiest). While this standard was officially canceled in 2001, it is still widely used.5

The newest standard is TC 209 from International Standards Organization (ISO). The table below shows the equivalents of the old and new ratings systems. The graph shows particle size vs. particles per cubic foot for the different classes:

 

Infrastructure and Personnel

To get the air in a room to be particulate free, different methods can be utilized and each has their own unique advantages and disadvantages. The most common is Laminar Flow in which clean air is forced down from the ceiling, and it recirculates back through the air handling system where it is filtered again and again. Use of HEPA (High Efficiency Particulate Air) or ULPA (Ultra-low Penetration Air) filters are common.7 Forcing air at the rates needed (sometimes as much as 600 air exchanges per hour) poses property protection issues as well since heat is being dissipated from sprinkler heads.

Aside from a cleanroom being clean, many have a large quantity of infrastructure running to, from, and through them. This can be in the form of piping systems for process gases, liquids and waste materials, to increased electrical needs to feed production equipment. This usually raises the replacement cost per square foot well above any other build-out part of the facility. This coupled with the room likely being the heart beat of the operation make protection of the room paramount.

Materials and protection within clean rooms is still evolving. Cleanrooms can be hard or soft walled. Historically wet benches (plastic workstations used for various processes) needed to be protected by sprinklers or special fire-protection systems because by the time a fire propagated and a sprinkler head activated, millions of dollars of fire and smoke damage had already occurred. FM4910 addresses this wet-bench exposure by using a new plastic material that resists fire, and emits little to no smoke if it does catch fire. Duct systems over process equipment and wet benches have developed as well. They include new noncombustible materials that limit fire spread into a scrubber and prevent duct collapse during a fire event. Collapse of a duct can limit effective smoke ventilation resulting in additional smoke damage. For facilities still using combustible duct work, it is recommended that it either be retrofitted with FM4922 approved duct work or be protected with sprinklers.8

Personnel entering a cleanroom will typically enter through an airlock system, and most rooms are maintained at a positive pressure to prevent outside air from becoming a contamination concern. Special clothing is also common such as gloves, face masks, coveralls, shoe covers, etc. to prevent outside sources from contaminating the clean space. When touring a mid-grade to higher clean room (usually ISO 5 or lower), don’t be alarmed if you are asked to leave your notebook or other personal items outside of the room to help ensure cleanliness.

Codes and Standards

Typical causes of a fire include: short-circuit, spontaneous combustion of the depositions in the air ducts, or leakages of easily inflammable or self-combustible liquids and gases. Fire damage to equipment and assets can cause losses of several million dollars within minutes.9 The following codes and standards have significantly improved clean room fire prevention:

  • National Fire Protection Association (NFPA) 318 “Standard for the Protection of Semiconductor Fabrication Facilities”
  • Semiconductor Equipment Materials International (SEMI) S2 “Environmental, Health, and Safety Guideline for Semiconductor Manufacturing Equipment”
  • SEMI S14 “Safety Guidelines for Fire Risk Assessment and Mitigation for Semiconductor Manufacturing Equipment”
  • FM Global Property Loss Prevention Data Sheet 7-7 “Semiconductor Fabrication Facilities”

Each of these codes recommends the use of fire-safe construction materials for clean room applications. In cases where such materials are not used, fixed fire detection and suppression units are the recommended alternative. If neither measure is taken, the results can be catastrophic.10

Future of Clean Rooms

As technology advances, we are seeing reduced exposures within clean rooms. Traditionally, processes that once involved numerous chemicals associated with health and safety as well as environmental concerns, are being replaced with improved processes and more environmentally friendly chemicals. As these exposures decrease, so does the cost of accidents involving cleanrooms, but we have a long way to go. It also decreases concern for workers’ safety for both long and short term.

Conclusion

Cleanrooms are used by a number of industries to include semiconductor manufacturing, life sciences, biotechnology and others that have processes which are sensitive to environmental contamination. A need exists to be prudent in evaluating each process taking place in the cleanroom to ensure adequate property as well as personnel protection features are in place and maintained. Inadequate evaluation and lack of continual reassessments can lead to disaster.

Other helpful references include:

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