Portable Gas Flow Meters for Cleanroom Metrology

Portable gas flow meters are a simple solution to two key challenges associated with cleanroom metrology. The first is the strict cleaning and sterilization requirements to ensure no contaminants are introduced into the environment, and the second is a lack of electrical outlets to minimize crevices where bacteria can grow.

Metrology is critical for cleanroom equipment such as HEPA filters, and for instruments working in the cleanroom such as mass flow controllers used to feed bioreactors. Ensuring that both the cleanroom itself and all of the equipment inside the cleanroom are calibrated and in spec ensures that all pharmaceutical products are safe for use (cGMP cleanrooms) or that all electronics will work correctly (semiconductor cleanrooms).

To meet industry requirements, cleanrooms must be consistently monitored. However, bringing electronic equipment for testing and verification into cleanrooms can be complicated. In this article, we discuss the monitoring requirements for cleanrooms and the challenges in introducing metrology equipment into them. Finally, we discuss portable gas flow meters as a simple solution to the challenges of metrology in and for cleanrooms.

Cleanroom design is based on a large number of factors which together minimize the contaminants that are able to enter the area.

• HEPA filtration ensures that contaminants which do enter are diluted to appropriate levels (an amount specific to the application and cleanroom type).
• Temperature and humidity control creates conditions that are optimal for the process (or for the operators, if the process is sealed from the ambient cleanroom conditions).
• Walls and floors must be seamless, constructed of non-shedding materials which can be wiped down and easily cleaned and maintained.
• Ceilings must support filters and lights which are sealed and airtight, with their produced heat taken into account in all cleanroom calculations.

All of these factors are carefully engineered — but humans entering and leaving the cleanroom introduce the biggest risk for contaminating the cleanroom. Gowning areas and procedures are therefore also prescribed and monitored. While the specifics vary by application and facility SOP, cleanrooms are generally monitored daily, with additional testing performed annually by independent agencies.

Key elements of cleanroom design include eliminating as many bumps and crevices as possible in both the room itself and in any equipment, and ensuring all surfaces are compatible with cleaning agents and disinfectants. This is done to avoid contamination, as microbes, dust, and other contaminants most successfully evade cleaning procedures when in these crevices. Therefore, equipment must have extremely smooth surfaces (electropolishing is often required), and lights and power points must be well integrated into the room. Any outlets present are generally fully recessed, which prevents sharp edges and the risk of exposed cabling. Since cleanrooms are generally designed by first determining where the equipment will go and then coordinating power points around that plan, there are generally very few power sources left unused. In short — outlets inherently have crevices, and are therefore few and far between in cleanrooms, designed to be available only where truly necessary. This creates a challenge for monitoring, calibration, and other metrology work which does not occur on a daily basis and is therefore not designed into the cleanroom layout. The instruments required to perform this monitoring are most often electronic, and need to be plugged in to ensure that the cleanroom and the process equipment are operating healthily and per SOP.

Portable, rechargeable meters provide a neat solution to the problem of too few outlets for metrology in cleanrooms. They can be housed and charged outside of the cleanroom, then brought inside as necessary. Once within the cleanroom, they do not require any power points or outlets to operate. For example, mass flow meters can be used to check and calibrate the mass flow controllers or rotameters feeding gases into bioreactors. To calibrate the controllers inside the cleanroom, the portable meter simply needs to be wiped off with lint-free wipes in the gowning area and then brought inside. Transferring equipment and materials into cleanrooms is always challenging. Local SOP will dictate the specifics, but the process of introducing new things into cleanrooms requires paying careful attention to wiping down packaging, changing gloves, and fully following detailed procedures. However, these procedures are well established, and pose less risk of contamination than an unused outlet in the cleanroom. As such, portable gas flow meters are a powerful tool for the metrology performed in cleanrooms.