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Humidity in Clean Rooms

Humidity in Clean Rooms

Clean rooms in general

A clean room is a manufacturing environment that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapors. The air inside is constantly recirculated through High Efficiency Particulate Air (HEPA) filters. Some clean rooms are entire manufacturing facilities and can cover thousands of square meters.

Clean rooms are used extensively by semiconductor manufacturers. Today, more and more biotechnology, life sciences and other fields that are sensitive to environmental contamination also use clean rooms. Clean rooms are classified according to the number and size of particles permitted per volume of air. The ISO 14644-1 is the official metric standard, which specifies the number of particles (0.1 µm or larger) permitted per cubic meter of air. The previous standard FED STD 209E was used up to 2001 and indicated the maximum of particles (0.5 µm or larger) permitted per cubic foot of air. Both standards, old and new, assume relationships between particle size and particle concentration.

Why the need to measure humidity?

Clean rooms are used in various industries: pharmaceutical, semiconductor, aerospace, food, laser and optic. Many different parameters are measured (particles, air flow, pressure…). The effects caused by humidity can be expansion, contraction, hardening and softening of materials, viscosity change of liquid, growth of microbes, and increase in static electricity, corrosion and rust. All applications have different specifications for temperature and humidity.

An abnormal level of these parameters can have a significant impact on product quality and production efficiency (perhaps even loss of production). High humidity and/or temperature can cause some instruments to go out of specification. Low humidity can generate static electricity which can then destroy the production batch as well as expensive measurement equipment. Pharmaceutical manufacturers control and record temperature and humidity according to GMP and internal quality guidelines. The semiconductor and electronics manufacturing process require vary accurate control in their clean rooms. In the food industry, it is important that the relative humidity stays under 40% thus restricting growth of bacteria and germs.

Humidity control is also important at liquid crystal display plants and paint plants. In this case, the durability and accuracy of the humidity sensor is very important. These plants generate various gases, which can affect sensor elements.