Measuring Relative Humidity in your Cleanroom

Relative humidity is a fickle issue in your cleanroom. Both outdoor and indoor factors affect it. Too much humidity will increase particulates and provide a breeding ground for biological contaminants. Too little humidity creates electrostatic discharge. Both instances can cause serious damage to your product and environment.

The ideal humidity is right around 50 percent. Humans thrive in 40-60%. Viruses, mold, bacteria, and fungi flourish above 60%. ESD is minimized right at 50%, and particle adhesion issues are unimportant at 50% and below. Controlling humidity is a mater of accurately measuring it. There are many factors that can disrupt the accuracy of your readings. Here are a couple ways to ensure your measurements are right.

Choose the best equipment.

You need the equipment to perform over an extended period of time. For this reason, performance claims on equipment are not always reliable. You need to review process and product requirements to know your required accuracy specifications. This is the first thing you need to look at when comparing equipment.

When it comes to consistency, keep in mind those things that interfere with accuracy over time. Chemical vapors in your cleanroom can keep water molecules from the sensor, creating low readings when the relative humidity is high. This same issue can cause inaccurately high readings in low humidity. If this is a concern for you, consider monitors with a heat-driven chemical purge function or other similar features.

Monitor location.

These monitors are very sensitive to multiple factors in their environments. Temperature, heat generation, and isolated moisture can all cause inaccurate readings. To avoid these issues, place your monitor in an ideal location:

  • Away from all heat sources. Heat radiating from isolated equipment will affect your reading. Even with good airflow, discrepancies can occur around equipment.
  • Segregated from itself. If the humidity sensing element and the monitor’s electronics are enclosed together, the heat from the electronics can affect the sensor’s readings.
  • Avoid places where detection is likely to be increased or decreased. Examples are near: humidification systems, cooling coils, and water sources.

Relative humidity in your cleanroom deserves careful attention. With the right preparation and equipment, you can keep humidity consistently right for the people and materials in your environment.

If you have questions about cleanroom validation or certification, contact Gerbig Engineering Company. We’ve expertly handled cleanroom equipment and services since 1985. Contact us at 888-628-0056 or email