The Devilish Details of Humidity Measurement in GxP-regulated applications

Janice Bennett-Livingston
Feb 14, 2013
Life Science

This week’s blog is about something that Vaisala does very, very well: Humidity measurement. Not to toot our own horn, but it’s a hard measurement to make, as anyone who has ever tried to measure it over an extended period of time knows. Moisture content in the air is tough to accurately quantify, but, quantify it we must, because there are few processes and substances that are not impacted by humidity.

In almost every process involved in creating and distributing drugs, biologics, and medical devices humidity is a central factor in ensuring repeatable, efficacious results. Humidity-critical processes range from tableting or powder processing wherein nearly all properties of a substance will be affected by moisture, to clean room environments with pre-defined upper and lower limits of humidity.

One of our in-house experts on humidity measurement in regulated environments is Jim Tennermann, Segment Manager for Vaisala Life Science. According to Jim, the most common sources of error in humidity measurement include:

  • Poor sensor location
  • Local convective heat problems
  • Sensor contamination (airborne or condensation)
  • Seasonal changes

Jim recommends that after ruling out the error sources outlined above, sensor stability becomes the most important factor in accurate humidity measurement. Understanding accuracy over time will allow facility and quality managers to anticipate and plan against common humidity headaches. “Accuracy specifications shouldn’t necessarily be the ultimate decision point,” says Jim. “Especially when there are risks of inaccurate measurement inherent to the application. Long term stability is a far more significant factor in evaluating a humidity instrument’s performance.” Read Jim's blog on water vapor in tablet coating applications on

To learn more about humidity sensors in clean rooms and other controlled environments, you can read Jim’s article: “The Devil is in the Details” below. Also of interest, “The many Faces of Water Vapor: Relative Humidity, Dewpoint, Mixing Ratio” describes in detail the different properties of gas mixtures and moisture in the air.



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