Sunday, January 09, 2005

Are air temperature and humidity important to static electricity?

Are temperature and humidity important from a static electricity view?

Normal ambient temperatures are not usually an issue but from an electrostatic view but humidity is - electrostatic charge build-up problems increase at low humidities, especially < 30%rh. There is a link between temperature and humidity in that for a given air misture content, humidity approximately halves for a 10 degree rise in temperature. This is why ESD is often worst in winter (Jan-Mar) when the air is cold and dry outside and is brought in and warmed by about 15-20 degrees. Even high humidity cold air (e.g. 80%) can become low humidity (20%) when heated by 20 degrees if no moisture is added..

It is often under such dry air conditions that people feel static shocks, and in the electronics industry component damage may be exacerbated. I get many emails from people who are suffering shocks during dry air conditions, whether it be during winter (especially in northern climates) or in desert areas where the air is naturally warm and dry.


Steve Fowler said...

Moisture causes lower static in most cases simply by the extra conductivity of the water layer on surfaces which can dissipate charges generated by triboelectric actions. This works for most materials but some are so insulative and disallow moisture layer formation which could conduct electrical charges.

When vapors are being mixed with steam, however, this is a deadly mixture for high static charges. Atomized water is a high charges as was shown in the Lord Kelvin Water experiments.

The key to humidity or water giving beneficial effects for the reduction of static is that the moisture must be in a layer or stream allowing the conduction of the charges.

No isolated water droplets....

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