EMC Question of the Week: May 21, 2018
Why are electrostatic discharge events more common in dry environments?
- Moist air doesn’t experience dielectric breakdown so easily.
- Moist air has more natural ionization.
- Moist air makes material surfaces more conductive.
- Dry air makes material surfaces more conductive.
Answer
The correct answer is "c." Charge separation occurs when two non-conducting materials with different affinities for electrons make and break contact. While the two materials are in contact with one another, electrons at the boundary between the materials spend more time on the material with the higher affinity for electrons. When conductive materials are separated, electrons quickly return to their respective sides of the boundary. However when the materials are not conductive, the separation may occur before the electrons are back in place, leaving an excess number of electrons on one material and a corresponding positive charge on the other material. Repeated make-and-break contact cycles can result in significant amounts of charge accumulating on the objects in constant contact with these materials. This is fundamentally how object become charged to the thousands of volts that result in electrostatic discharge.
A slight amount of moisture on the surface of a dielectric material can raise its conductivity enough to make it "static dissipative." In other words, in a humid environment the electrons on the surfaces of the two contacting materials can move quickly enough to prevent significant charge separation from occurring when contact is broken. This is why electrostatic discharge is rarely experienced by people living in humid climates.
Have a comment or question regarding this solution? We'd like to hear from you. Email us at