Desco - Questions And Answers

Is there any information related to dry (ie low humidity air) and its potential effect on static charge buildup? - Russell Morris, The Boeing Co, Seattle, WA,

Here’s some general information regarding humidity and ESD control. Please ask any additional specific questions to Service@DescoIndustries.com.

The ESD Association has a new ESD Handbook ESD TR 20.20-2000. Under Triboelectric Charge, it states:
“It is well known that static electricity, in the form of static cling and static shocks are more prevalent when the air is dry. Heating interior air in the winter months dries out the already dry air in the higher latitudes.”

Per ANSI/ESD S20.20 Fundamental Principle “All conductors in the environment, including personnel, must be bonded or electrically connected and attached to a known ground” If this is reliably done, the higher charge generation due to low humidity is not a problem.

With low humidity charges on insulators will be much higher so more important is the S20.20 section 6.2.3.1. Protected Areas Requirement
“All nonessential insulators, such as those made of plastics and paper (e.g. coffee cups, food wrappers and personal items) must be removed from the workstation. Ionization or other charge mitigating techniques shall be used at the workstation to neutralize electrostatic fields on all process essential insulators if the electrostatic field is considered a threat.”

From ESD Handbook TR 20.20 paragraph 5.3.15 Humidity “Humidity is beneficial in all ESD Control Program Plans. Contact and separation of dry materials generates greater electrostatic charges than moist materials because moisture provides conductivity that helps to dissipate charge. For this reason, ESD effects are most noticeable in the winter since heating systems reduce building environment moisture. Geographic location (desert vs. coastland) is also a major contributor to ambient conditions inside buildings. Any circumstance that results in a low relative humidity will permit a greater accumulation of electrostatic charges. Relative humidity above 30 percent in ESD protective areas is desirable as long as other adverse conditions are not created as a result of humidity levels. Generally speaking an upper limit of 70 percent is desirable to prevent corrosive effects on the metal portions of electronic devices and assemblies.”

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