Humidity requirements for an ESD control program FAQs

EOS/ESD Association, Inc. is frequently asked about humidity requirements for an ESD control program. This document provides more information and answers some of the frequently asked questions regarding humidity in an ESD control program.

Q: Is humidity a requirement in ANSI/ESD S20.20?

A: Humidity control in relation to an ESD control program continues to be misunderstood across the industry. Historically, humidity was considered to be a good method of ESD control as it was shown to reduce perceived shocks by personnel working in the environment. As ESD control program standards have matured over the years, the need for humidity control has been eliminated as product qualification methods have become more robust.

If a company meets the requirements of ANSI/ESD S20.20 or IEC 61340-5-1, the ESD control items used to mitigate risks of ESD shall be qualified prior to their initial use within the ESD control program. Most of the ESD control items require environmental conditioning during the product qualification testing process, this is typically conducted at 12% ± 3% RH and 23 ℃ ± 3 ℃. If the ESD control item being qualified meets the requirements of ANSI/ESD S20.20 or IEC 61340-5-1 then humidity controls are not required as the item has been shown to function in a worst-case environment.

In the most recent revisions of ANSI/ESD S20.20 (-2021) and IEC 61340-5-1 (edition 3, to be published soon), organizations are allowed to complete product qualification at the lowest annual humidity the facility experiences. This lowest annual humidity may be due to ambient conditions where the facility is located or may be due to other factors such as environmental conditioning of the facility. For example, if the lowest humidity level in the facility is 30% RH, then any ESD control items that are used within the facility may be qualified at or below 30% RH. ESD control items that leave the facility, for example packaging, must still be qualified per the standard test method as the environment the ESD control item may be exposed to is unknown.

Q: My organization recently installed a flooring system and we plan to qualify our footwear/flooring system. It is currently summer, and the relative humidity is 50%, in the winter we expect the relative humidity to drop to 20%, what should we do?

A: Product qualification must be completed per the requirements of ANSI/ESD S20.20, this allows for two approaches, either you qualify per the standard test method, or you qualify at the facility’s lowest annual humidity. If you plan to qualify per the facility’s lowest annual humidity an acceptable approach would be the creation of a testing plan, where you complete product qualification measurements over a period of time until you capture data at the lowest annual humidity.

Q: My organization’s facility controls humidity to 30% RH but our records show a small time period where it dropped to 28% RH, is this considered a non-conformance?

A: It depends. The amount of change in relative humidity and the length of time are crucial factors in determining risk. In general, a low risk would be determined by a small change in humidity and a short time period.

Product qualification test methods typically have a ±3% RH tolerance to the environmental conditioning requirements, this tolerance could be applied to the facility’s minimum humidity limit. In the example above, if humidity dropped to 27% RH it may be an acceptable risk, however, anything lower than 27% RH may be considered a non-conformance.

When humidity changes it can take time for the materials in the environment to acclimatize to the new environment. In the example above, if the humidity dropped below the organization’s limit by 3% RH or more for only a few minutes this would be low risk. However, if this occurred for multiple hours this may be considered a non-conformance.

In either situation, the organization should gather additional objective evidence to determine whether it is deemed safe to handle ESDS items including increased compliance verification of ESD control items or process assessment during this period. If it is determined that the program limits are being exceeded, handling of ESDS items shall be stopped. If the objective evidence indicates handling of ESDS items is acceptable (for example, ESD control items meet program requirements), this information shall be captured and stored as a record.

Q: What if our program specifies humidity conditions as an ESD control.

A: If your company’s ESD control program plan specifically mentions humidity control levels, it must be monitored and there must be objective evidence to indicate that. There also needs to be a procedure on how the process reacts when humidity is outside the specified range. If humidity is not specified in your ESD control program plan, monitoring humidity levels is optional but a good practice.

Q: What do I do if the humidity levels in my facility are lower than the environmental conditions of 12% ± 3% relative humidity called out in the EOS/ESD Association, Inc. standard test methods for ESD control item qualification?

A: All ESD control materials and items used in your facility must work at the lowest humidity level experienced at the facility or at least 9% to 15% relative humidity. If your facility experiences humidity levels lower than 9%, it is recommended to verify that the ESD control items still function properly at the lowest level experienced at the facility. Materials such as flooring, worksurfaces, garments, wrist straps, packaging, etc. that meet EOS/ESD Association, Inc. and IEC standard test methods should work at even lower humidity levels, but it is best to verify. This can be done with random resistance to ground testing on workstation items during extremely dry days.

Q: So why doesn’t the EOS/ESD Association, Inc. require humidity control as part of the ESD control program?

A: ASHRAE had commissioned studies on humidity and electrostatic control. While it shows humidity does help in the reduction of charge accumulation, it also shows that it does not control charge accumulation to reduce risk to sensitive items. The differences in electrostatic charge accumulation on insulators from 20% to 30% RH at room temperature are minor. But the primary reason that humidity is not part of the control program is the fact that ANSI/ESD S20.20 (as well as IEC 61340-5-1) requires that the qualification of all ESD control items be at 12% ± 3% relative humidity at 23 °C ± 3 °C.

As a result, the EOS/ESD Association, Inc. is not relying on humidity as part of a control program in ANSI/ESD S20.20.

Please send an email to if you have additional questions regarding humidity controls in your ESD control program.