New Guidance on Humidity Levels in the Operating Room


This Issue

A change in the standards regulating a hospital’s physical environment in the operating room (OR) may conflict with the instructions for use on some equipment and supplies routinely used in surgery. To ensure patient safety during surgery, the AHA in collaboration with its personal membership groups, the American Society for Healthcare Engineering (ASHE) and the Association for Healthcare Resource & Materials Management (AHRMM), urge hospitals to examine their humidity levels in the OR and consider the effects on equipment and products used during surgery. This advisory and associated attachments will assist in your assessment.


Many safety codes and standards regulating the healthcare physical environment now require relative humidity levels in operating rooms (not other areas of the facility) to be at least 20 percent, a change from the 30 percent minimum humidity required by some previous editions of codes. The 20 percent threshold provides hospitals with flexibility during construction and saves operational costs by requiring less humidification. Although the change to a 20 percent minimum level is a positive development, it may pose challenges for hospitals using equipment and supplies originally designed to be used in an operating room environment with at least 30 percent relative humidity.

The AHA, ASHE, and AHRMM have been exploring this issue with other organizations, including the Association for the Advancement of Medical Instrumentation (AAMI). New guidance from this group of stakeholders outlines some of the issues raised by moving to a minimum 20 percent humidity level in operating rooms. The joint guidance explains that:

  • Relative humidity can affect the shelf life and product integrity of some sterile supplies. Some products, such as EKG electrodes used for patient monitoring, are especially sensitive to humidity.
  • Some electro-medical equipment, particularly older model equipment, may be affected by electrostatic discharge commonly occurring at low humidity levels.
  • Supplies and equipment have manufacturer’s instructions for use (IFUs) that explain any required environmental parameters, which may or may not include relative humidity requirements.
  • IFUs from the manufacturer should be followed.
  • Health care facilities should consider the effects on equipment and/or supplies before reducing operating room relative humidity below 30 percent.
  • Many supplies can be used outside of the minimum humidity requirements but should not be stored for long periods in low humidity conditions.

Next Steps

  • Share this advisory with your chief operating, information, nursing and medical officers, head of surgery, facilities manager, engineer, materials manager, risk manager and other relevant staff.
  • Ask that they review the attached guidance and consider its implications for your operating rooms.
  • The guidance outlines eight questions for health care facilities to consider before using relative humidity levels below 30 percent in operating rooms. In addition, ASHE has created a on the following page to help facilities determine whether a lower relative humidity is appropriate. Use these tools to consider whether additional action is needed in your facility to ensure continued safety in your operating rooms.

Further Questions

If you have additional questions, please contact AHRMM’s Michael Schiller, CMRP, director of supply chain at; ASHE’s Jonathan Flannery, CHFM, FASHE, senior associate director of advocacy, at; or AHA’s Evelyn Knolle, senior associate director of policy at

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