Relative Humidity - Requirements

What are relative humidity requirements for critical spaces?

The Joint Commission expects organizations to have a process in place to demonstrate that proper humidity (RH) levels are maintained. NFPA 99-2012 includes ASHRAE Standard 170-2008, Ventilation for Health Care Facilities, and it applies to new facilities only. Existing spaces should be maintained as originally designed with parameters identified by the organization. In April 2013, CMS issued a categorical waiver in its Survey and Certification (S&C) letter 13-25-LSC & ASC that allowed the lower limit to 20% RH for anesthetizing locations based on ASHRAE 170-2008, Addendum D. Note that Addendum D does not apply to sterile storage locations that are not in the OR where a maximum of 60% RH is recommended in ASHRAE 170-2008. The organization should develop its process using evidence-based guidance, including the manufacturers' instructions for use (IFUs) to ensure that the supplies in these locations are not impacted at lower levels.

Please be aware that CMS also issued S&C letter 15-27 that advises organization to follow manufacturers' recommendations for equipment and sterile supplies in the operating room (OR) environment to ensure that the humidity levels in the ORs are compatible with the manufacturers' IFUs for the supplies and equipment in that setting. Where the requirements of the equipment or supplies conflict with the space conditions, the organization should take action to prevent an adverse condition. [EC.02.05.01]
Last updated on August 29, 2017
Manual: Hospital and Hospital Clinics
Chapter: Environment of Care EC

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