Codes and standards regulating health care facilities can be important safety precautions at the time they are adopted, but if codes are not kept up-to-date they can become obsolete as the hospital environment changes over time. One example of this is the requirement for operating rooms to have a minimum relative humidity of 35 percent.

Humidity requirements were added to National Fire Protection Association (NFPA) codes in an effort to reduce the probability of static discharge, which was an important precaution 30 years ago when flammable anesthetics were used. Now this requirement is no longer needed, but it still remains in the 1999 edition of NFPA 99, Health Care Facilities Code, and is, therefore, required by the Centers for Medicare & Medicaid Services (CMS).

ASHE is working with CMS on this issue. We at ASHE are hopeful that a change will be made. By lowering the humidity minimum to 20 percent in operating rooms, the health care industry could save millions of dollars without compromising patient safety.

Hospital facilities would save money and energy if they only had to reach a 20 percent humidity level instead of a 35 percent level. And some hospitals in humid climates may save even more if they no longer need to install and maintain humidification equipment.

It's important to note that the money and energy saved by a lower humidity requirement would not come at a cost to patient safety. When the 35 percent humidity requirement was included in NFPA 99, there was real concern for patients because of the risk of fire and explosion when using flammable gases. NFPA 99 is focused on minimizing hazards of fire, explosion and electricity in health care facilities.

But now that flammable anesthetics are no longer used, the concern over proper humidity levels revolves around surgery outcomes. The Facility Guidelines Institute's Guidelines for Design and Construction of Health Care Facilities and American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 170, Ventilation of Health Care Facilities, have examined the issue and require a minimum humidity of 20 percent. This 20 percent minimum is justified by a scientific literature review on the potential impacts on surgery outcomes, as well as expert testimony from professionals in infection prevention and control, epidemiology, perioperative care, and mechanical and health care engineering.

Because the humidity issue has shifted away from fire concerns to clinical issues, it is now outside the scope of NFPA 99. The 2012 edition of the document recognizes this and no longer includes a requirement for a 35 percent minimum relative humidity. Instead, NFPA 99 references the 20 percent minimum from ASHRAE 170.

Until CMS changes its policy on humidity requirements or adopts the latest edition of NFPA 99, hospitals are still required to keep operating rooms at 35 percent. For more information on ASHE's efforts on this issue, along with tips on how to deal with this requirement, visit

By Chad Beebe, AIA, SASHE, director of codes and standards for ASHE.

UPDATE: CMS has lowered the operating room relative humidity requirement from a minimum of 35 percent to at least 20 percent. CMS made the change through a categorical waiver. To take advantage of the waiver, hospitals do not have to apply in advance or wait until they are cited. However, hospitals must document their decision to take advantage of the waiver and share that with survey team at the beginning of any Life Safety Code assessment.

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