October 13, 2010 | | Comments 4
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Mac’s Safety Space: Humidity in the operating room

Q. I have a question regarding OR humidity. If OR humidity drops below the required range, can a portable reservoir type humidifier be used to bring the humidity back up within range? If not, what should the facility do? Should the facility stop surgeries?

I have been researching the World Wide Web to find additional information. What I have found is that reservoir type humidifiers should not be placed in duct work. Any additional help would be greatly appreciated.


A. The humidity levels are very much in the way of guidelines as opposed to strict regulations. Recently, ASHRAE (the American Society of Heating, Refrigeration and Air-Conditioning Engineers) dropped the lower control limit for humidity to 20%, basically because electrical systems and OR environments in general are much better designed and can safely tolerate a “drier” environment.

At the end of the day, it all comes down to the comfort of occupants, and as long as the OR rooms aren’t dripping condensation, the infection control risks are minimal. However, if you are dealing with humidity levels below 20%, I would contact your HVAC vendor and see what type of humidification is available.

You are correct in that reservoir-type humidifiers should not be placed in duct work, but there is humidification equipment that can be installed for those really dry days.

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Steve MacArthur About the Author: Steve MacArthur is a safety consultant with The Greeley Company in Danvers, Mass. He brings more than 30 years of healthcare management and consulting experience to his work with hospitals, physician offices, and ambulatory care facilities across the country. He is the author of HCPro's Hospital Safety Director's Handbook and is contributing editor for Briefings on Hospital Safety. Contact Steve at stevemacsafetyspace@gmail.com.

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  1. AORN guidelines recommend against using humidifiers due to bacteria aerosolization.
    low humidity creates an increase risk for fire due to electrostatic charges used in an oxygen rich environment and around flammable substances – preps and drapes.
    We do a huddle with sr. leadership, division chiefs/surgery/anesthesia to determine a plan. In the past we have opted to stop elective cases until the temp/humidity can be in range, only allowing urgent/semi-urgent to proceed.

  2. Low humidity levels can produce a static electric discharge between staff passing instrument or possible to the patient. 20 years ago, this was a concern when levels dropped near or below 10% in northern dry cold climates in the upper Midwest, typically when winter temperatures dropped below zero. The humidification system did require additional humidification measures to maintain the 30% guidance at that time. During the winter season, additional steam injectors in the HVAC system raise the humidity to appropriate levels. I also suggest you contact an HVAC contractor for resolution.

  3. We recently were cited for humidity readings that dropped just below 35% but never below 30% by CMS. What is the requirement and what regulation applies?

  4. Steve MacArthur

    Hi Tim,

    What you experienced was one of those fabulous instances in which there was a confluence of misfortunes – an edition of an NFPA code (NFPA 99 2005 edition) and an industry standard (the American Society of Heating, Refrigeration,and Airconditioning Engineers – ASHRAE) don’t see eye to eye and we end up being blindsided (mixing a couple of metaphors there). Recently, ASHRAE updated their standard for ventilation in healthcare Standard 170-2008, Ventilation of Healthcare Facilities, it dropped the minimum humidity level to 20%, based on technological improvements, infection prevention concerns etc. But Steve – I got cited for being less than 35% (which could include 20%), so what’s up with that?

    Unfortunately, the ASHRAE standard, which would nominally be characterized as a concensus standard, and thus sort of not binding, being a little ahead of its time, gives a little more flexibility than the 2005 edition of NFPA 99, which requires:

    6.4.1.1* The mechanical ventilation system supplying anesthetizing locations shall have the capability of controlling the relative humidity at a level of 35 percent or greater.

    Now, the devil’s advocate in me would say that while the above statement provides guidance for those who would be inclined to seek guidance, it doesn’t really get in to the “thou shalt” category. I have a sneaking suspicion that your HVAC equipment has the capability of controlling the relative humidity at a level of 35 percent or greater, which, strictly speaking, equates with compliance with the requirements of NFPA 99.

    So, it kind of leaves you in something of a corner; I don’t know that you might be able to have a discussion with the CMS surveyor (in many cases, once the initial survey is complete, they encourage you to work with them to achieve compliance) and work through this (particularly as, in the absence of a time machine, you can’t really go back and change the humidity levels). Maybe armed with the ASHRAE standard (available on their website http://www.ASHRAE.org), you can negotiate a favorable settlement.

    You’ve already been cited, so I shouldn’t think that you’d be incurring any additional risk by asking to talk.

    Best of luck

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