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Tip of the month: Keep tabs on proposed humidity range reductions


March 1, 2010

Tip of the month

Keep tabs on proposed humidity range reductions

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has proposed a modification to its Standard 170-2008, Ventilation of Healthcare Facilities, reducing the lower end of the recommended relative humidity (RH) range for short-term patient treatment stays—even in operating rooms (OR)—from 30% to 20% RH.

Short-term spaces covered in the standard include:

  • Class A, B, and C ORs
  • Operating and surgical cystoscopic rooms
  • Delivery rooms
  • Treatment rooms
  • Trauma rooms
  • Laser eye rooms
  • Gastrointestinal endoscopy rooms

The top of the range remains 60% RH.

A more realistic approach, say supporters

The idea behind the change, according to ASHRAE, is to bring the standard up to date with current practices and thinking in the healthcare industry. Decades ago, hospitals determined that at least 30% RH—which can be difficult to maintain in many buildings—served as an infection control measure.

After reviewing research with the help of the Centers for Disease Control and Prevent and the Association for Professionals in Infection Control and Epidemiology, ASHRAE determined that maintaining 30% RH does not reduce infections.

Further, a claim appears in NFPA 99, Healthcare Facilities, stating that 35% RH should be maintained in ORs for fire safety reasons.

In an alert discussing the ASHRAE humidity standard modification, the American Society for Healthcare Engineering theorizes that the 35% threshold came about back when OR practices included flammable anesthetics not used today.

As such, the NFPA eliminated the 35% RH standard for ORs in drafts for the 2012 edition of NFPA 99.

At presstime, the public comment period for the standard modification had just closed.

If the change is approved, it will become an official modification to the 2010 edition of the Facility Guideline Institute’s Guidelines for the Design and Construction of Health Care Facilities.

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