Health Care Standard Update

ANSI/ASHRAE/ASHE Standard 170-2008, Ventilation of Health Care Facilities, can be adopted by authorities for health care facility construction and private national organizations such as the Facilities Guidelines Institute (FGI). In 2010, FGI incorporated Standard 170- 2008 as Part Six of its Guidelines for Design and Construction of Health Care Facilities.1 This includes all addenda, present and future, issued by ASHRAE. The Joint Commission, federal agencies and authorities in 42 states use the Guidelines either as a code or a reference standard when reviewing, approving, and financing projects or when surveying, licensing, certifying or accrediting newly constructed facilities, according to FGI.

In addition, ASHRAE Standard 62.1-2010 recently eliminated normative Appendix E “Ventilation Rates for Health Care Facilities.” These changes to the FGI Guidelines and Standard 62.1 have resulted in one national standard for health care ventilation requirements.

The project committee identified and reconciled differences between the 2006 Guidelines2 and Standard 170-2008, which are reflected in the incorporation of the standard into the 2010 Guidelines. Several addenda to the standard have been published, which provide updated requirements to: address committee input and suggestions, improve coordination between the standard and the FGI Guidelines and reflect determinations from proposed changes and requests for interpretations.

Standard 170 Addenda

Addendum a (published) clarifies four items related to Table 7-1: “Design Parameters,” including the temperature for newborn intensive care, is changed to 72°F – 78°F; and Note k is changed to read “The RH ranges listed are the minimum and maximum allowable at any point within the design temperature range required for that space.”

Addendum b (published) addresses 10 issues:

  • HEPA filters are specified in Table 6-1, “Minimum Filter Efficiencies” for protective environment rooms. (This eliminated a reference to a MERV 17 designation.)
  • Relief air discharge is an allowable exemption from the 25 ft (8 m) separation requirement.
  • Design parameters for intermediate care rooms are now included in Table 7-1.
  • Pressure relationships for critical and intensive care and wound intensive care are now N/R (no requirement). The rationale for the change in Standard 170 is twofold.

1.The FGI Guidelines and prior editions of the Guidelines, had no requirement for airflow in or out of these types of rooms; and

2. A literature review of infectious disease literature was conducted for burn/wound care units, revealing no evidence-based studies demonstrating increased benefit from negative or positive pressure. This was not unexpected since health care-associated infections in such patients involve direct/indirect contact and infectious agents are primarily waterborne/moisture related microbes—not airborne.

  • Operating rooms are required to have individual temperature control.
  • The HVAC provisions for morgue and autopsy rooms have been clarified including a minimum differential pressure requirement of –0.01 in w.c. (–2.49 Pa).
  • The endoscopy room is clarified to be a gastrointestinal endoscopy procedure room, and the minimum total air change rate is reduced to 6.
  • A requirement for MERV 7 filters in recirculating room HVAC units is added. This was subsequently revised in Addendum h.
  • Filter blank-off panels and seals are now required to minimize unfiltered air from bypassing filters.
  • The title of the humidity column in Table 7-1, “Design Parameters” is changed to “Design Relative Humidity.” It was discovered that certain regulatory agencies were interpreting the humidity ranges in this column as absolute; meaning no excursions above or below these ranges was acceptable. Just as expected with temperature, the actual relative humidity experienced in a space may be outside these ranges when outside conditions exceed design conditions.

Addendum d (published) was published in July 2010. This addendum revised the design relative humidity range for eight short-stay rooms to 20% to 60%. These rooms are indicated in Table 1.

The basis for the lower humidity included a review of scientific literature on potential impacts of lowering RH from 30% to 20% on outcomes of surgery and other procedures commonly performed in the listed spaces. Data presented resolved issues related to static electricity or RH effects on equipment. Since flammable anesthesia is no longer an issue for operating rooms, the remaining question revolved around the perception that lower RH conditions affect infectious outcomes.

Addendum d is the result of a solicited proposed change to the standard that addressed the impact of RH on viral infections; this was examined first. Several studies were considered relevant to the assessment of the risks of viral agents and supporting the decision to allow a greater range of humidity.3, 4, 5 No studies were identified documenting the effect of RH on viral agent survival below 20%.

The investigation next moved to the examination of infectious disease outcomes, i.e., surgical site infections (SSI) in settings such as ORs. It was determined from the literature that SSIs are not caused by environmental viruses—only bacteria or fungi. The few studies specifically associating SSI with temperature and RH involve prolonged periods of RH exceeding 60%.6 Reviews conducted by Memarzadeh8 further noted that survival and growth of bacterial agents are less likely at lower temperatures and RH. Members of the committee concluded that the issue of lower RH in these settings for patients and staff is related to comfort and not infection, further supporting adoption of Addendum d.

Addendum e (published March 2011) clarifies ventilation provisions for airborne infection isolation (AII) rooms and paragraph 6.3.2 “Exhaust Discharges.” The addendum reinforces that the exhaust ductwork from rooms such as AII rooms, bronchoscopy rooms, emergency department waiting rooms, etc., should be maintained at a negative pressure as it passes from these rooms to the exhaust fan. If the exhaust fan is located in a mechanical room, vs. on a roof, the interior ductwork that is on the discharge of the exhaust fan needs to be sealed to SMACNA Seal Class A.

Addendum f (published March 2011) provides some clarifications related to the pressure requirements for AII rooms, and protective environment (PE) rooms. The stipulation that the differential air pressure measured between the AII room and the corridor is a small, but important clarifying statement.

Addendum f also addresses a new category, the “Combination Airborne Infection Isolation/Protective Environment Room.” This room and its associated anteroom were added to the 2010 Guidelines to address the case of an immunosuppressed patient who also has an airborne infectious disease. The pressure relationships of the required ante room, combination room and adjacent areas is a key aspect for the proper design for this room, and is detailed in the addendum. The ventilation requirements of 2 outdoor air/12 total ach are similar to that for the AII and PE rooms. (Table 2 is an excerpt from Addendum f.)

To reduce energy use in hospitals, the minimum total air change rate for AII may be reduced to 6 ach when the room is not being used for an infectious patient. The pressure relationship to adjacent spaces must remain negative in this scenario.

This addendum reaffirms that switching controls to change the pressure relationship of a room from negative to positive or from positive to negative are prohibited. Implicit within the addendum is a clarification that the “no requirement” should not be interpreted to mean “neutral” pressure.

Addendum g (to be published spring 2011) allows, with certain caveats, the use of type D diffusers for single patient rooms. Within Standard 170, Table 6-2, “Supply Air Outlets,” prescribes supply air diffusers in accordance with the classification systems of the 2005 ASHRAE Handbook—Fundamentals, Chapter 33, “Space Air Diffusion.” The standard, previously, did not permit displacement ventilation because the necessary diffusers were not listed in Table 6-2. This addendum reflects the committee’s deliberations throughout 2009–10, regarding the applicability and potential benefits of displacement ventilation systems for patient rooms. Addendum g is based upon recent research.7

Selected proposed addendums are summarized in Table 3. (Note: These are proposed addenda that are subject to public comment and subsequent changes and adjustments.)

Proposed Addenda and Changes

Recirculating room HVAC units. The two major focuses of proposed Addendum h are filtration and ventilation requirements for spaces served by recirculating room HVAC units. These systems may be based on heat pumps, fan-coil units, induction units, or other similar recirculating equipment. Addendum h stipulates that “All of the air provided to a space shall be filtered in accordance with Table 6-1 except as otherwise indicated in Section 7.1 for spaces which allow recirculating HVAC room units.” And, it stipulates that recirculating room HVAC units “shall not directly condition the minimum outside air changes per hour flow to that space.” The intent of these requirements is to encourage the use of a central air-handling system for conditioning of outside air, whenever recirculating room HVAC units are used, and to ensure that all air (primary or recirculated) is filtered appropriately.

Residential health care facility filtration. The primary focus of Addendum j is to update filtration requirements for several residential health care occupancies, which were previously included in the 2006 Guidelines. For central air-handling systems, a second filter bank (MERV 13) is required for certain resident areas in nursing facilities (including skilled nursing), and a first filter bank (MERV 7) is required for hospice and assisted living facilities. This update maintains the two bank requirements of the 2006 Guidelines for nursing facilities, and eliminates the 2006 Guidelines requirement for the second filter bank in hospice and assisted living facilities.

Chilled beams. The committee has spent considerable time over the past year deliberating on the application of chilled beams in health care settings. The committee continues to discuss condensation prevention, maintenance, and field testing of chilled beam systems.

Multiple spaces provisions (multiple zone systems). A proposal was considered by the committee to apply the procedure described in ASHRAE Standard 62.1 for multiple-zone systems for determining the amount of outside air to be sup¬plied in health care occupancies. After careful deliberation, the committee rejected this proposal due to the basic differences in why the outside air is needed. For the purposes of Standard 62.1, outside air is needed for general dilution of indoor contaminants. Standard 170, on the other hand, is significantly concerned also with infection control. The committee is continuing to analyze the potential for the applicability of the procedure for multiple-zone systems in health care occupancies.

Future Issues

In addition to the items mentioned here, the committee has other issues to consider such as energy recovery, ducted return air systems, reserve capacity for domestic hot water, location and quantity of operating room return air grilles, emergency department requirements, differential pressure for bronchoscopy rooms, and acoustic and vibration control issues. In addition to these items, the committee intends to spend additional time reviewing outpatient and residential health care facility requirements. The results of these efforts will be seen in future addenda.


Standard 170 has benefited from the ASHRAE process of continuous maintenance. The published addenda and proposed addenda are the result of committee member initiatives, proposed changes, and requests for interpretations. This process also permits the FGI Guidelines to be updated between the four-year revision cycles. This standard is continuing to improve due to active interest by the membership of ASHRAE, FGI Health Guidelines Revision Committee (HGRC) members, the membership of the American Society for Healthcare Engineering (ASHE), and the public at large.

Author Note

At the ASHRAE Winter Conference in Las Vegas, January 2011, use of the multiple zone system calculations of Standard 62.1 was reconsidered; and its applicability was supported by the committee and a future addendum will be issued for public review and comment.


    1. Facilities Guidelines Institute. 2010. Guidelines for Design and Construction of Health Care Facilities. American Society of Healthcare Engineering.
    2. AIA. 2006. Guidelines for Design and Construction of Health Care Facilities. American Institute of Architects.
    3. Tang, et al. 2006. “Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises.” Journal of Hospital Infection 64:100 – 114.
    4. Lowen, et al. 2007. “Influenza virus transmission is dependent on relative humidity and temperature.” PLOS Pathogens 3(10).
    5. Shaman, K. “Absolute humidity modulates influenza survival, transmission, and seasonality.” Proceedings of the National Academy of Sciences.
    6. Centers for Disease Control and Prevention (CDC) and Healthcare Infection Control Practices Advisory Committee (HICPAC). 2003. “Guideline for environmental infection control for health care facilities.”
    7. Healthcare Ventilation Research Collaborative. 2009. “Displacement Ventilation Research – Phase II Summary Report.”
    8. Bartley, J., L.K. Archibald, F. Memarzadeh, R. Conner. 2010. ASHE/FGI Workshop. “The Role of Humidity in Operating Rooms—Demystifying the Myth.” .



      1. Bartley J.M., R.N.O. Olmsted, J. Haas. 2010. “Current views of health care design and construction: Practical implications for safer, cleaner environments.” Am J Infect Control 38:S1–12.
      2. Ninomura, P., R. Hermans. 2008. “Ventilation standard for health care facilities.” ASHRAE Journal (50)10.
      3. Ninomura, P., et al. 2006. “Updated guidelines for design and construction of hospital and health care facilities.” ASHRAE Journal (48)6:H33.

“Health Care Standard Update” was published in the March 2011 edition of the ASHRAE Journal.
Authors: Christopher P. Rousseau, PE – Newcomb & Boyd; Paul Ninomura, PE; Judene Bartley

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