IAQ in health care settings

Engineers should use evidence-based design when engineering air systems in hospitals and health care facilities to ensure top-notch indoor air quality (IAQ).


Learning objectives

  1. Understand data from Centers for Disease Control and Prevention in order to better design hospital air systems.
  2. Know which codes and standards pertain to indoor air quality in hospitals.

Figure 1: In this post-anesthesia care unit at Oakwood Healthcare System’s Southshore Medical Building in Trenton, Mich., air quality is closely monitored. Courtesy: Peter Basso Assocs.Underlying disease, organ transplants, chemotherapy, or other factors can lead to weakened immune systems, which increase the effects of disease-causing organisms in a hospital environment. For 1 in 20 inpatients, a visit to the hospital for can cause their illness to progress and, in some cases, become terminal. Hospitals by their nature contain a higher concentration of disease-causing germs and viruses than other environments.

In the past decade, the health care industry has made tremendous strides in reducing this negative trend. However, a level of threat still exists to patients, staff, and visitors. Hospital designers, builders, operators, and employees must work together to put an end to this threat. This article attempts to shed light on the role of the HVAC engineer in preventing hospital-acquired infections (HAIs).

Hospital-acquired infections

HAIs are significant contributors to the high cost of health care. According to a 2007 report, in 2002 there were more than 1.7 million HAIs in the U.S., costing between $28.4 billion and $33.8 billion and resulting in an estimated 98,987 deaths. Recently, the U.S. government has taken measures to provide additional stimulus to reduce the incidence of HAIs. The Affordable Care Act (ACA) of 2011 provides funding for public health initiatives to further improve outcomes and reduce the incidence of HAIs by doing the following: 

  • Improve infrastructure for preventing HAIs, mainly through reporting and data analysis
  • Develop new initiatives for preventing HAIs
  • Improve the National Health care Safety Network (NHSN) and electronic reporting of lab records to reduce data entry and improve record-keeping
  • Partner with state governments to increase the number of staff dedicated to HAI prevention.

The U.S. Centers for Disease Control and Prevention (CDC) seeks to provide evidence-based guidance for infection control and prevention. On the CDC website, the 15 most common diseases and organisms involved in HAIs are listed. The site also provides guidance for patients and health care professionals on how to prevent these diseases. A brief summary is shown in Table 1. Only two of the 15 disease-causing organisms described on the CDC website are airborne.

Table 1: Common diseases and organisms in hospital environments

Based on research compiled by the CDC, this represents the most common sources leading to diseases and organism growth in health care environments, along with potential opportunities to reduce the risk of infection. Courtesy: Peter Basso Assocs., based on

More important, however, is the fact that the sources of HAI outbreaks are often not known. In a recent study in the American Journal of Infection Control, researchers studied a database of more than 1500 documented HAI outbreaks in order to shed light on the sources. Their findings revealed that in a significant portion of outbreaks the source of the infection could not be determined.


In 2008, ASHRAE, the American Society for Healthcare Engineering (ASHE), and the American National Standards Institute (ANSI) adopted a common standard for the ventilation of health care facilities. In 2010, the Facilities Guidelines Institute (FGI) adopted ANSI/ASHRAE/ASHE Standard 170: Ventilation of Health Care Facilities as part of its Guidelines for Construction of Healthcare Facilities. The FGI Guidelines are increasingly being adopted around the world as the standard to which health care facilities must be designed. Standard 170 is written in enforceable code language. The standard is a consensus document and is continuously updated with interpretations and new findings. It is scheduled to be re-issued in 2014 as part of the revised FGI Guidelines.

The main topics covered in the standard are systems, equipment, space ventilation, planning, construction, and system startup. Systems addressed are emergency power, ventilating, heating, and cooling. Equipment requirements include air handling unit design, cooling tower placement, humidifiers, and air distribution devices. Planning, construction, and startup requirements apply to the HVAC systems serving surgery and critical care spaces.

All the provisions of the standard must be followed; however, the main features that affect HVAC system design are: minimum filter efficiencies, selection and location of supply air outlets, minimum outdoor air and total air ventilation rates, air pressure relationships, and temperature/humidity requirements for various types of spaces and ease of maintenance/cleaning. While applying the standard it is critical that HVAC system designers understand the classification of the spaces they are designing for. This requires dialogue with the architects, infection control personnel, and the building’s users to understand how the spaces will be used.


Figure 2: This building information modeling (BIM) representation of Bell Memorial Hospital in Alpena, Mich., shows its associated ductwork. Courtesy: Peter Basso Assocs.Bacteria and viruses can survive on droplets or particles 5 microns or smaller and can remain airborne indefinitely; therefore, air filtration is a primary means of reducing the concentrations of airborne bacteria in hospitals. Studies have shown that 99.9% of airborne bacteria in hospitals are removed by having 90% to 95% efficient (MERV 14) filters in the air handling units. In air handling systems serving inpatient care areas, two filters are required, with the first filter upstream of fans and coils and the second filter downstream of the cooling coils and supply fan.

Standard 170 requires HEPA (MERV 17) filters for protective environment rooms designed for patients with high susceptibility to infections. The standard does not address the use of ultraviolet radiation lights inside of air handling units as a means for killing pathogens; however, some studies have shown that these devices can be effective in preventing microbial growth.

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