IAQ, infection control in hospitals

Learn how to reduce the potential for infection and airborne pathogen dispersion in hospitals and healthcare facilities as they relate to HVAC systems and design.


Learning Objectives

1. Understand how to reduce the potential for infection and airborne pathogen dispersion.

2. Learn the codes that pertain to hospital HVAC systems.

3. Learn the importance of air cleaning and construction techniques.

The general surgery (Class B and C) operating room at Matagorda Regional Medical Center in Bay City, Texas, shows a clean environment with laminar flow air delivery served by a central station air handler containing code required filters. Courtesy: Smith Seckman Reid Inc., Thomas McConnell Photography“First, do no harm.” This is a phrase generally applied to healthcare practitioners and attributed to the meaning contained within the Hippocratic Oath. However, the same phrase can be used and applied to HVAC engineers/designers, contractors, and facility managers in the design, construction, and operation of hospitals and healthcare facilities.

Related codes and standards

As we get started down this path, there are many codes, standards, and regulations governing the design and operation of hospitals and healthcare facilities. Three prominent organizations include ASHRAE, the Facility Guidelines Institute (FGI), and NFPA. These and others draw on research and studies performed by organizations such as the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH). The goal of many of these organizations and their written standards is to improve indoor air quality (IAQ), patient and caregiver comfort, and patient and caregiver safety, and to reduce the infection rates of patients while in the hospital. Standards and guidelines produced by these organizations relate directly to the planning design and construction of healthcare facilities (FGI Guidelines-2010 and proposed 2014), Ventilation for Acceptable Indoor Air Quality (ANSI/ASHRAE Standard 62.1-2010), Ventilation of Health Care Facilities (ANSI/ASHRAE Standard 170-2008 and associated addenda), and the Standard for Health Care Facilities Code (NFPA 99-2012).

Additionally, state and local health departments, local building codes, hospital accreditation groups such as The Joint Commission, and the United States Pharmacopeial Convention have requirements and guidelines that influence HVAC design to meet the environmental and cleanliness standards that relate to patient and caregiver safety.

Deciphering these various codes can be as challenging as wading through the new hospital billing codes. As designers, we must focus on meeting codes and standards at a minimum, and we also must be aware of the bigger picture—how HVAC designs impact and influence the long-term effects of maintenance, energy use, and infection control. Again, it would seem the goal of the HVAC design is to reduce them all. When should we start thinking of how to do this? Reality and research says at the programming stage and initiation of a project; at the same time as the planning stakeholders are involved. This increases the collaboration between HVAC engineers, architects, medical planners, facility managers, and infection control and risk assessment personnel.


Good and thorough planning yields good results. Design it with good equipment, system types, and features; construct it tightly; balance it well; commission it for the long term. How many projects allow this? All of them, when we recognize what is paramount to the patient and caregiver. New project deliveries involve users, designers, contractors, and managers to produce the finished product correctly and usually at the fastest pace possible. Continuous planning through clear communication techniques, regular review meetings, acceptance and concurrence with goals and design requirements, and resolution are but a few of the requirements for a successful project.

According to the FGI Guidelines, a Patient and Caregiver Safety Risk Assessment (PaCSRA) and an Infection Control Risk Assessment (ICRA) must be done to determine what may be affected by the construction and renovation and how it must be dealt with. The health facility owner develops these assessments with input of HVAC and plumbing engineers, architects, facility managers, infection control experts, medical staff, clinical department heads, safety specialists, and other individuals with an interest in the project. Construction materials, HVAC system types and design criteria, patient flow, hand washing locations, environmental cleaning agents, and spill control/cleanup are but a few of the considerations of the assessments. If IAQ goals are required on a project, the owner should discuss them with the design and construction team to establish the ranges expected.

Figure 1: Adherence to proper occupancy separations and airflow direction can reduce the risks of infection in healthcare facilities. Courtesy: Smith Seckman Reid Inc.Renovation/addition projects are complex in that new and existing HVAC systems must get along and protect the occupants in the nonaffected areas. Adherence to proper occupancy separations and airflow direction can reduce the risks of infections (see Figure 1).

Common to each of these assessments is the HVAC design including equipment control methods, ventilation techniques, filtration, pressurization, systems reliability, air device placement, and equipment operation. All of these play an important role in patient safety, infection control, and IAQ. A design and construction phasing plan must be developed and implemented during renovation projects so the IAQ of existing occupied areas is maintained. Likewise, as a tenet to judicious HVAC system planning, once methods of IAQ and ventilation rates have been established, an operational plan should be developed to maintain the IAQ of the new or renovated space on a continuous basis. This effort should be done with the facility staff prior to project completion.

Commissioning of the facility and systems will allow for the maintenance of the systems at the required levels of ventilation and system function. Commissioning involves review of the basis of design, review of the construction documents,  functional testing, and verification that the results and operation are repeatable on a continuing basis—not just a single time when initially turned on.

Figure 2: This shows an airborne infection isolation (AII) room airflow example. Courtesy: Smith Seckman Reid Inc.Airflow direction from clean to less clean is one of the basic design features that must be used when planning and locating both HVAC equipment and space airflow. Figure 2 shows an airborne infection isolation (AII) room airflow example. The planning also includes: planning for construction including phasing; system downtime; movement of staff, patients, and public; potential reduction in patient safety; and airflow direction and pressurization.

Planning for project commissioning is a requirement of the FGI Guidelines and the project if the guidelines are adopted by the authority having jurisdiction (AHJ). Early involvement by the commissioning team aids the owner and HVAC designers in preparation of the basis of design, the functional and long-term operation and maintenance of all HVAC equipment, automatic temperature controls, and essential electrical power systems. The long-term plan is essential to maintaining the required level of IAQ and infection control in any facility. Additionally, the HVAC system planning and design must include discussions and collaboration with the architects and construction team regarding the tightness of the building or room construction to allow for the HVAC system to function correctly, maintaining the required room cleanliness, pressurization, and airflow direction that will result in the measured particle counts within the space meeting the code and/or standard criteria. For example, wall and ceiling construction that allows air leakage will negate the airflow direction from the adjacent space into the room or vice versa, creating difficult air balancing and pressure relationships that are critical to infection control protocol.

Many HVAC planning strategies have been used to improve the IAQ, some of which are more cost-effective than others.

Some strategies include:

· Pressurization control (clean to less clean)

· Purging with outside air (100% outside air with 100% exhaust air without recirculation)

· Increased ventilation rates (higher air changes per hour, ACH)

· HEPA and other filtration techniques

· Ultraviolet germicidal irradiation (UVGI)

· Room relative humidity range control (30% to 60%).

As with any strategy, a thorough risk assessment that emphasizes infection control should be performed prior to implementation.


ASHRAE 170-2008 and ASHRAE 62.1-2010 both define minimum recommended ventilation rates for occupied space; however, Standard 62.1 defers to Standard 170 for the patient occupied portions of healthcare facilities. Hospitals and healthcare facilities generally have administrative, service, and sometimes assembly-type occupancy, which fall under the Standard 62.1 criteria. Maintaining the required minimum acceptable outdoor air ventilation rates must be part of the HVAC system design and control functions. Standard 170 defines the minimum outdoor air change rate by room type as well as the minimum total ACH. Standard 62.1 defines the minimum cfm per person or cfm per square foot for various space types.

Space ventilation is accomplished by proper air movement and rates of exchange, introduction of a clean source of outdoor air, removal of contaminants (via filtration and/or direct exhaust), proper placement of the correct type air devices for the space served, and control capability to maintain the required air quantities. An assessment of outdoor air quality, including air quality and particulate measurements to determine contaminant levels, must be performed initially to determine the cleanliness and suitability for introduction into the HVAC air handling system. A wind tunnel analysis can be very beneficial to identify potential airflow or re-entrainment issues. Proper air treatment is necessary to prevent unwanted odors or contaminants from being introduced.

Figure 3: The relative size of airborne particles and pathogens. Each affects indoor air quality and must be addressed differently. Courtesy: Smith Seckman Reid Inc.Without high-quality ventilation in healthcare facilities, patients, caregivers and the public can become infected through the normal respiration of particles in the air. Poorly ventilated healthcare facilities are places where the likelihood of pathogenic particles in the air is high. Most individuals with normal, healthy immune systems can cope with and overcome the effects of these particles. However, immunocompromised patients are more susceptible to these pathogens and airborne organisms such as spores. As these organisms are found in higher concentration in healthcare facilities, additional care must be taken in the design of the HVAC systems. The provisions and requirements of each of the standards as adopted by the AHJ apply to new construction, additions, and alterations to existing buildings. See Figure 3 for a sample of pathogen type and size.

The ventilation systems serving airborne infection isolation rooms, protective environment rooms, Class B and C operating rooms, and labor and delivery rooms are required to continue to operate to maintain space ventilation and pressure relationships in the event of a loss of normal power. To enhance HVAC systems’ reliability in serving these spaces, a minimum of two units or capability to continue services upon any fan failure/component maintenance is also recommended. Additionally, space ventilation in order to provide heating is required for patient care areas unless the ASHRAE 99% heating dry bulb temperature is greater than 25 F. This requirement indicates that in most facilities, continuous ventilation will be provided at all times, unless heating for these areas is provided by other sources such as radiant panels or baseboard heating.

Research and studies cited by Farhad Memarzadeh include  S. Karra and E. Kastivela in 2007 and C.S. Cox in 1989 and 1998 and have shown that the effects of temperature and humidity (to a lesser extent) are more significant on fungi spores as they tend to be more tolerant to the stress of dehydration, rehydration, and UV radiation than viruses and bacteria. Maintaining air delivery in relative constant ranges will aid in controlling these contaminants. Studies also cited by Memarzadeh include  D.L. MacIntosh, et al., and P.C. Wu et al., and have shown that central station air handling units reduce concentrations of airborne fungi, while natural ventilation and fan coil units increase concentrations.  Studies and abstracts available through http://onlinelibrary.wiley.com, http://europemc.org, and www.ncbi.nlm.nih.gov/pubmed.

Acceptable location of air intakes and air discharges are noted in the codes to avoid potential recirculation of contaminated air and provide minimum inlet locations that will allow for a clean air location. Suspect outdoor air locations, even though meeting minimum distance requirements, should be monitored using appropriate air sensors as well as regularly scheduled portable air sampling for CO, CO2, volatile organic compounds (VOCs), NO2, and related pollutants. Don’t wait for the phone call that says someone has been taken ill due to any of these contaminants. Consider including wind tunnel testing and/or computational fluid dynamics (CFD) analysis early in the design process to minimize the potential for any adverse effects.

As with most ventilation systems, the method of air distribution, air delivery to the space, and the types of air devices greatly affect the actual air change rates and the ability of any system to minimize contaminants and/or infection. HVAC designers must follow codes and carefully choose the proper method of air delivery based on room type and function.

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