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.

By J. Patrick Banse, PE, LEED AP, Smith Seckman Reid, Houston February 7, 2013

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.

“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.

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.

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.

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 https://onlinelibrary.wiley.com, https://europemc.org, and https://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.

Air treatment, filtration, cleaning

All air delivery systems require filters to remove particles from the airstream to keep equipment clean and functional as well as reduce dust and contaminant distribution through the air systems. ASHRAE Standard 170-2008 identifies the minimum number and location of filter banks required with filter minimum efficiency reporting value (MERV) ratings based on space designation by function. Two filter banks are required for patient care areas. See Table 1 for filter MERV ratings and particle removal efficiency. The higher the potential for infection or the more immunodeficient a patient is (and therefore the cleaner the air required), the higher the required filter rating. Studies cited by Memarzadeh contained in the Aerobiological Engineering Handbook on Airborne Disease and Control Technologies (McGraw Hill) by W.J. Kowalski in 2005 showed multiple options for increasing the ability of specified filters to prevent spores from entering a building, including biocidal filters, electrostatic filters, carbon adsorbers, low-level ozonation, and negative air ionization.

In addition to filtration, pressurization control is used to prevent migration of fungi spores and bacteria from one area to another. Systems that use 100% outside air without any recirculation have been used successfully to minimize contaminants. HEPA filtration has also been used to improve IAQ by trapping fungi spores and most bacteria. Care must be taken in the placement of filters in equipment and air systems to keep filters dry, as a wet filter may cause spores to grow through the filter media, creating more problems than the filter was supposed to solve. The proper code-specified minimum distances and good engineering practice for filter installation from cooling coils and humidifiers must be maintained to prevent moisture collection.

As with any HVAC strategy, the design and implementation must be in line with any owner/user established project microbial and particulate IAQ goals. To achieve the goals using particulate filters, first the particle size must be known and then the minimum filter MERV rating chosen to trap and remove the particles from the airstream. ASHRAE Standard 52.2-2007: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size identifies the minimum MERV rating for preventing infiltration of fungi spores at 9 to 12, and bacteria at 13 to 16. Studies also indicate that the use of HEPA filters is most effective in positive pressure rooms such as operating rooms and protective isolation rooms. Additionally, research shows that for HEPA filters to be truly effective, they must be used with higher air change rates and controlled air velocities across the filter to maintain effectiveness, along with tightly sealed rooms. This is one of the reasons that Standard 170 does not require HEPA filters in other locations. Viruses are much smaller than bacteria and require specialized air treatment, and thus are beyond the scope of this article.

All filters must be tight-fitting within their holding frames to properly function. Air bypass around any filter increases the likelihood of airborne pathogens to be distributed into the occupied space. Type 8 holding frames for both prefilter and final filters with proper fastening clamps and devices will minimize any bypass and increase the filter effectiveness. Odors and VOCs have been successfully removed using carbon adsorbers or higher outside air dilution rates.

The use of UVGI in combination with lower MERV rating filters has shown to be an effective alternative to HEPA filters in less critical applications. UVGI has also proven effective to control microbial growth on cooling coils, and continuous UV exposure will inhibit fungal growth in airstreams; however, the effectiveness is dependent on the contact time and distance to the UV source. Multiple air passes will increase the exposure and the potential benefit of UVGI. Monitoring and reporting (alarming) when filters reach their recommended pressure drop limitations along with regularly scheduled preventive maintenance will aid in reducing the risk of infections. Proper maintenance and tight-fitting filters are a must. Monitoring through differential pressure sensors to the BAS is a cost-effective method to provide alerts to proper filter maintenance.


Air-handling systems providing air to patient care areas should have interior surfaces that are cleanable, non-eroding, and do not contribute to microbial growth. Consider tight-fitting and sealed casings to prevent unwanted air infiltration and prevent positive pressure air leakage. The components should be arranged to prevent moisture carry-over and have double-sloped drain pans to prevent any standing water or moisture traps. The pan drains should be properly sized, trapped, and installed to allow water to drain properly. Filters and other components need to be accessible and maintainable. Space should be provided between components to allow for cleaning.

Does that sound too easy? Yes, but due to cost constraints, often some of the features are omitted, resulting in lesser quality and certainly less IAQ—and a potential risk of higher future infection rates.

Any new construction or renovation project will require air-moving equipment and ductwork. All equipment should remain clean before and after it arrives on the job site. All ductwork should be sealed from the fabrication shop through the installation to avoid construction dust from entering and contaminating the duct. Air handling systems should be operated only with the scheduled filters in place including all final filters. This action will keep the downstream duct clean and lessen the risks of introducing contaminants upon start-up.

Once systems are operational, a continual program to measure IAQ is necessary to identify and remediate any IAQ issues due to odors, VOCs, airborne pathogens, and other related issues.


The many codes and standards governing healthcare can be confusing. Stepping back and focusing on the goal of maintaining a high IAQ level and minimizing the spread of airborne pathogens through the HVAC system will allow a good, concise design to be established and minimize the potential for increased infections.

Designing and specifying good quality equipment that is cleanable and maintainable, as well as a sustainable system that is reliable and with the appropriate level of monitoring instrumentation, will help meet the goal. It is important to have the owner perform a risk assessment on each project and to implement infection control practices. Collaboration and communication between the HVAC engineer and facility manager along with the rest of the project team play important roles in creating a safe patient care environment.

J. Patrick Banse is senior mechanical engineer with Smith Seckman Reid. He has more than 30 years of experience in the consulting engineering field with the last 25 years in healthcare design and engineering. He is responsible for HVAC, plumbing, and fire protection design for hospital and healthcare projects. Banse is a member of the Consulting-Specifying Engineer editorial advisory board.


ASHRAE. ASHRAE Standard 62.1-2010, Ventilation for Acceptable Indoor Air Quality.

ASHRAE. ASHRAE Standard 52.2-2007, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. 

ASHRAE. ASHRAE Standard 170-2008, Ventilation of Health Care Facilities.

Facility Guidelines Institute. 2010 Guidelines for Design and Construction of Health Care Facilities. 

Memarzadeh, Farhad. The Environment of Care and Health Care-Associated Infections. An Engineering Perspective. ASHE Monograph

Mills, Frank. Indoor Air Quality Standards in Hospitals. Business Briefings: Hospital Engineering & Facilities Management, 2003.