Why indoor air quality matters in hospitals

A properly designed and maintained HVAC system can directly affect the indoor air quality in a hospital or health care setting

By Greg Wittek April 13, 2023
Courtesy: Harris


Learning Objectives

  • Learn why IAQ is important in hospitals and health care facilities.
  • Understand the impact of proper maintenance and cleaning.
  • Learn how both negative and positive pressure rooms are used in patient care.

IAQ insights

  • Indoor air quality (IAQ) can be controlled with various components of the HVAC system.
  • In a hospital setting, IAQ must meet certain codes and standards set by ASHRAE or other governing bodies.

It should come as no surprise that a hospital’s mechanical design requirements and heating, ventilation and air conditioning (HVAC) system maintenance procedures are typically more complex than in other facilities. Indoor air quality (IAQ), air conditioning, ventilating systems and other facets of HVAC systems and control matter greatly. Not only do they make a difference in maintaining comfortable climate conditions and humidity levels in hospitals and other health care facilities, but also help maintain a clean environment so patients, staff and other occupants are not harmed and medical equipment functions properly.

Infectious diseases can travel via airborne particles. The size and velocity of those particles, along with the surrounding airflow, all impact their spreading behavior. Poorly (or irregularly) maintained systems can cost hospitals millions due to improper service, repair shutdowns or equipment failures.

Hospital systems must consistently function at top capacity and be in pristine condition. Systems that are not properly cleaned, sanitized and proactively serviced can exacerbate health problems for people with allergies, respiratory health conditions or autoimmune disorders, as well as cause infection or introduce pathogens into critical spaces such as operating rooms (ORs).

Investing in regular, proper maintenance is necessary to reduce health risks and lost time. Preventive service programs specifically designed to help medical facilities and other critical environments can help reduce the risk associated with IAQ. The presence of pathogens or bio-growth can be limited with regular, consistent cleaning methods using proper medical-grade HEPA filtration and fungicides. According to the Environmental Protection Agency, HEPA filters must remove 99.97% of allergens such as mold, bacteria, dust, pollen and any other particles that are 0.3 microns or larger.

Figures 1 and 2: It is critical to enlist an HVAC service expert who follows standards focused on risk control for hospital HVAC cleaning, using biodegradable EPA-registered fungicides and biocides that kill 99.9% of pathogens and help prevent organic growth within air handling units. Courtesy: Harris

IAQ is affected by AHU coils

Health care facility requirements demand very high quantities of outside air along with significant treatment of the ventilated air, which includes cooling, dehumidifying, reheating, humidifying and filtration. This impacts energy efficiency and use. In fact, according to ASHRAE, the health care sector is one of the largest segments in the U.S. economy with the average hospital using 2.5 times the amount of energy as other commercial buildings.

Isolation rooms, for instance, use more energy but are a necessity when it comes to IAQ. In certain cases, a patient must be isolated in a room designed specifically to reduce the transmission of airborne infectious pathogens and/or contaminated droplets. Rooms used for isolation are considered either Airborne infection isolation with a negative-pressure differential to the adjacent anti-room/area or protective environment with a positive-pressure differential such as an OR. Each plays a unique role and must be engineered appropriately.

Uniform design requirements, standards and technical criteria exist for all rooms whether negative or positive. A negative isolation room may only have one patient bed, a dedicated bathroom for the patient (so they are not exposed to the general public), door sweeps, self-closing doors and a slew of other specific requirements.

Notable industry resources on requirements and standards for negative or positive pressure rooms are ASHRAE Standard 170: Ventilation of Health Care Facilities, the Guidelines for Design and Construction of Inpatient Facilities by Facility Guidelines Institute (FGI) and the National Institutes of Health Design Requirements Manual.

Specific attributes of negative and positive pressure rooms include:

Airborne infection isolation (negative pressure):

  • Have negative air pressure in relation to all adjacent spaces.

  • Exhaust cubic feet per minute (cfm) is greater than supply cfm.

  • Prevent contagious pathogens (such as tuberculosis, COVID-19 or flu) from escaping the room and infecting others.

  • Minimize levels of contagion within the room due to high air-change rates.

Protective environment (positive pressure):

  • Have positive air pressure in relation to all adjacent spaces.

  • Supply more air into the protective environment than is returned so no contaminants should enter.

  • Protect patients with weakened immune systems.

How pressure affects IAQ

Whether providing for negative or positive pressure, additional systems and components should be considered for an isolation room to effectively provide patient and caregiver protection. For one, a minimum of 12 air changes per hour must be maintained to sustain the desired environment. Depending on the room size and purpose, more may be necessary. The room also must maintain a minimum -0.01 inch water column (negative pressure) or + 0.01 inch water column (positive pressure) differential pressure.

It is important to note that testing, adjusting and verification of room air changes and outside air exchanges is required in all health care facilities. Rooms must also be well sealed to prevent excess air from leaking in or out. This includes adequately sealing self-closing entryways, floors, walls and windows. The tighter the room is constructed, the more efficiently the air pressure differential can be maintained.

Figure 3: Diagram of a negative pressure isolation room. Courtesy: Harris

Figure 4: Diagram of a positive pressure isolation room. Courtesy: Harris

Each isolation room is also required to have a permanently installed visual device or mechanism to constantly monitor air pressure relationships. The most reliable way to monitor room pressure is with an electronic pressure monitor, which when properly selected and installed, can provide continuous confirmation of the required pressure differential across the room boundary.

When it comes to designing mechanical systems for isolation rooms, consider the required airflow to maintain the proper pressure differential, equipment location, equipment redundancy and the ability to service the equipment. As mentioned, energy use is a factor. This 2021 U.S. Department of Energy report provides an overview of the current literature on occupant health-related issues concerning health care facilities in the context of energy efficiency.

Controlling the spread of airborne infectious diseases is a serious concern for hospital patients, staff and visitors. Proper maintenance, correct filtration and the appropriate design of isolation rooms should all be top of mind.

Author Bio: Greg Wittek, CHC, is a senior project manager at Harris. He has more than 20 years of industry experience, which includes extensive health care project management experience, in addition to other market segments.