How critical space testing works in health care

Critical space testing has been shown to be an effective way for health care facility managers to understand and manage the operation of their HVAC systems

By Christopher T. McCarthy and James P. Gleba March 22, 2021


Learning Objectives

  • Understand why critical space testing was established and is important.
  • Define the codes, standards and guidelines that govern the critical space testing.
  • Identify attributes of successful HVAC critical space testing projects.

Air handling systems are integral to the process of properly conditioning the built environment. Air handling units and the systems of which they are a part can be found in all building types and range in size and complexity from basic fan coil units serving hotel rooms, to rooftop AHUs serving office buildings, to large, built-up custom fabricated units serving the pharmaceutical and health care industries.

These systems are essential to keeping occupants cool in the summer and warm in the winter, and they are especially critical to the operation of hospital buildings within the health care system.

Hospitals within the United States health care system are part of a complicated network of facilities that provide some of the best health care services in the world. That care is provided in the community hospitals, academic medical facilities, ambulatory surgery centers and acute care facilities that surround us. Patients of all acuity levels require care and many times complicated medical procedures in these facilities to address their medical condition.

Air handling systems are critical to providing a safe environment for those complicated procedures. The air handling systems in a hospital filter, cool or heat the air that is distributed into the operating rooms, isolation rooms and catheterization labs where these complicated procedures are performed and where the environmental conditions surrounding patients and staff are critical. This environment contributes to the healing process as well.

But how do we know these systems we have come to rely upon and not necessarily think about are providing proper airflow or pressurization, or are operating in accordance with the design intent? Critical space testing verifies performance of the existing systems serving highly acute areas of a hospital.

CST is a maintenance and operations process defined as the measurement of airflow and pressure relationships for spaces that are deemed critical to providing patient care. CST is typically performed within health care facilities and provides facility managers, maintenance personnel, hospital staff and patients confidence in the operation of the heating, ventilation and air conditioning equipment serving operating rooms, isolation rooms and many other critical spaces.

Codes and standards

CST is not a new concept; the integration of CST services into the yearly and sometimes quarterly operations of a health care facility is relatively new. Throughout the past 30 years, evidence has mounted that hospital acquired infections have had a profound impact on patient safety and the healing process within hospital facilities. According to the Centers for Disease Control and Prevention, HAIs account for an estimated 1.7 million infections and 99,000 associated deaths each year.

By some accounts, more than 15% of all HAIs can be attributed to surgical site infections, which occur when microorganisms are released from the surgical team or are introduced through the HVAC system and into the surgical site. These microorganisms are present on microscopic particles such as skin cells, dust particles and respiratory aerosols. Control of the particles and reducing the risk posed by them is one of the important roles of HVAC systems in a health care setting.

Specific to operating rooms but applicable to many other critical spaces within a hospital, maintaining air quality characteristics and pressurization within recommended ranges is essential to controlling both surgical site infections and HAIs.

Over the past 30 years, as health care construction has become more complicated and building codes more integrated into the design process, HVAC systems serving hospital spaces have become more robust. There has been a concerted effort to provide clear direction to engineers and designers regarding air flow, pressurization, temperature and humidity and air exchange criteria.

From 1992 until 2010, the Department of Health & Human Services and the American Institute of Architects published the Guidelines for Design and Construction of Hospital and Health Care Facilities. These guidelines set design criteria for hospital spaces for architects and engineers ranging from recommended minimum room sizes, to finishes, to ventilation rates. Specifically, Table 7-1 within the DHHS/AIA guidelines identified general space types within a hospital and set the specific environmental design criteria.

In 2010, the Facility Guidelines Institute took over publication of the Guidelines for Design and Construction from DHHS/AIA and received support from the ASHRAE, National Institutes of Health and AIA. An important result of the partnership between the Facility Guidelines Institute and ASHRAE was the integration of ASHRAE Standard 170: Ventilation of Health Care Facilities into the 2010 FGI Guidelines for the Design and Construction of health care facilities. ASHRAE 170 replaced the ventilation table (Table 7.1) from the previous editions of the guidelines and became the primary document that identifies the HVAC criteria for ventilation of health care spaces.

With ASHRAE 170 as the published standard, NFPA 99: Health Care Facilities Code adopted in 2012 the FGI guidelines and ASHRAE 170 within its referenced code structure. Soon after, The Joint Commission recognized NFPA 99-2012 and made compliance with it a requirement for accreditation of hospital facilities. Within the health care industry, facilities personnel and health care organizations put forth a great amount of effort into achieving accreditation through The Joint Commission.

Accreditation through The Joint Commission (or other accreditation processes) means a health care organization has met or exceeded the high standards developed for patient safety and high-quality health care and is also required to receive federal payments for Medicare or Medicaid.

As part of the accreditation process, facilities must show they have a documented process to meet The Joint Commission standards that measure and assess the performance of a facility. One of those assessments is defined by The Joint Commission’s Environment of Care 02.05.01. This standard provides measurable definitions for the design and installation of utilities to meet patient care and operational needs. A sub-category of Environment of Care 02.05.01 is defined in an element of performance for the mechanical, electrical and plumbing systems and indicates proper air pressure, filtration and air changes in critical care areas such as the operating room are to be maintained in accordance with NFPA 99 and ASHRAE 170.

The Joint Commission does not provide a specific list of critical spaces to be tested but rather leaves that up to a risk assessment that is to be performed by each health care facility. That risk assessment should define the spaces that each facility deems “critical” due to specific procedures and the risks associated with patient safety. Many facilities specifically test operating rooms, airborne infectious or protective isolation rooms and catheterization labs, but more generally include spaces where air flow, pressure and air exchanges are critical to patient care and safety. This can include central sterile supply, decontamination, soiled utility and clinical labs.

Critical space testing process

Once a facility owner has determined the spaces to be tested, the procedure for testing is straightforward. Almost all testing can be performed by a NEBB– or AABC-certified testing and balancing firm, but there have been instances where hospital facilities staff have performed the task.

A certified air flow hood is used to measure air flow for each supply, return and/or exhaust register in a given space. Pressure testing also is provided at all critical spaces using digital pressure test instrumentation with a greater resolution/accuracy than the local instrumentation. Similar to laboratory testing regimens, care must be taken to avoid measurements where velocities from air distribution system may influence the accuracy of the data.

Room dimensions are used to calculate space area and the ceiling height used to determine room volume. The room volume and measured air flow quantities from the certified flow hood are used to calculate the actual total room air exchanges and that data is compared to the standard in effect at the time of construction.

Where local room pressure monitoring is provided, on-site measurement data is used to confirm the calibration of local displayed data. As the accuracy/stability of local displayed room pressure monitors is influenced by temperature differences between the measured and reference spaces, thermal dispersion-based room pressure measurement devices, which provided extraordinary high levels of accuracy, resolution and stability, should be used.

Minimum ventilation rates are verified with the AHU minimum outdoor air percentages by comparing the required minimum outdoor air exchange rates for each space with the listed minimum outdoor air quantities for the AHUs serving the spaces that were tested. Additionally, calibration of room pressure monitors, room temperature and humidity sensors, supply, return and exhaust air terminal units are verified by comparing measured values with output from the building automation system.

All airflow, humidity and pressure reporting to the facility BAS is verified by comparing actual on-site measurement data for each data point to output from the BAS. All of this information is then provided in a written report documenting each space (see Figure 2).

Key aspects of critical space testing

The process of CST provides many additional benefits besides satisfying the requirements of The Joint Commission, and its importance can be seen in several ways throughout health care organizations.

Many hospitals have grown their physical footprints over the years, typically through the process of expansion and renovation. Renovations may occur consistently, but expansions occur only once every couple of decades. Many hospitals have been developed over multiple building phases and over multiple decades of construction. This can create an antiquated patchwork of HVAC systems serving spaces depending on when the last time an operating room suite or patient floor was renovated. Many spaces in a hospital may have to wait between rounds of renovation for 25 years or longer and, for that reason, the systems installed 25 years ago may still be serving critical spaces in a hospital.

Additionally, it is difficult and expensive to construct in any health care environment and even more so if spaces are renovated in place. As part of the CST process, defining the design intent at the time of construction is an important step in verifying the HVAC system is operating properly.

There are three important aspects of CST:

1. Compliance with original design intent

Mechanical and electrical infrastructure systems — especially HVAC systems from a CST perspective — would have been designed to meet the code or standard that was in effect at the time of design. More importantly, the version it was designed to meet may be different from what is accepted or enforced today. The CST process identifies those critical spaces and provides information on the operation of the HVAC system. Data from the CST process gives a snapshot of the operating condition of the systems and, more importantly, provides that snapshot within the context of when the space was constructed.

It is not reasonable to expect an HVAC system designed for a specific set of criteria 25 years ago to be able to meet current codes and standards. This may be in form of revised air exchange requirements for either total air, ventilation air or for pressurization of a given space as defined in previous editions of the guidelines.

A good example of this is the change in pressurization requirements for endoscopy between the 2001 DHHS/AIA guidelines and the 2014 FGI guidelines. Over the course of four revision cycles, the pressurization requirements were revised four times, rotating between negative pressurization (2001) to no pressurization requirement (2006) to positive pressurization (2010) and back to no pressurization requirement (2014) (see Figure 3).

2. Provide confidence to facilities and c-suite

While the CST process provides confirmation that the existing HVAC system operates in accordance with the original design intent, it also provides confidence to facilities staff, high-level executive staff and users. CST is an independent view of the operation of the HVAC systems and, when performed on a consistent basis, can indicate the systems are operating consistently.

Facilities staff is responsible for the proper operation of the systems. In the case of HVAC systems serving some of the most critical spaces in the hospital, having an independent evaluation of those systems gives facilities staff the information they need to be able to accurately report on system operation. Documenting those conditions and having CST reports readily accessible allows facilities staff to quickly report to all levels management if questions are raised about system operation.

3. Identify deficiencies

One of the most important aspects of the CST process is regarding deficiencies in an existing HVAC system. With the CST process structured to provide information on the operation of an HVAC system, the data provided as part of testing often will show where specify problems reside within a system. If the total air exchanges cannot be met within an operating room, for example, there likely is not adequate supply airflow into the space. Or if proper pressurization cannot be maintained within an airborne infectious isolation room, this most likely points to an issue with the exhaust system. Having regular baseline information is an important tool in troubleshooting systems.

This information can be very important to diagnosing the specific reasons why airflow is not adequate or air exchanges and pressurization requirements cannot be maintained. This should lead to a more thorough review of the HVAC systems serving the spaces and a diagnosis to a potentially larger issue with the systems. It is important to know the issue such that it can be fixed.

Many issues may be able to be resolved through additional balancing of the individual supply, return or exhaust air terminals serving critical spaces. The CST process also may reveal more widespread or complicated issues. These issues are typically specific to AHU operation, automatic temperature controls or overall building pressurization.

Project examples

The CST process is valuable and necessary from a compliance perspective. The initial set up for CST requires an understanding of the HVAC systems before the testing. For many spaces, the basic HVAC layout, taken from existing building drawings, is very useful for both the testing and reporting aspect of CST. The existing HVAC layout overlaid on the existing architectural background provides context for the testing and a reference point for anyone that reviews the report.

That basic understanding of the HVAC layout provided within the report allows facilities personnel to understand the exact systems that are serving a specific critical space. The location of air devices, connecting supply, return or exhaust ductwork as well as volume dampers can also be very useful in troubleshooting any issues that may arise from the testing process. Having that basic understanding of the HVAC system represented in an illustrated format within a final report allows for quick and easy reference for facilities personnel.

The CST process relies on accurate existing conditions and test data to provide reliable information. The required air exchanges referenced in the FGI guidelines provide designers and engineers a means to calculate the required supply, return or exhaust airflow quantities to adequately ventilate a space. This required airflow rate is calculated based on the volume (in cubic feet) of the specific space, a rate of time (measured in hours) and the air exchange rate (air changes per hour).

Figure 6: The diffuser, register and grille sheet provides a summary of all air devices and the associated measured air quantities. Courtesy: Leach Wallace Associates – member of WSP[/caption]

Airflow measurement and testing has been one of the tools used in the construction industry for decades to verify proper operation of HVAC systems. And the introduction of more stringent building codes and standards over the past 10 to 15 years created the need for a process to verify compliance with these more stringent requirements.

Author Bio: Christopher T. McCarthy is a senior vice president with Leach Wallace Associates – member of WSP with more than 35 years of experience in the design of mechanical systems and in the application of CST services for hundreds of health care clients. James P. Gleba is a vice president with Leach Wallace Associates – member of WSP with more than 25 years of experience in the design and application of mechanical systems for hundreds of health care clients.