7.3 Air Quality Controls, HVAC Systems & Construction ICRA

7.3 Air Quality Controls, HVAC Systems & Construction ICRA

Heating, Ventilation, and Air Conditioning (HVAC) systems in healthcare facilities are sophisticated engineering controls designed to maintain indoor air quality, control environmental temperature and humidity, and prevent the transmission of airborne pathogens. Inadequate ventilation, compromised filtration, or unmitigated construction dust can lead to severe healthcare-associated outbreaks of fungal infections (such as invasive aspergillosis) or airborne viral and bacterial diseases. Infection Preventionists (IPs) must master healthcare HVAC engineering standards, directional airflow dynamics, and the Infection Control Risk Assessment (ICRA) process for construction and renovation.

Healthcare HVAC System Engineering Standards

The Facility Guidelines Institute (FGI) and ASHRAE Standard 170 (Ventilation of Health Care Facilities) mandate stringent environmental parameters for clinical spaces. Key ventilation variables include:

• Air Changes per Hour (ACH): ACH measures the volume of clean air supplied to or exhausted from a space per hour divided by the room volume. High ACH rates dilute and remove airborne bioaerosols rapidly. For example, a room with 12 ACH removes approximately 99% of airborne contaminants within 23 minutes, and 99.9% within 46 minutes.
• Relative Humidity (RH): Healthcare environments must maintain relative humidity between 30% and 60% (or 20%–60% depending on specific clinical guidelines). Excessively low humidity (<30%) causes mucosal drying in patients and staff, increasing susceptibility to respiratory infection, and increases static electricity. Excessively high humidity (>60%) promotes fungal growth, mold proliferation in wall cavities, and dust mite survival.
• Temperature Control: Clinical area temperatures are typically maintained between 68°F and 75°F (20°C–24°C). Operating rooms (ORs) are often maintained cooler (62°F–68°F / 17°C–20°C) to accommodate surgical attire, reduce surgeon perspiration, and meet specialized surgical protocol requirements.

Directional Pressure Differentials & Specialized Patient Rooms

Controlling air pressure differentials between adjacent spaces directs air movement from clean areas to dirty areas, preventing the spread of airborne contaminants.

Airborne Infection Isolation Rooms (AIIR)

AIIRs are engineered to isolate patients with confirmed or suspected airborne infectious diseases, such as Mycobacterium tuberculosis, measles (rubeola) virus, varicella-zoster virus (chickenpox/disseminated shingles), and smallpox or novel bioaerosol threats (e.g., SARS-CoV-2 during aerosol-generating procedures).

• Negative Pressure: Air pressure in an AIIR is lower than in the adjacent anteroom or corridor (pressure differential ≥2.5 Pascals or 0.01 inches water gauge). When the door opens, air flows into the AIIR, preventing pathogens from escaping into public hallways.
• Air Handling: Requires a minimum of 12 ACH for new construction. Room air must be exhausted directly to the outside of the building away from air intakes and populated areas, or passed through a HEPA filter prior to recirculation.
• Monitoring: Continuous visual pressure monitoring devices (e.g., electronic manometers, ball-in-tube indicators) are required, supplemented by daily manual tissue/smoke tests when occupied.

Protective Environments (PE)

Protective Environments protect severely immunocompromised patients—such as allogeneic hematopoietic stem cell transplant (HSCT) recipients—from ubiquitous environmental fungal spores, primarily Aspergillus species.

• Positive Pressure: Air pressure in a PE room is higher than in adjacent corridors (pressure differential ≥2.5 Pa / 0.01 inches water gauge). Air flows outward from the room, preventing un-filtered corridor air from entering.
• Filtration: Supply air entering a PE room must pass through High-Efficiency Particulate Air (HEPA) filters (≥99.97% efficiency for 0.3-micron particles). PE rooms require positive pressure, ≥12 ACH, and smooth, easily cleanable non-porous surfaces.

Air Filtration & HEPA Specifications

Air filtration systems in healthcare facilities utilize multi-stage filter banks:

• Pre-Filters (MERV 8–13): Capture large particulate matter, dust, and lint to protect downstream heating/cooling coils and high-efficiency filters.
• HEPA Filters: True HEPA filters demonstrate a minimum efficiency of 99.97% in capturing particles as small as 0.3 microns in diameter. This 0.3-micron size corresponds to the Most Penetrating Particle Size (MPPS); particles smaller or larger than 0.3 microns are trapped with even higher efficiency due to impaction, interception, and Brownian diffusion. HEPA filters must undergo annual in-situ challenge testing (using dioctyl phthalate [DOP] or polyalphaolefin [PAO] aerosols) to verify filter media integrity and housing seals.

Construction & Renovation Infection Control Risk Assessment (ICRA 2.0)

Demolition, structural wall penetration, and ceiling removal generate massive quantities of dust containing Aspergillus spores and environmental bacteria. Inhalation of construction dust by vulnerable patients can lead to fatal invasive pulmonary aspergillosis. To mitigate this risk, IPs conduct an ICRA prior to initiating construction.

The ICRA 2.0 matrix evaluates work scope against patient risk to assign mandatory containment classes:

1. Step 1: Construction Activity Type:
   • Type A: Non-invasive inspection, paint touching, minor electrical work without wall cutting.
   • Type B: Small-scale, short-duration work generating minimal dust (e.g., cutting walls for minor plumbing/cabling).
   • Type C: Work generating moderate to high dust levels or requiring demolition of fixed building components (e.g., wall removal, ceiling tile replacement in large areas).
   • Type D: Major demolition, structural modification, and building renovation projects.
2. Step 2: Patient Risk Group:
   • Group 1 (Low Risk): Non-patient care areas (offices, mechanical rooms).
   • Group 2 (Medium Risk): Outpatient clinics, physical therapy, general admission wards.
   • Group 3 (High Risk): Emergency department, intensive care units, pediatrics, surgical suites.
   • Group 4 (Highest Risk): Oncology, BMT units, organ transplant wards, cardiac catheterization labs, Protective Environments.
3. Step 3: ICRA Control Class Matrix: Combining Construction Type and Patient Risk determines ICRA Precautions (Class I through Class V).

Mandatory Engineering Controls for High-Class ICRA (Class IV & V)

• Rigid Barriers: Installation of dust-tight, airtight containment barriers (6-mil flame-retardant poly or rigid drywall/plastic panels) extending from true floor to true ceiling slab prior to work initiation.
• Negative Air Machines (NAMs): Continuous operation of portable HEPA-filtered negative air machines within the construction zone, maintaining negative pressure relative to surrounding clinical areas (≥-0.02 inches water gauge) and exhausting outside the building envelope.
• Anterooms & Walk-Off Mats: Constructing anterooms for worker clothing changes, vacuuming, and equipment decontamination. Sticky walk-off mats placed at anteroom exits.
• Debris Containment: Transporting construction debris in covered, sealed carts along pre-designated transit routes during off-peak hours.