Hospital Planning and Design: Infection Control Measures

1. HVAC System Management

In hospitals, the HVAC system is essential for both comfort and infection control, helping to eliminate airborne contaminants like bacteria, viruses and pollutants. Key control measures include:

Zoning: To prevent cross-contamination, ensure that return air in non-critical areas passes through ceiling plenums with sealed peripheral walls. Ducted returns are mandatory in critical areas with controlled pressure differentials.

Temperature and Humidity Control: Controlled temperature (e.g., 16–20°C in specialised OTs, 20–24°C in general areas, 22–26°C in nurseries and neonatal ICUs) and relative humidity (30–60% in general areas, 20-60% in OTs) minimise microbial growth. Extreme humidity can lead to microbial proliferation or increase airborne particle dispersion.

Air Intakes and Exhaust Outlets: AHU (air handling unit) intakes should be positioned 1.8–3.6m above ground (1m above roof level) and 8m horizontally away from any outdoor contaminant sources. Exhaust outlets should project upward and be positioned at least 3m above roof level, with contaminated air exhausted through a HEPA filter.

Filtration Efficiency: Filters typically combine pre-filters, fine filters, and HEPA (high-efficiency particulate air) filters. Critical areas like ICUs and OTs require higher MERV (Minimum Efficiency Reporting Value) ratings for effective contaminant control. In locations where harmful sulphur compounds are released from nearby large drains or garbage disposal sites, adding chemical filters in AHUs is essential. These filters prevent sulphur-induced pitting of AHU copper pipes and protect sensitive medical equipment, such as CT and PET-CT, from damage. Additionally, chemical filters safeguard patients from exposure to contaminated outdoor air supplied by the AHUs.

Pressure Differential: Positive pressure areas, such as OTs, ICUs, and PE (protective environment) rooms, are designed to prevent contaminants from entering, while negative pressure rooms, like respiratory ICUs and AII (airborne infection isolation) rooms, contain contaminants within. To maintain these pressure differentials, entry and exit doors should be airtight, using hinged or sliding door systems. For example, ICUs should not use non-airtight swing doors, as these can compromise sterility and infection control. Although swing doors enable ease of patient bed movement, infection control measures must take priority. The direction of hinged door opening is also critical: in positive pressure ICUs, the door should open inward, allowing the positive pressure to press the door firmly against the frame, ensuring a proper seal.

Air Change Rate/ Dilution: Increasing the air change rate and fresh air dilution reduces exposure to microorganisms. For instance, in an OT with 20 total ACH (air changes per hour), the time required to remove particles at 99.9% efficiency reduces to 21 minutes compared to 41 minutes at 10 total ACH.

Anterooms: Acting as buffer zones, anterooms reduce airborne contaminants to protect adjacent spaces, such as corridors. These rooms—commonly used in transplant ICU rooms, BMT (bone marrow transplant) patient rooms, PE rooms, AII rooms, chemotherapy preparation rooms and molecular labs—are equipped with supply cabinets, a handwashing sink, and ample space for donning and doffing PPE.

OT Requirements: To meet strict sterility standards, unidirectional laminar airflow is delivered downward from a ceiling-mounted HEPA filter terminal plenum to reduce turbulence. The supply diffuser array should cover an area extending at least 30 cm beyond the operating table footprint on all sides. For effective containment, at least two low sidewall exhaust grilles should be placed at opposite corners, with the lower edge around 20 cm above the floor.

2. Hospital Waste Management

Proper waste management is critical in infection control. Various types of waste—from sharps to contaminated PPE—can pose infection risks if not handled correctly. Key measures include:

Controlled Waste Flow: Hospital design should support unidirectional waste flow, with segregated transport routes for waste and patient areas, and dedicated lifts for waste handling.

Dirty Utility Room Design: In ICU and OT areas, dirty utility rooms should be arranged to prevent waste from crossing paths with patient or clean supply routes. The outer door of the dirty utility room in ICUs should open into the corridor. These rooms may include WCs for disposing of patient fluids to prevent aerosol contamination.

3. Use of Low VOC Materials

VOCs (volatile organic compounds) can cause respiratory irritation and potentially weaken immune responses, increasing susceptibility to infection. Using low-VOC materials, such as carpets, adhesives, paints and furnishings, can improve indoor air quality. While these materials don’t directly control infections, they contribute to a healthier environment.

Conclusion

These infection control measures in HVAC management, waste handling, and material selection are crucial for effective hospital planning and design, creating an environment that prioritises patient health and safety. For detailed department-specific information on temperature, humidity, filtration, pressure differential, and ACH, refer to my recently published book, Handbook of Concept Planning of Hospitals, available on Amazon and Flipkart.