Engineering Controls

Incorporate appropriate engineering controls to reduce potential risk to patients and office personnel via aerosol exposure of SARS‑CoV‑2.2

CDC does not provide guidance on the decontamination of building heating, ventilation, and air conditioning (HVAC) systems potentially exposed to SARS‑CoV‑2. To date, CDC has not identified confirmatory evidence to demonstrate that viable virus is contaminating these systems. CDC provides the following recommendations for proper maintenance of ventilation systems and patient placement and volume strategies in dental settings.

  • Properly maintain ventilation systems.
    • Ventilation systems that provide air movement in a clean-to-less-clean flow direction reduce the distribution of contaminants and are better at protecting staff and patients. For example, in a dental facility with staff workstations in the corridor right outside the patient operatories, supply-air vents would deliver clean air into the corridor, and return-air vents in the rear of the less-clean patient operatories would pull the air out of the room. Thus, the clean air from the corridor flows past the staff workstations and into the patient operatories. Similarly, placing supply-air vents in the receptionist area and return-air vents in the waiting area pulls clean air from the reception area into the waiting area.
    • Consult a HVAC professional to investigate increasing filtration efficiency to the highest level compatible with the HVAC system without significant deviation from designed airflow.
    • Consult a HVAC professional to investigate the ability to safely increase the percentage of outdoor air supplied through the HVAC system (requires compatibility with equipment capacity and environmental conditions).
    • Limit the use of demand-controlled ventilation (triggered by temperature set point and/or by occupancy controls) during occupied hours, and when feasible, up to 2 hours post occupancy to assure that ventilation does not automatically change. Run bathroom exhaust fans continuously during business hours.
    • Consider the use of a portable HEPA air filtration unit while the patient is actively undergoing, and immediately following, an aerosol-generating procedure.
      • Select a HEPA air filtration unit based on its Clean Air Delivery Rate (CADR). The CADR is an established performance standard defined by the Association of Home Appliance Manufacturers and reports the system’s cubic feet per minute (CFM) rating under as-used conditions. The higher the CADR, the faster the air cleaner will work to remove aerosols from the air.
      • Rather than just relying on the building’s HVAC system capacity, use a HEPA air filtration unit to reduce aerosol concentrations in the room and increase the effectiveness of the turnover time.
      • Place the HEPA unit near the patient’s chair, but not behind the OHCP. Ensure the OHCP are not positioned between the unit and the patient’s mouth. Position the unit to ensure that it does not pull air into or past the breathing zone of the OHCP. The use of these units will reduce particle count (including droplets) in the room and will reduce the amount of turnover time, rather than just relying on the building HVAC system capacity.
    • Consider the use of upper-room ultraviolet germicidal irradiation (UVGI) as an adjunct to higher ventilation and air cleaning rates.15
  • Patient placement
    • Ideally, dental treatment should be provided in individual patient operatories whenever possible.
    • For dental facilities with open floor plans, to prevent the spread of pathogens there should be:
      • At least 6 feet of space between patient chairs.
      • Physical barriers placed between patient chairs. Easy-to-clean floor-to-ceiling barriers enhance effectiveness of portable HEPA air filtration systems (verify that extending barriers to ceiling will not interfere with fire sprinkler systems).
      • If possible, operatories should be oriented parallel to the direction of airflow.
    • Where feasible, consider patient orientation carefully, placing the patient’s head near the return air vents, away from pedestrian corridors, and towards the rear wall for vestibule-type office layouts.
  • Patient volume
    • Ensure to account for the time required to clean and disinfect operatories between patients when calculating your daily patient volume.
      • Once the patient has left the room, OHCP (including environmental services personnel) should refrain from entering the vacated room used to treat suspected or confirmed patients with COVID‑19 until sufficient time has elapsed for enough air changes16 to remove potentially infectious particles. After this time has elapsed, the room should undergo appropriate cleaning and surface disinfection before it is returned to routine use.
        • Parameters to consider in determining the time necessary to remove potentially infectious particles include: room air flow rate; use of HEPA air filtration devices; length of aerosol-generating procedures; and use of isolation and high-volume evacuation devices.17
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