Trust but verify-Advanced Methods for Determining Critical Ventilation Efficacy

Background:

Ventilation standards in health care are intended to provide comfort and infection control for at risk patients and employees.  Standard ventilation test and balance methods do not effectively demonstrate air mixing which provides area analysis for infectious particle management.  Additionally, traditional air test and balance services are often performed prior to occupancy when certain furnishings, instrumentation and ancillary equipment are not installed. These items can affect the effective air exchange within the room.
Objective:

Validation parameters for special ventilation rooms (Operating, Airborne Infection Isolation and Protective Environment) rooms will determine design criteria meet particle removal requirements for infection control safety in an “existing” conditions of a patient care area. 
Methods:

When particles are generated with a DeVilbis aerosol generator using 0.9% normal saline the saline release creates droplet nuclei, which can be studied for transit time (age of air) movement of particles and air exchange determinations.  This information helps demonstrate movement from the source of particles to the extraction point in the special ventilation room.  These data along with particle removal rates demonstrate the ventilation efficacy of the specified area.
Twenty-two different rooms either PE or OR were evaluated for particle removal and transit time. Ventilation parameters were determined for each room-type. Prior to release of particles exhaust ventilation velocities were recorded at exhaust grilles, supply air configuration was noted and relative room pressure was recorded. The particles were detected using two optical particle counters placed by the return/exhaust grills in respective rooms.  The particles were released using pressurized air for 60 seconds. The initiation of the aerosol was timed. When a 10% increase in particle concentration was noted over background that transit time was recorded.  Then the extractors were temporarily blocked and particles allowed to buildup for 5 minutes.  When blockage was removed the slope of the decay would serve as a test for air exchange rate using log-normal analysis of time interval and particle concentration.
Results:
Transit times ranged in operating rooms from 16 to 120 seconds depending on amount of clutter and extractor distance from source of aerosol. Effective air exchange is compared to traditional test and balance data for verification purposes. 
Conclusions:
This analysis will allow for testing of special ventilation airflow to determine the efficacy of the ventilation.  This type of evaluation can demonstrate effects of clutter in special ventilation rooms that block free flow of air, and a cost effective method to assess or validate “as operating” air exchanges.  Such infection control ventilation verification will help rule out ventilation as a source of certain infections.