Air Quality Monitoring during High-Level Biocontainment Ground Transport: Observations from Two Operational Exercises

Objective: Stretcher transport isolators provide mobile, high-level biocontainment outside the hospital for patients with highly infectious diseases, such as Ebola virus disease. Air quality within this confined space may pose human health risks. Methods: Ambient air temperature, relative humidity, and CO2 concentration were monitored within an isolator during 2 operational exercises with healthy volunteers, including a ground transport exercise of approximately 257 miles. In addition, failure of the blower unit providing ambient air to the isolator was simulated. A simple compartmental model was developed to predict CO2 and H2O concentrations within the isolator. Results: In both exercises, CO2 and H2O concentrations were elevated inside the isolator, reaching steady-state values of 4434 ± 1013 ppm CO2 and 22 ± 2 mbar H2O in the first exercise and 3038 ± 269 ppm CO2 and 20 ± 1 mbar H2O in the second exercise. When blower failure was simulated, CO2 concentration exceeded 10 000 ppm within 8 minutes. A simple compartmental model predicted CO2 and H2O concentrations by accounting for human emissions and blower air exchange. Conclusions: Attention to air quality within stretcher transport isolators (including adequate ventilation to prevent accumulation of CO2 and other bioeffluents) is needed to optimize patient safety.