Air Quality Monitoring During High-Level Biocontainment Ground Transport: Observations From Two Operational Exercises

Abstract

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.

Keywords: Ebola virus disease; air quality; biocontainment; emergency medical services; transport isolator.

Figure 1.

Flow diagram of modeled losses and gains of CO₂ and H₂O to the air within the isolator from inhalation, exhalation, perspiration, and ventilation and with operation of the isolator’s blower.

Figure 2.

Measured and modeled environmental parameters and clinical monitoring data obtained during the transport exercise from St. Louis, MO to Iowa City, IA. The volunteer was enclosed within the isolator just prior to the start of data collection.

Figure 3.

Measured and modeled environmental parameters from the L.A. County stationary exercise. The volunteer was enclosed within the isolator just prior to the start of data collection.

Figure 4.

Measured and modeled environmental parameters from a simulated blower failure. The subject entered the isolator at 9:17 PM (with running blower, yellow shading), the blower was turned off at 9:52 PM for ten minutes (red shading), and then the blower was turned back on at 10:02 PM (yellow shading).