Emergency Medical Services often transport patients with suspected/confirmed airborne
diseases such as Mycobacterium tuberculosis. These pathogens are contagious and have
potential to remain suspended in the air for extended periods of time. The timeframe
for pathogen removal by airing out ambulances is not well defined. This study evaluates
the time required to effectively remove these airborne pathogens from ambulances by
determining the air changes per hour (ACH).
We measured the ACH in twenty ambulances of various models using the concentration
decay method with carbon dioxide (CO2) as a tracer gas. Individually, we evaluated
the relationship between temperature, humidity, volume, and air exhaust velocity with
ACH. Linear regression was used to measure the line of best-fit for CO2 concentration
over time, where the gradient of the line represented ACH for each ambulance tested.
Environmental factor influence was examined by correlation coefficients with an alphaapt-ent-b
202F apt-ent-e apt-ent-uapt-ent-b 003D apt-ent-e = apt-ent-uapt-ent-b 202F apt-ent-e
apt-ent-u0.05. Statistical analyses were performed using R version 3.6.1.
Under the conditions studied, the measured air change per hour ranged from 14.62 to
40.9 ACH. Using the Centers for Disease Control and Prevention guidelines for airborne
contaminant removal by 99.9apt-ent-b 0025 apt-ent-e % apt-ent-u efficiency, the amount
of time required to air out ambulances based on maximum and minimum measured ACH is
21 and 35 minutes respectively. Changes in humidity, volume, temperature, and exhaust
velocity all demonstrated significantly weak relationships with ACH (r < 0.2, p <
This study found that the CO2 concentration decay method can be used to determine
ACH, which is necessary to determine the amount of time required to effectively remove
airborne pathogens in an ambulance. This study shows that 21-35 minutes is an effective
timeframe to air out the ambulances. Environmental factors have a weak relationship
with ACH and therefore is a relatively unimportant factor in air out timeframe.