Detect-to-warn scenarios for defense against airborne contaminants

Detect-to-warn defense strategies against airborne contamination are based on providing warning to personnel to take temporary protective actions. The effectiveness of such detect-to-warn active strategies is measured by the reduction in contaminant exposure compared to passive exposure. Effectiveness depends on several factors, including the contaminant release and transport properties, the warning sensor performance and the protective actions taken. In this paper we analyze effectiveness for several specific scenarios where certain reasonable protective actions are assumed and sensor performance is varied. One type of scenario analyzed is the protection of outdoor personnel against an upwind instantaneous point release. Meteorological conditions such as wind speed, turbulence level and heat flux, which result in high exposure levels are assumed. Personnel are warned to temporarily use filter masks based on a warning signal from a sensor placed between them and the release point. Another type of scenario is the protection of personnel inside of a building using active ventilation control. The building air handling properties, such as air exchange and recirculation, degree of leakage and filtration and zone volume, are representative of modern office buildings. Different sensor locations and ventilation control strategies are chosen to defend against outside and inside instantaneous point releases. In each scenario, we evaluate the dependence of effectiveness on sensor sensitivity threshold and response time. In addition, we describe desired values of other sensor attributes, such as false positive sensing rate, size, power consumption, maintenance frequency and procurement cost, to support realistic deployment and operations.