Biological warfare agent (BWA) detectors are designed to provide alerts to military personnel of the presence of dangerous biological agents. Detecting such agents promptly makes it possible to minimize contamination and personnel exposure and initiate early treatment. It is also important, though, that detectors not raise an alarm when the situation does not warrant it. The question considered in this book is whether Agent-Containing Particles per Liter of Air (ACPLA) is an appropriate unit of measure for use in the evaluation of aerosol detectors and whether a better, alternative measure can be developed. The book finds that ACPLA alone cannot determine whether a health threat exists. In order to be useful and comparable across all biological agents and detection systems, measurements must ultimately be related to health hazard. A Framework for Assessing the Health Hazard Posed by Bioaerosols outlines the possibility of a more complex, but more useful measurement framework that makes it possible to evaluate relative hazard by including agent identity and activity, particle size, and infectious dose.