Project Summary Phosgene is essential to the manufacturing of products used in everyday life such as flexible foams, thermoplastic polyurethane, and sealants and elastomers. It is also a building block for many plastics, pesticides, and pharmaceuticals. However, at room temperature phosgene is an extremely toxic, colorless gas—exposure can cause immediate symptoms of eye and skin irritation, and symptoms of respiratory distress such as coughing, tightness in the chest, difficulty breathing, pneumonia, or heart failure that may not manifest until 6-24 hours after exposure. Therefore, phosgene-producing facilities need large phosgene detectors for wide-area monitoring, as well as phosgene indicator badges for monitoring individuals. Electrochemical detectors perform real-time monitoring with audio alarms for phosgene exposure, but they are expensive and can only be installed in limited locations. A wearable colorimetric indicator badge is the standard means of monitoring individuals. It indicates the presence of phosgene by changing color, but the disadvantage is that the worker must constantly look at the badge to ensure their personal safety because it does not actively alert them to danger. Intelligent Optical Systems, Inc. (IOS) proposes to develop a low SWaP (size, weight, and power), low-cost wearable phosgene sensor for individuals that will incorporate a highly selective colorimetric phosgene sensor film with a highly sensitive optical readout unit that will trigger an audible alarm when the worker is exposed to phosgene levels that exceed a set threshold.