The report, discussing phosgene, is one of a series addressing the prevention of accidental releases of toxic chemicals. Phosgene, a highly reactive and corrosive liquid that boils at room temperature, has an Immediately Dangerous to Life and Health (IDLH) concentration of 2 ppm, which makes it a substantially acute toxic hazard. Reducing the risk associated with an accidental release of phosgene involves identifying some of the potential causes of accidental releases that apply to processes that use phosgene. The manual identifies examples of potential causes and measures that may be taken to reduce the accidental release risk. Such measures include recommendations on plant design practices, prevention, protection, and mitigation technologies, and operation and maintenance practices. Conceptual cost estimates of possible prevention, protection, and mitigation measures are provided.