The Occupational Safety and Health Act of 1970 (Public Law 91-596) assures, insofar as possible, safe and healthful working conditions for every working man and woman in the Nation. The act charges the National Institute for Occupational Safety and Health (NIOSH) with recommending occupational safety and health standards and describing exposure concentrations that are safe for various periods of employment, including but not limited to the concentrations at which no worker will suffer diminished health, functional capacity, or life expectancy as a result of his or her work experience. Under that charge and by a 1974 contract, NIOSH and the Occupational Safety and Health Administration jointly undertook the evaluation of sampling and analytical methods for airborne contaminants to determine if current methods met the criterion to produce a result that fell within 25% of the true concentration 95% of the time. In 1995, that protocol was revised. The Components for Evaluation of Direct-Reading Monitors for Gases and Vapors expands the 1995 method development and evaluation experimental testing methods to direct-reading monitors for gases and vapors. It further refines the previous guidelines by applying the most recent research technology and giving additional experimental designs that more fully evaluate monitor performance. This Addendum to the Components document expands the applicability of the Components by presenting methods to be used in evaluating direct-reading monitors for hazard detection in First Responder environments, including those related to incidents involving weapons of mass destruction (WMD). The Addendum contains a standardized test protocol and performance acceptance criteria for evaluating commercially available, direct-reading monitors in a style similar to the Components document. The Components for Evaluation of Direct-Reading Monitors for Gases and Vapors presents methods to be used in evaluating direct-reading monitors for use in workplace compliance determinations. The Addendum contains a standardized test protocol and performance acceptance criteria for evaluating commercially available, direct-reading monitors in a style similar to the Components document."