In March 1999, the National Institute for Occupational Safety and Health (NIOSH) cosponsored a Chemical and Biological Respiratory Protection Workshop with the Occupational Safety and Health Administration (OSHA) and the Department of Defense, U.S. Army Research, Development and Engineering Command (RDECOM). The objectives of this meeting were to: (1) identify and understand the hazards associated with a terrorist chemical and biological incident, (2) identify the different civilian responders and their respiratory protections needs, (3) determine which respirators and selection criteria are currently being used for response to these incidents, and (4) determine public and medical community concerns that must be considered in developing standards for chemical and biological respiratory protective devices. NIOSH began collaborating with the National Institute of Standards and Technology (NIST), OSHA and RDECOM, which includes Edgewood Chemical Biological Center (ECBC) and Natick Soldier Center (NSC), to address the concerns identified at the workshop, and to discuss the development of standards for emergency first responder respiratory protection. In April 2001, NIOSH held a public meeting on developing and implementing standards for chemical, biological, radiological and nuclear (CBRN) respiratory protective devices. At the meeting it was announced that actual military chemical warfare agents (CWA) would be used in future NIOSH certification testing of CBRN respiratory protective devices. Sarin (GB) and sulfur mustard (HD) had been chosen as representative CWA in their categories. Respirator and other personal protective equipment (PPE) manufacturers requested that NIOSH identify chemical compounds that could be used as test simulants in lieu of GB and HD. These manufacturers expressed an interest in using CWA simulants for in-house material and product development testing and to pretest their respirator systems for CWA agent permeation resistance. Manufacturers do not have access to CWA to perform testing and there are a limited number of certified laboratories able to perform CWA testing because of the high cost, toxicity, and the extensive regulatory controls. This makes any type of CWA testing very expensive and inconvenient as a result of the required lead-time.