This guide contains information about 69 items of respiratory personal protective equipment (PPE) for the emergency first responder. This guide was created in partnership with the National Institute of Justice in order to assist with the selection of chemical and biological defense equipment for emergency workers. This volume of the guide, Volume IIa, deals specifically with respiratory PPE. This guide series begins with Volume I, which serves as an information source for all PPE, and then progresses through Volumes IIa, IIb, and IIc, which each focus on a particular area of PPE. The introduction explains that the long range plans for defense include the evaluation of existing PPE and the development of a series of documents, including user guides, national standards, and technical reports related to PPE. Since the evaluation process will take several years this guide was developed in the interim to assist emergency workers in the selection of commercial PPE. The information contained herein was compiled through literature searches and market surveys. The purpose of the guide is to provide information about PPE items to emergency workers, not to make specific recommendations about items. Detailed information about particular items of respiratory PPE is offered in this volume, including stock number, manufacturer, and certifications for the items.