This module, one of 25 on vocational education training for careers in environmental health occupations, contains self-instructional materials on using air-purifying respirators. Following guidelines for students and instructors and an introduction that explains what the student will learn are three lessons: (1) describing how air flows through an air-purifying respirator, and disassembling a respirator and telling how each part works; (2) cleaning and inspecting each part of the respirator, and reassembling it for storage and use; and (3) fitting a respirator so it makes a proper seal on one's face, and testing that fit using various types of qualitative fit tests. Each lesson contains objectives, recommended methods and locations for practice, performance criteria, equipment and supplies to perform a task, detailed step-by-step instructions for learning a task, and performance exercises. Two performance tests cover cleaning, inspecting, and reassembling of dual-cartridge, air-purifying respirators; and performing qualitative fit tests. (CT)