This Small Entity Compliance Guide (SECG) is intended to help small businesses comply with the Occupational Safety and Health Administration's (OSHA) Respiratory Protection standard (63 FR 1152; January 8, 1998). While the guide is for small entities, the guide itself is not small. OSHA's goal for this document is to provide small entities with a comprehensive step-by-step guide complete with checklists and commonly asked questions that will aid both employees and employers in small businesses with a better understanding of OSHA's respiratory protection standard. The reader should be advised that OSHA also has other shorter documents and visual aids that may be used to better understand respiratory protection and the OSHA standard itself. If the employees of a small business are only exposed to nuisance dusts and relatively non-toxic chemicals and use only a few types of relatively simple respirators, knowledge of the guide and materials supplied by the respirator manufacturer may be sufficient for the small business owner or an employee to become qualified as a program administrator. If more dangerous chemicals or high exposures are present, or sophisticated respirators are used, the program administrator must have more knowledge or experience. In these circumstances, it may be necessary for the administrator to seek out the expertise needed or to obtain appropriate training. OSHA's original Respiratory Protection standard was adopted in 1971 from an existing American National Standards Institute (ANSI) standard. On October 5, 1998, OSHA issued a revised standard that updated and replaced that 1971 standard. The revised 1998 Respiratory Protection standard also included a new provision that allowed the development of new fit tests. In compliance with this provision, OSHA approved and adopted an additional quantitative fit testing protocol, the controlled negative pressure (CNP) REDON fit testing protocol, in 2004. In August 2006, OSHA again revised the standard by adding definitions for APF and MUC and a table of APF values. This guide provides a discussion of these APF provisions and their role in the overall Respiratory Protection standard.