FPETOOL is a computerized package of relatively simple engineering equations and models. FPETOOL consists of a pacakage of engineering tools useful in estimating potential fire hazard and the response of the space and fire protection systems to the developing hazard. To a large extent, user instructions are included as screen messages presented at the time of need by FPETOOL. This document covers information useful to the user, but not included as screen messages. A separte report, FPETOOL, Fire Protection Engineering Tools for Hazard Estimation (NISTIR 4380), also is available.