Fire investigation is a required duty for company officers. This requirement is explicitly stated in NFPA 1021: Standard for Fire Officer Professional Qualifications under Fire Officer I job performance requirement 4.5 and in Fire Officer II job performance requirement 5.5.1. The 5.5.1 requirement states "Determine the point of origin and preliminary cause of a fire, given a fire scene, photographs, diagrams, pertinent data, and/or sketches, to determine if arson is suspected so that law enforcement action is taken." An important part of discharging this duty is analyzing the flow, or movement, of fire in a compartment or structure. This analysis has many components, including the flow path, the effects of ventilation availability and fuel availability, and the modern fire environment. This module examines these concepts to help all professionals tasked with determining fire origin and cause better understand fire flow dynamics so they can apply that knowledge to specific incidents. That fire flow knowledge is applicable both to fire investigation and to fire attack. Understanding fire flow can assist in making fire attack decisions, most importantly when and where to vent the building. Venting improperly or at the wrong time can lead to major changes in the fire flow paths, which can have dire consequences for anyone inside the structure.