Most fire deaths are caused not by flames, but by smoke. Toxic gases and loss of visibility disable occupants long before fire reaches them — which is exactly why predicting how smoke and heat move through a building is one of the most valuable things a fire safety engineer can do. The best tool for that job is free, open source, and built by the US government: FDS — the Fire Dynamics Simulator . This guide explains what FDS is, its capabilities and application areas, how any user can get started, and how it helps prevent fire disasters in buildings. Figure 1. What FDS models: a fire generates a rising thermal plume, hot smoke banks down under each ceiling, and occupants must escape before visibility and temperature become untenable. FDS predicts these smoke and heat flows hour by second across the whole building. Table of Contents What Is FDS (Fire Dynamics Simulator)? Capabilities of FDS Application Areas Smokeview, BlenderFDS & Companion T...
Buildings account for roughly a third of global energy use , and as net-zero targets tighten, building energy simulation has moved from a specialist afterthought to a core design discipline. The good news: the most accurate and widely trusted tools in this field are free and open source , led by the US Department of Energy's own simulation engine. This guide reviews the top open source building energy simulation tools in 2026 , covering the engines, the interfaces that make them usable, and which tool fits each stage of design. Figure 1. What building energy simulation models: solar heat gains striking the facade, heat flowing between colour-coded thermal zones, and losses through the envelope. Open source engines like EnergyPlus resolve these flows hour by hour across a full year. Table of Contents Why Open Source Building Energy Simulation? 1. EnergyPlus 2. OpenStudio 3. Ladybug Tools (Honeybee) 4. ESP-r 5. Modelica Buildings Libra...