Explosions

An explosion is a rapid release of energy that causes the abrupt expansion of gases, producing a high-pressure shock wave, heat, and often debris. Explosions arise from chemical reactions, physical phase changes, or nuclear processes. In chemical explosions, rapid oxidation releases energy in a short time. In deflagration, the reaction is subsonic; in detonation, a supersonic, shock-driven process yields higher overpressure. Nuclear explosions release energy by fission or fusion, generating extreme overpressures and intense thermal radiation. Some industrial processes, such as rapid steam generation or phase changes, can produce explosive effects without chemical reactions, though these are less common.

Explosions are categorized by energy release mechanism and scale. Low-order chemical explosions include blasting charges used in mining and demolition. Dust, gas-air, and vapour cloud explosions are accidental or uncontrolled. In industrial and military contexts, controlled demolitions and propulsion tests also occur. For safety and risk assessment, peak overpressure, impulse, and blast duration are considered, along with secondary effects such as flying debris, thermal radiation, and ground shock.

The effects of explosions depend on size, type, and environment. The blast wave can cause structural damage, shrapnel injuries, and thermal injuries. Protective design uses metrics such as TNT equivalent and scaled distance to estimate potential damage and required protections. Emergency response focuses on damage assessment, casualty care, and securing the area.

Measurement and safety include expressing energy as TNT equivalent, using peak overpressure and impulse to characterize effects, and applying scaled distance to compare scenarios. Protective design and zoning aim to reduce risk, while regulations govern handling of energetic materials. Emergency response emphasizes scene control, first aid for blast victims, and coordination among responders.