---
name: ferret-physics-combustion-explosions
description: Use for burning and blasting in Ferret: combustion chambers, guns, rockets, piston engines, jets and boilers; blast waves by scaled distance, shielding, craters, casings that throw fragments, armour, and vessels that burst. detonate, fireGun, nozzle, blastAt, craterRadius.
---

# Combustion and explosions

## When to use
A gun, a rocket, an engine, a boiler that can burst, a grenade, a crater, danger rings for a charge.

## The model
`combustion` models burning in a closed space and using the pressure: chambers, guns (`fireGun`), rockets (`nozzle`), engines, jets, boilers. `explosions` turns energy into blast: overpressure and impulse by scaled distance (`blastAt`, `radiusFor`), shielding by bodies, fragments and spall from a `Casing`, `armour` that stops them, craters (`craterRadius`, `CraterLaw` per soil), and vessels that burst (`vesselTnt`). Bodies get impulse `I · A`.

## Steps
1. Enable `explosion` (and `strength` if bodies must break; `terrain` for craters).
2. `detonate({ at, tnt })` or `{ vessel: { pressure, volume, gamma }, burst, casing, seed }`.
3. Shield by putting a body between; set `transmission`; walls break by `rupture`.
4. Guns and rockets: build the spec, fire, read `peakPressure`, `muzzleVelocity`; hand a burst's pressure and volume to `detonate`.
5. Commands: `explosion.detonate|info|preview`, `chamber.ignite`, `gun.fire`, `engine.start`.

## Check afterwards
Eight times the charge gives twice the radius; rocket thrust rises with altitude by `Δp_a · A_e`; a barrel rated below peak pressure bursts.

## What usually goes wrong
- Nothing moves: below `minPressure` at that distance, or shielded.
- Nothing breaks: `rupture` is `Infinity` by default.
- Wrong crater: no terrain, an `air` burst, or soil missing from `craters`.
- `ignite()` false: outside flammability limits, no oxygen or fuel.
- Different fragments each time: pass a `seed`.

## Files

- `reference/combustion.md` — Burning in a closed space and using the pressure: guns, rockets, petrol and diesel engines, jets, boilers and gas cylinders that burst.
- `reference/explosions.md` — Blast waves, shielding, craters, casings that throw fragments, armour that stops them, and vessels that burst.
- `reference/api-physics-combustion.md` — every export of `@ferret/physics-combustion` with signature and doc comment
- `reference/api-physics-explosions.md` — every export of `@ferret/physics-explosions` with signature and doc comment
- `reference/commands.md` — 11 commands of these packages with their arguments
- `recipes/blasts-and-ground.md` — Seven recipes: danger rings, a crater in sand and in rock, a charge buried too deep, a crater in a real terrain, a wall that shields, an underwater burst, a trench that holds or slumps.
- `recipes/tank-fire.md` — A fire heats a sealed tank, the gas inside warms and its pressure climbs, the shell gives way and the tank becomes a blast with fragments that push a crate. Heat, links, gas, explosions and bodies in one loop.