The words of fire,
in plain language.
Short, clear definitions of the terms that guides, labels and safety notices assume you already know — each linked to the guide that explains it.
In a real fire, get out first and call your local emergency number. This site is for learning and preparation — it never replaces emergency services.
Assembly point
A safe, agreed place outside a building where everyone gathers after evacuating, so people can be counted.
Backdraft
A sudden burst of fire when air reaches an oxygen-starved, superheated space. The supply of oxygen causes rapid re-ignition.
Breathing apparatus
The air-supply kit firefighters carry to let them operate in smoke-filled spaces they cannot otherwise breathe in.
CO₂ extinguisher
An extinguisher that uses carbon dioxide gas to smother a fire by displacing oxygen. Leaves no residue; rated for Class B and electrical hazards.
Combustion
The chemical reaction between a fuel and oxygen that produces heat and light — what we call burning. Requires heat to start and sustain it.
Compartmentation
Dividing a building with fire-resisting walls, floors and doors to slow the spread of fire and smoke, buying time to escape.
Conduction
Heat travelling through solid material — for example, a metal rod or wall. How heat can set fire to material on the other side of a barrier.
Convection
Heat moving through gases or liquids as a hot mass rises and cooler air replaces it. The main way hot smoke spreads through a building.
Defensible space
The cleared and managed area around a building that slows a wildfire and gives firefighters room to work.
Dry chemical extinguisher
An extinguisher that sprays a fine powder to interrupt the chemical chain reaction of a fire. Effective on Class A, B and C fires (US); leaves residue.
Ember
A glowing fragment of burning material carried by wind. Embers can travel far ahead of a wildfire front and start new fires.
Escape route
A planned and protected path from any point in a building to a final exit, kept clear at all times.
Fire blanket
A sheet of fire-resistant material used to smother a small fire — particularly useful for a burning pan or a person whose clothing is alight.
Fire door
A specially rated door designed to resist fire and smoke for a set time (e.g. 30 or 60 minutes), protecting escape routes and limiting spread.
Fire load
The total amount of burnable material in a space, expressed as the heat energy it would release if it all burned. Affects how intense a fire can become.
Fire tetrahedron
The four elements needed for sustained combustion: heat, fuel, oxygen and a chain reaction. Remove any one and the fire stops.
Fire warden
A trained person responsible for fire prevention checks, helping evacuations and reporting to the fire service on the day of an incident.
Flash point
The lowest temperature at which a liquid produces enough vapour to briefly ignite when a flame is applied. Below it, the liquid will not sustain burning.
Flashover
The near-simultaneous ignition of all exposed combustible surfaces in a room, triggered when heat reaches roughly 500–600 °C. A room is not survivable after flashover.
Heat alarm
A detector that responds to air temperature rather than smoke. Used where smoke alarms would give false alarms, such as kitchens.
Ignition temperature
The minimum temperature at which a material will self-ignite without a spark or flame. Varies by material.
PASS
The four-step method for using a portable fire extinguisher: Pull the pin, Aim at the base, Squeeze the handle, Sweep side to side.
Pyrolysis
The breakdown of a solid material by heat into combustible gases, before it actually bursts into flame. The gases then ignite.
Radiation
Heat travelling as invisible waves that warm objects across a room without touching them. How a fire can ignite material it is not in contact with.
Red flag warning
A US National Weather Service alert for conditions — low humidity, high wind, dry fuel — that significantly raise wildfire risk.
Smoke alarm
A device that sounds a loud alarm when it detects smoke, giving occupants time to escape. Should be on every level of a home.
Smoke layer
The hot layer of smoke that collects near the ceiling and descends as a fire grows. Crawling low keeps you below the worst smoke and heat.
Sprinkler
A ceiling-mounted device that releases water when its heat-sensitive element reaches a set temperature, controlling or extinguishing a fire automatically.
Stop, drop and roll
The emergency response if clothing catches fire: stop moving, drop to the ground, cover your face and roll to smother the flames.
Thermal imaging camera
A camera that shows heat instead of light, letting firefighters locate people and hot spots through smoke.
Wet chemical extinguisher
An extinguisher designed for cooking-oil fires (Class K/F). It creates a foam blanket that cools and seals the oil surface to prevent re-ignition.
Wildland-urban interface
The zone where houses and other buildings meet or mix with wild, grass or scrubland — the area at highest risk from wildfire.
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Similar words, different meanings
Pairs that sound alike but call for different understanding
Room ignites all at once when heat peaks.
Air rushes in when oxygen-starved fire suddenly gets supply.
Detects smoke; sounds earliest warning in most rooms.
Detects temperature. Better for kitchens; slower to trigger.
Energised electrical equipment — use CO₂ or dry chemical.
Flammable gases, such as LPG or propane.
Missing a word?
Seen a term on a label, notice or in a guide that isn't here? Tell us and we'll add a reviewed definition.
Glossary FAQ
Questions about fire safety terminology
Fire classification systems differ by country. The most common confusion is around Class C: in the US NFPA system, Class C means energised electrical equipment; in the European EN system, Class C means flammable gases. Each glossary entry flags which system it belongs to.
A smoke alarm detects airborne smoke particles and is recommended in living areas, bedrooms and hallways. A heat alarm responds to air temperature and is better suited to kitchens where cooking fumes would trigger false alarms from a smoke detector. Both are covered in NFPA 72 and UK Smoke and CO Alarm Regulations 2015.
Fire load is the total amount of combustible material in a space, expressed as the heat energy it would release if it all burned. A high fire load means a fire can grow very intense very quickly — relevant for warehouses, home offices and any room with large amounts of paper, wood or soft furnishings. NIST fire research uses fire load calculations to model building fire scenarios.
Yes. Use the "Missing a word?" section at the bottom of the glossary page or the contact form on the About page. We review suggestions monthly and add terms that appear in published fire-safety guidance from official bodies.