Compartment Fires as the Context for Smoke Control
Most building fires do not start in open atriums or tunnels. They start inside rooms, corridors, shops, or apartments with walls, doors, and ceilings that form a fire compartment. The way a fire grows inside that closed volume decides how smoke layers form, how long escape routes stay tenable, and what demands fall on the smoke control system.
For ventilation and smoke engineers, understanding compartment fire behavior gives the background for sizing smoke exhaust, locating dampers, and planning pressurization strategies that support the structural fire concept.
What Makes a Compartment Fire Different
A compartment fire develops inside a defined envelope. That envelope shapes both the flames and the smoke.
Key elements include:
- Boundaries – Walls, floors, and ceilings with specified fire-resistance ratings
- Openings – Doors, windows, leakage gaps, and duct penetrations that let air and smoke move
- Fuel load – Furniture, stock, finishes, and plastics that determine how much energy the fire releases
- Ventilation conditions – How much oxygen reaches the fire and where hot gases can escape
Because the volume and leakage of a compartment are limited, the fire’s growth and smoke production depend strongly on how the space connects to adjacent rooms and shafts.
Typical Development of a Compartment Fire
Fire engineers often describe a compartment fire as moving through several characteristic phases. The exact timelines vary, but the pattern helps explain smoke behavior and tenability.
Early growth
- A local ignition source (electrical fault, open flame, hot surface) ignites nearby fuel.
- Flames remain near the origin, but hot gases start to collect under the ceiling.
- A distinct smoke layer forms and thickens; visibility in the upper zone drops first.
In this phase, people often still have time to escape if detection and alarm systems work promptly.
Flashover and fully developed burning
If the fire continues to grow and enough air enters the compartment, temperatures near the ceiling rise sharply. Radiant heat from the hot layer and flames heats other items until many surfaces ignite in quick succession. This transition is flashover.
After flashover:
- The entire compartment can burn, with very high temperatures.
- The smoke layer becomes deep and extremely hot.
- The fire now depends more on available ventilation than on local fuel near the origin.
At this point, unprotected structural elements, services, and contents face severe thermal loading.
Decay
As fuel or oxygen become limited, the fire starts to decay:
- Heat release rate decreases.
- Temperatures fall, but the compartment can still hold toxic gases and low oxygen.
- New ventilation openings (for example, broken glass or opened doors) can cause changes in behavior, including secondary flaming.
Fire and rescue tactics, plus smoke control actions, need to consider that a decaying fire can still be dangerous if fresh air arrives suddenly.
Compartmentation, Smoke, and Ventilation Interaction
Compartmentation aims to keep fire and smoke in one place long enough for people to escape and for responders to work. Ventilation can either support or undermine that goal.
Important interactions include:
- Doors and leakage – Open doors, gaps, and failed seals let smoke move into adjacent compartments and shafts.
- Ductwork and dampers – Poorly protected ducts can move smoke between compartments; correctly placed fire and smoke dampers limit that spread.
- Ceiling voids and shafts – Hidden spaces above ceilings or inside shafts can become unplanned smoke paths if not detailed and separated correctly.
Smoke-control design needs a clear view of these paths so fans and dampers help the compartmentation strategy instead of fighting it.
What Compartment Fires Mean for Smoke Control Design
Clear design objectives
Engineers cannot design effective smoke systems without defining what they want to achieve during a compartment fire, such as:
- Keep escape routes and stairwells tenable for a defined period.
- Limit smoke spread beyond the fire compartment.
- Support firefighter entry and operations in specific zones.
Once these targets are set, smoke exhaust, pressurization, and make-up air can be sized and sequenced to match realistic compartment fire scenarios.
Matching fan behavior to fire development
Fans that help comfort cooling may not behave correctly during a fire if designers do not consider compartment behavior. Good fire-mode logic:
- Stops nonessential fans that might spread smoke.
- Starts smoke exhaust fans and pressurization fans with defined priorities.
- Coordinates damper positions so the system controls flow paths rather than leaving them to chance.
The compartment fire model gives the background for choosing design fire sizes, smoke production rates, and temperatures for this fire-mode analysis.
Respecting structural and fire-resistance limits
Compartment boundaries exist to protect structure and adjacent spaces for a defined time. Smoke control design needs to:
- Avoid overpressurizing compartments or shafts in ways that damage fire barriers.
- Keep high-temperature smoke within components rated for that exposure.
- Align smoke exhaust points with the overall fire strategy, not only with duct-routing convenience.
This coordination keeps FIRE SAFETY performance coherent across architecture, structure, and mechanical systems.
FAQ
What is a compartment fire?
A compartment fire is a fire that develops inside a room or enclosed space bounded by walls, a floor, and a ceiling. The enclosure limits where heat and smoke can go, so the fire’s growth and smoke layer depend strongly on the compartment’s size, fuel load, and ventilation openings.
What is a fire compartment?
A fire compartment is a part of a building surrounded by fire-resisting construction, such as rated walls, floors, and doors. Its purpose is to contain fire and smoke for a specified time so people can escape and so the fire does not spread freely through the entire building.
What is the meaning of contained fire?
A contained fire remains within a defined area and does not spread beyond its boundaries. In buildings, that usually means the fire stays inside one room or compartment, with fire doors, barriers, and construction preventing flames and smoke from moving into adjacent spaces for a period.
What is an example of fire compartmentation?
A typical example is a hotel where each guest room, corridor, and stair core forms a separate fire compartment. Rated walls and doors between these areas slow fire and smoke spread, while ventilation and smoke control systems respect those boundaries in their design and operation.
What are the stages of a compartment fire?
A compartment fire usually passes through ignition, growth, possible flashover, a fully developed phase, and decay. During growth, smoke layers form and temperatures rise; flashover marks a rapid transition to severe conditions; decay follows when available fuel or oxygen no longer supports high heat release.
What is an example of compartmentation?
Beyond fire, compartmentation appears wherever designers divide a system into separated zones. In building fire safety, that means splitting floors into compartments with rated walls and doors. In ships, watertight bulkheads create compartments that limit flooding, which follows the same containment principle.
What is the 30/30/30 rule for fire?
Different organizations use “30/30/30” in various ways, but in many building contexts it informally refers to compartments or elements designed to provide at least 30 minutes of fire resistance for integrity, insulation, and stability. Exact rules and ratings come from local codes, so engineers always refer to the applicable standard when they set compartment performance.
What counts as a contained fire?
A fire counts as contained when it stays within its intended compartment or enclosure and does not compromise the structure or escape routes beyond that zone during the required period. Walls, doors, ceilings, and coordinated smoke control measures work together to maintain that containment.
About YAOAN VENTILATION
YAOAN VENTILATION delivers optimized air and airflow management solutions backed by nearly three decades of engineering experience. Since 1996, we have focused on industrial-grade ventilation and fire protection systems for commercial buildings, infrastructure, and specialized environments. Our portfolio includes fans, fire and smoke dampers, smoke-control components, silencers, and precision-built aluminum ventilation parts that integrate with compartmentation and fire strategies. By designing smoke control around realistic compartment fire behavior, YAOAN VENTILATION helps projects protect escape routes, support firefighting operations, and maintain consistent, code-compliant performance over the full life of the building.