Soot Horizon
Definition
The visible line on vertical surfaces marking the lowest height reached by the smoke layer during the early fire growth phase, representing the hot gas layer boundary before the layer became too hot for soot deposition.
- Appearance
- Visible line on vertical surfaces marking lowest smoke layer reach
- Phase
- Forms during early fire growth
- Represents
- Hot gas layer boundary before it became too hot for soot deposition
- Field
- Compartment fire behaviour and plume interpretation
Common questions
How do investigators use a soot horizon to reconstruct fire development?+
By mapping the height of soot horizons across multiple walls and rooms, investigators can infer how the hot gas layer descended over time and where it originated, helping reconstruct the sequence and direction of early fire growth rather than only the final damage pattern.
Why does soot deposition stop once the gas layer gets hot enough?+
At higher temperatures soot particles are more fully combusted or carried further before they can adhere to a cooler surface, so the horizon marks conditions during the earlier, cooler growth phase rather than the peak temperatures reached later in the fire.
Related terms
- Alpert Correlation
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- CFAST
- Consolidated Fire and Smoke Transport model from NIST; a multi-room two-zone fire model used for evacuation time analysis, detector performance prediction, and...
- Fractional Effective Dose (FED)
- A physiological model that combines exposure to CO, HCN, CO2, reduced O2, and heat into a cumulative incapacitation estimate. Used with FDS...
- Heskestad Correlation
- An analytical expression derived by Gunnar Heskestad at FM Global relating fire plume centreline temperature to heat release rate and height above...
- McCaffrey Plume Model
- A three-zone empirical model for fire plume centreline temperature and velocity developed by Brian McCaffrey at NIST, with separate power-law relationships for...
- NIST FDS (Fire Dynamics Simulator)
- A freely available large-eddy simulation CFD code from NIST that models coupled fire, smoke, and heat transfer in three-dimensional geometries. Validated against...
- T-Squared Fire Growth
- A model in which heat release rate increases as the square of time from established burning (HRR = alpha × t²). The...
- Two-Zone Model
- A compartment fire model that divides the room into an upper hot gas zone and a lower cool ambient zone, computing their...
- Virtual Origin
- In plume correlation models, the effective point source location below the actual fuel surface from which the plume behaves as if it...