Smokelayer user guide

Read this first: what the results mean

Every number in Smokelayer comes from a published empirical correlation or a simple zone balance. Each correlation was fitted to particular experiments and has a range; outside that range it can be badly wrong, and inside it the scatter of the original data is often tens of percent. The tool shows the assumptions, the stated range and the public source next to every result, and flags inputs or results that fall outside a stated range.

• Use the results to learn, to compare options and to sanity-check other work.
• Do not use them as the basis of a life-safety decision without review by a qualified professional: a fire protection engineer who knows the building and the rules that apply to it.
• Criteria such as pressure limits, door-force limits, tenability heights or detector ratings are your inputs. The tool contains no code tables and never declares a design acceptable.

Getting started

The workbench has seven tabs that share one study: Design fire, Plume, Ceiling jet & activation, Room & flashover, Smoke filling, Stair pressure and Report.

1. Open Examples and load a scenario, for example Office room, medium fire.
2. On Design fire, pick a growth class or a steady fire, set the peak heat release rate (HRR), the fuel area and the height of the fuel surface.
3. On Room & flashover, enter the room size, the vent and the lining. The ceiling height above the fuel used by the plume and detector tabs comes from here.
4. Move through the other tabs. Results update a moment after each edit; while they update, the previous numbers are dimmed.
5. Save writes a JSON study file; Open reads it back; CSV exports every result in the units you are viewing; Print prints the current tab.

Calculations run in a Web Worker on your device after a short domain check. Editing, saving and opening never need a calculation to finish. The study is autosaved in this browser only.

Units

The engine works in SI: metres, seconds, kilowatts, kelvin, pascals and newtons. The Units selector switches the display and the typed values between SI and US customary (feet, °F, Btu/s, cfm, in H₂O, lbf). Conversions use exact definitions (0.3048 m per foot, 4.4482216152605 N per lbf, 249.0889 Pa per inch of water). Lining properties are always entered in SI.

Changing units never changes the study: the stored values are SI and the same numbers come back when you switch back.

Design fire

A t-squared fire grows as Q = α (t − t₀)², where t₀ is an optional incubation delay. The growth classes are defined by the time t_g to reach 1055 kW (1000 Btu/s): slow 600 s, medium 300 s, fast 150 s and ultra-fast 75 s, so α = 1055 / t_g². The fire grows until the peak HRR, holds for the time you set, then decays linearly if you set a decay time.

A steady fire holds one HRR. A table fire is your list of (time, HRR) pairs, linearly interpolated; use it for a measured curve.

The convective fraction χc is the share of the HRR carried by the plume. A value near 0.7 is a common screening choice, but it depends on the fuel; it is your input.

Sources: growth classes and the 1055 kW definition as tabulated in NIST report NISTIR 5516 (Klote, 1994), section 2.2. The tool checks the class constants against that table's Btu column; its kW column prints two values (medium and ultra-fast) that do not match 1055/t_g², which the Verify page records.

Plume

Results on this tab use the peak HRR.

• Heskestad plume: virtual origin z₀ = 0.083 Q^(2/5) − 1.02 D, mean flame height L = 0.235 Q^(2/5) − 1.02 D, centre-line temperature rise and velocity above the flames, and plume mass flow. Below the flame height the mass flow is scaled linearly with height. For a fire against a wall or in a corner the entrainment uses the mirror method.
• McCaffrey centre-line correlations in three regions (continuous flame, intermittent, plume), from the total HRR.
• Simple plume mass flow, 0.071 Q_c^(1/3) z^(5/3) + 0.0018 Q_c, with its own flame height 0.166 Q_c^(2/5).

Limits: axisymmetric plume in still, uniform surroundings; temperatures inside the flame are not represented by the far-field plume equations (below the mean flame height Heskestad's centre-line values are not reported and McCaffrey's flame-region values are shown instead); the plume is unconfined, so above the ceiling height it is not physical.

Sources: NIST Technical Note 1889v1 (2015, technical reference of NIST's zone fire model), sections 3.3–3.4; NISTIR 5516 section 4; NBS report NBSIR 79-1910 (McCaffrey, 1979).

Ceiling jet and sprinkler or detector activation

The ceiling jet uses Alpert's steady correlations for temperature and velocity, with H the ceiling height above the fuel surface and r the radial distance of the sensing element from the plume axis. The element heats according to dT_d/dt = √u (T_g − T_d) / RTI. For a growing fire the jet follows the HRR at each moment (quasi-steady), and the equation is integrated exactly where the HRR is constant and with a fourth-order Runge–Kutta method, with steps no longer than a fifth of the element's response time, where it changes. Steps never cross a change in the design fire (a table point, the peak or the start of decay), so a short pulse is never missed and the result does not depend on the analysis duration. The steady closed form at the peak HRR and the smallest steady HRR that could ever operate the element are shown for comparison.

Enter the response time index (RTI) and the operating temperature from the product listing; the tool has no product tables.

Limits: smooth, flat, unconfined ceiling; fire away from walls; element at the hottest depth of the jet; no hot upper layer heating the jet; no conduction loss from the element; quasi-steady jet for a growing fire.

Sources: NRC Fire Dynamics Tools, NUREG-1805 Supplement 1 (2013), spreadsheet 10; NBS report NBSIR 85-3167 (Evans and Stroup, 1985); NIST TN 1889v1 section 6.1.

Room temperature and flashover

Choose the ventilation of the room:

• Natural (an open vent): the McCaffrey–Quintiere–Harkleroad (MQH) correlation gives the upper-layer temperature, and the Yamana–Tanaka formula gives the smoke layer height, held at the vent soffit once smoke can leave through the vent.
• Forced (mechanical ventilation): the Foote–Pagni–Alvares and Deal–Beyler correlations.
• Closed: Beyler's closed-compartment solution, which assumes a constant HRR. It is shown only when the HRR is constant over the whole analysis (a steady fire with no decay inside the analysis time); the Yamana–Tanaka height has the same condition.

The wall heat-loss coefficient comes from the lining: √(kρc / t) before the thermal penetration time t_p = (ρc/k)(δ/2)², and k/δ after it. When the design fire changes with time, the tool evaluates the correlations with the HRR at each moment; the original methods assume a constant HRR, so treat growing-fire curves as indicative.

Flashover HRR estimates by MQH, Babrauskas and Thomas use the vent and the enclosing area. They indicate the HRR at which flashover becomes likely; the design-fire time at which each value is reached is shown. An upper layer near 600 °C is flagged as a flashover indicator; beyond it the pre-flashover correlations do not apply.

Sources: NRC Fire Dynamics Tools, NUREG-1805 Supplement 1 (2013), spreadsheets 02.1, 02.2, 02.3 and 13; NIST TN 1889v3 section 2.1 for the comparison of flashover correlations.

Smoke filling and exhaust

Three views of smoke filling are shown together:

• The zone model is this tool's own two-layer mass and energy balance: the plume carries air from the lower layer into a uniform upper layer, a fraction of the convective heat can be lost to the boundaries, and an optional exhaust removes smoke from the layer. It accepts any design fire, and it stops (with a note) when the layer reaches the fuel surface, where the fire would burn inside the smoke, or 600 °C, where the two-layer picture no longer holds. In a forced-ventilation room only the exhaust entered on this tab enters the zone model.
• The filling correlations from NISTIR 5516 section 5 for a steady fire and for a t-squared fire. They estimate the first indication of smoke (conservative) and apply only to spaces of constant plan area with A/H² between 0.9 and 14 (steady) or 1 and 23 (t-squared), and z/H between 0.2 and 1.0; outside these ranges the tool flags the result.
• Yamana–Tanaka from the Room tab, for a naturally vented room with a constant HRR.

Where a correlation leaves its stated range the curve is cut off (never extrapolated) and an Outside range note says where. The steady correlation needs an HRR that is constant over the analysis; the t-squared correlation is drawn only until the fire reaches its peak. In the zone model, when the exhaust removes more volume than the plume brings, no layer forms (or an existing layer is drawn down until it is gone).

The steady exhaust box gives the smoke exhaust that holds a chosen clear height above the fuel under a steady fire: the exhaust mass flow equals the simple-plume flow at that height, with an adiabatic layer. It does not check plugholing, make-up air or the layer depth needed at the exhaust inlets.

Sources: NISTIR 5516 (Klote, 1994) sections 5.1–5.3; zone model verified on the Verify page against an independent quadrature.

Stair pressurisation

The Stair pressure tab covers basic stair pressurisation with all stair doors closed:

• the stack-effect pressure gradient b = K_s (1/T_o − 1/T_B), with K_s = g p / R;
• the stair-to-building pressure difference along the height, with the minimum set to your minimum criterion;
• the height limit above which a simple system cannot keep the pressure inside your min–max band;
• the supply air for the stair (with your safety factor);
• the door-opening force from the hinge moment balance F = F_r + W A ΔP / (2 (W − d)), and the pressure difference at which your force limit is reached.

Limits: no vertical leakage in the building, uniform leakage on every floor, no wind, all stair doors closed. Opening stair doors drops the pressure sharply; systems that compensate for open doors need a network analysis that this tool does not perform.

Sources: NIST report NISTIR 4551, Design Manual for Smoke Control Systems (Klote, 1991), chapters 3, 4 and 7.

How we verify Smokelayer

The Verify page runs the same case list that the automated tests run. Validation cases reproduce published worked numbers from public US-government reports: the NRC Fire Dynamics Tools spreadsheets and their printed examples, NIST reports NISTIR 5516 and NISTIR 4551, and NBS reports. Verification cases compare the engine with independent derivations: closed forms, conservation laws, numerical quadrature and a separate integrator, including a step-size study of the detector integrator. Each case shows its inputs, its source, its tolerance and why that tolerance is appropriate. A case whose source could not be opened is shown as pending source with no numbers.

Passing these checks means the arithmetic reproduces the published methods. It does not mean a correlation is right for your building.

Files, privacy and limitations

Studies are JSON files with a format name and version; files from a newer version are refused with a message rather than misread. CSV exports start with a profile line, carry the study title, the unit system and the export time in Mountain Time, and neutralise text that a spreadsheet could treat as a formula.

Your inputs stay in your browser. The analysis horizon is at most 10 hours, an HRR table holds up to 400 rows, and a study file is at most 1 MiB.