Flammable Vapor Storage Ventilation Simulator

Storage Room Conditions

Drum leak / evaporation severity 18 g/min

Ambient temperature 22 °C

Extraction ventilation 6 ACH

Vapor Concentration

— SAFE —

0%100% LELUEL>UEL

Concentration

0 ppm

% of LEL

Ventilation flow

0 m³/min

Steady-state %LEL

How it works

The storage room is modelled as a single well-mixed volume V (150 m³) with a solvent vapor source (evaporation rate G) and a mechanical exhaust flow Q. Vapor mass balance:

dC/dt = G/V − (Q/V)·C
Q = ACH · V / 60          (m³/min, from air changes per hour)
G(T) = G₀ · exp(k·(T−20°C))   (evaporation rises with vapor pressure)
ppm = C[mg/m³] · 24.45 / M     (M = 92.1 g/mol, toluene-like solvent)
%LEL = ppm / LEL_ppm × 100     (LEL = 11,000 ppm, UEL = 71,000 ppm)

At equilibrium dC/dt = 0, so the steady-state concentration is simply C_ss = G/Q — more ventilation or less leak both scale it down linearly, which is why fire codes size storage-room exhaust as air changes per hour rather than a fixed fan.

Below 25% LEL — safe margin under NFPA/OSHA housekeeping limits.
25%–100% LEL — caution zone; ventilate before any hot work.
100%–UEL — inside the flammable range: a spark or hot surface here can ignite the cloud.
Above UEL — too fuel-rich to ignite (not enough oxygen), but still toxic and will pass back through the flammable range as it dilutes.

The ignition test samples the current %LEL against these same thresholds — it only "catches" while the mixture sits inside the LEL–UEL window, exactly like a real vapor cloud.

Drum / leak source Extraction vent Vapor cloud (color = %LEL)

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