Local Exhaust Ventilation & Irritant Concentration Simulator

Source & Ventilation

Emission rate G 120 mg/min

General ventilation 4.0 ACH

Local exhaust hood flow Q_lev 600 m³/h

Source→hood distance x 0.60 m

Room Air Quality

0% of OELOEL = 5.0 mg/m³

Concentration C(t)

0.00 mg/m³

Steady-state C_ss

0.00 mg/m³

Hood capture velocity

0.0 m/s

Capture efficiency η

How it works

The room is modelled as a single well-mixed control volume (a standard industrial-hygiene mass-balance model). Contaminant mass enters at generation rate G and leaves through general dilution ventilation and the local exhaust hood:

dC/dt = (1 - η)·G / V  -  (Q_gen + Q_lev)·C / V

Q_gen = ACH · V / 3600        [m³/s from air changes/hour]
C_ss  = (1 - η)·G / (Q_gen + Q_lev)   [steady state]
C(t)  = C_ss + (C0 - C_ss)·exp(-k·t),  k = (Q_gen+Q_lev)/V

The hood's local capture is governed by the classic unflanged circular-opening capture-velocity equation (ACGIH Industrial Ventilation manual):

v_x = Q_lev / (10·x² + A)

x = distance from source to hood face, A = hood face area
η = min(0.95, 0.95 · v_x / v_required)

Capture velocity falls off with the square of distance — moving the source a little further from the hood costs far more than the flow-rate slider alone suggests. When v_x reaches the required control velocity (0.5 m/s, typical for irritant vapors/gases), the hood captures up to 95% of the emission before it ever mixes into the room; the rest is left to the slower general-ventilation term. The floating gas particles are colored by local concentration and drift along the combined capture + mixing flow field; they are a visualization of the same C(t) driving the numeric readouts, not an independent simulation.

Emission rate — how fast the irritant is generated at the source (a leak, an open solvent tank, a spray booth).
General ventilation (ACH) — whole-room dilution airflow, expressed as air changes per hour.
Hood flow Q_lev — local exhaust volumetric flow captured right at the source.
Distance — source-to-hood distance; pull the slider up and watch capture efficiency collapse even at constant Q_lev.

Clean air (<25% OEL) Elevated (25–100% OEL) Over OEL

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