Generation rate · Dilution ventilation · LEV hood design
How to Use
Enter how much liquid substance is consumed or evaporated during the process, and over what duration. The calculator estimates the airborne generation rate assuming all evaporated liquid becomes airborne vapour. Use the result in Tool 2: Dilution Ventilation.
Substance
Optional — enables volumetric vapour rate output
Consumption
Enter 100% if all liquid evaporates (open surface, spray). Reduce for dip tanks or processes where liquid is partly retained.
Results
Generation Rate G
—
mg/s
Generation Rate G
—
mg/min
Generation Rate G
—
g/hr
Volumetric Vapour Rate (20°C)
—
ppm·m³/s
Interpretation
Generation rate is calculated as: G = (Amount × SG × fraction) / Duration. This assumes all evaporated liquid becomes vapour at ambient conditions. Actual airborne concentration depends on the room’s ventilation — enter this value in Tool 2: Dilution Ventilation to calculate the required flow rate.
Mass converted to mg; SG used to convert volume to mass for liquid inputs. Duration converted to seconds. Volumetric vapour rate uses Vm = 0.02404 m³/mol at 20°C.
How to Use
Enter the contaminant generation rate, your target concentration (typically the OEL), and the room mixing factor. Press Calculate to find the required ventilation flow rate and air change rate.
Contaminant Source
Required if concentration entered in ppm
°C
Target Concentration
Enter molecular weight above to enable ppm input.
Room Conditions
m³
Optional — required for ACH calculation
Mixing Factor
Results
Required Flow Rate
—
m³/s
Flow Rate
—
m³/min
Flow Rate
—
L/s
Flow Rate
—
CFM
ACH
—
air changes/hr (at required Q)
Time to 90% of C target
—
from clean room start
Time to 99% of C target
—
from clean room start
Interpretation
Dilution ventilation is suitable for low-toxicity vapours with OELs above approximately 50 ppm. It is generally not appropriate for highly toxic substances, carcinogens, or sensitisers regardless of concentration.
Concentration vs. Ventilation Rate
Formula: Q = G × k / C (ACGIH dilution ventilation equation). Molar volume corrected for temperature.
ACH = Q × 3600 / V. Results assume steady-state conditions and uniform mixing (corrected by factor k).
How to Use
Select a hood type, enter the required capture velocity and capture distance. The calculator applies the appropriate ACGIH hood equation to determine the required airflow. Use the minimum duct transport velocity table to ensure adequate conveying velocity in the connected ductwork.
Process & Capture Velocity
m/s
Typical range: 0.25–10 m/s. See ACGIH ‘Industrial Ventilation’ Table 3-1.
Hood Type & Geometry
m
m
m
m
Ductwork
Results
Required Airflow Q
—
m³/s
Required Airflow Q
—
m³/min
Required Airflow Q
—
CFM
Face Velocity
—
m/s at hood opening
Min. Transport Velocity
—
m/s (duct conveying)
Recommended Duct Size
—
mm diameter
Required Airflow vs. Capture Distance
Interpretation
The recommended duct diameter is based on minimum transport velocity only. A full duct system design must account for branch balancing, pressure losses, and fan selection — consult a ventilation engineer for complex systems.
ACGIH hood equations applied as specified in ‘Industrial Ventilation: A Manual of Recommended Practice for Design’ (ACGIH). Duct sizing based on minimum transport velocities from ACGIH Table 5-2. All results are engineering estimates; site-specific conditions may require adjustment.