Ventilation Dilution Calculator

Calculate required dilution ventilation to control airborne contaminants below TLV/PEL limits.

Generation Rate (mg/min)

Molecular Weight (g/mol)

TLV/PEL Limit (ppm)

Safety/Mixing Factor (K)

Supply Air Conc. (ppm)

Room Volume (ft³)

Tab to move between fields

Required Ventilation (CFM)

55.3

Dilution Ratio500,000

Air Changes / Hour Needed0.66

Vapor Generation (CFM)0

Target Concentration (ppm)10

Steady State No Dilution110.7

Steady State At Required10

How to Use This Calculator

Enter Generation Rate (mg/min), Molecular Weight (g/mol), and TLV/PEL Limit (ppm).
Set Safety/Mixing Factor (K), Supply Air Conc. (ppm), and Room Volume (ft³).
Review the Required Ventilation (CFM) result.
Use Dilution Ratio and Air Changes / Hour Needed to inform your decision.

How the result changes with Molecular Weight (g/mol)

Generation Rate (mg/min): Contaminant generation rate in milligrams per minute from evaporation or off-gassing.
Molecular Weight (g/mol): Molecular weight of the contaminant. Examples: benzene=78, toluene=92, acetone=58, xylene=106.
TLV/PEL Limit (ppm): Allowable exposure limit: TLV (ACGIH) or PEL (OSHA) in parts per million.
Safety/Mixing Factor (K): Mixing inefficiency factor. K=3 for good mixing, K=5 average, K=10 poor mixing or high toxicity.
Supply Air Conc. (ppm): Background contaminant concentration in the supply (makeup) air. Usually 0 for clean outdoor air.
Room Volume (ft³): Total room volume for computing required air changes per hour.

Required Ventilation (CFM): Volume of dilution air needed to keep contaminant below the exposure limit.
Dilution Ratio: Ratio of clean air volume to contaminant vapor volume.
Air Changes / Hour Needed: Required ACH for the given room volume. >60 ACH suggests local exhaust is more practical.
Vapor Generation (CFM): Contaminant vapor generation rate converted to volumetric flow at STP.
Target Concentration (ppm): Steady-state concentration at the required ventilation rate (equals the TLV/PEL).

Identify Input Parameters
4 parameters
Generation Rate (mg/min) = 10, Molecular Weight (g/mol) = 78, TLV/PEL Limit (ppm) = 10, Safety/Mixing Factor (K) = 5 = 6 input(s) provided
Calculate Required Ventilation
Required Ventilation = effectiveLimit > 0
55.3 = 55.3
Calculate Dilution Ratio
500000 = 500000
Calculate Air Changes / Hour Needed
0.66 = 0.66