This model is based on the same outputs as the two-box model, namely Near Field and Far Field concentrations. In the modified two-compartment model, the Near Field volume is redefined on the basis of certain specific exposure determinants described in the list below. The purpose of including these different parameters in the model, such as source directivity, emission velocity or degree of turbulence, is to ascertain whether the Near Field or Far Field concentration should be used in a given exposure scenario.

VME (Valeur Moyenne d’Exposition) Reference exposure concentration [mg/m3]
G total mean emission over the working period in question
V workplace volume (m3)

Q general workplace air supply: this parameter can either be expressed as air flow (m3/min) or air exchanges per hour.

d distance from source to operator

T turbulence close to the source: express this parameter qualitatively:

• weak
• standard
• strong

D directivity

• omni-directional
• directed away from the measuring point
• directed towards the measuring point

v source velocity

• low
• moderate
• high

Model output:  

The results are expressed as %VME. The graph generates the two levels (Far and Near Field) calculated by the classic model and, depending on the result of the modified model, indicates which level should be associated with a given exposure scenario.