Appearance
Threshold exceedance Index (TIX) β
Threshold exceedance Index (TIX)
The Threshold exceedance IndeX (TIX) describes in fact the 'ability to become airborne' and is calculated using the following formula:
TIX=10log(Csat/OELV)*4/7
in which:
Csat = the theoretically calculated saturation concentration of the substance in air.
OELV = the numerical value of the Occupational Exposure Limit Value, used in the selected type of OELV.
The formula has no scientific basis. Because the values of TOX varie between 0 and 4 or 5 it was decided the TIX value also vary between 0 and 4. The value 0 is not included in the calculation of the Risk Assessment Score (RAS).
If: Csat/OEL<1, then TIX is 0.
After all, if the saturation vapour concentration (Csat) is less than the OELV, then the substance in vapour form can't exceed the OELV.
Calculated from observations of the ratios Csat/OELV, showed that most of the ratios Csat/OELV are less than 1E+7.
To limit TIX to an upwards to 4, 10log(Csat/OELV) is multiplied by 4/7, and all values for 10log(Csat/OELV)*4/7 > 4 are set to be equal to 4.