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Saturation Concentration β
Saturation Concentration
The calculated saturation concentration (the theoretical maximal concentration) in mg/m3 at the given temperature of the vapour pressure is presented. This concentration does not take into account any spraying effects or movement at the liquid boundery layer and the like. The following formula is used to calculate the theoretical saturation concentration:
Csat = 16036*M*PT/T [mg/m3]
Of which:
- M = the Molecular Mass of the substance;
- T = the temperature in degrees Kelvin
- PT = the Vapour Pressure in mm Hg;
This formula is an elaboration of:
Csat = M/22,4*273/T*PT/760*10^6 [mg/m3]
- M/22,4 = the conversion factor from ppm to mg/m3 at 273 K (0οΏ½C);
- PT/760 = the relative Vapour Pressure. This is for an ideal gass equal to the Molar Ratio of the substance in the surrounding air and therefore equal to the concentration in ppm of vol %.
Illustration
The maximal Vapour Pressure used for the calculations of concentration in air can never be higher than the existing air pressure (1 atmosphere, 101,3 kPa, or 760 mm Hg). The Vapour Pressures that are indicated in the literature (and are also presented in DOHSBas) for gasses and very volatile substances present what the Vapour Pressure can be, when the substance would have a Boiling Point of 25οΏ½C. This can be calculated with the Antoine Equation. In such a situation DOHSBase Compare does not present the Theoretical calculated (very high) value, but rather the saturation concentration as > 1.000.000 mg/m3.
The ratio between Saturation Concentration and the Occupational Exposure Limit is a measure for the Exposure Potential of a substance. The higher the ratio the higher the risk that a Concentration Treshold Value will be exceeded when an emission takes place. The ratio is for most gasses and liquids with a low Boiling Point (< 350οΏ½C) higher than 1.
For solid substances and liquids with a high Boiling Point and a low Vapour Pressure the concentration at the workplace can still be higher than a Threshold Value when these substances are sprayed. As an example, Phosphoric Acid has a Vapour Pressure of P = 2*10E-11 mmHg and a Boiling Point of 213οΏ½C. The saturation Vapour Concentration is at ambient temperature (298 degrees K) around 0,001 mg/m3. The Occupational Exposure Level (vapour + aerosol) is 1 mg/m3 (TWA 8 hours) and can easily be reached when an acid fog mist is formed.