If a person is exposed to a mixture of chemicals, then the threshold limit value (TLV) for the mixture can be estimated by adding together the ratio for the concentration to the TLV for each chemical.
Threshold Limit Value for a chemical mixture of N compounds =
= sum of ratios for the concentration of each chemical to its TLV=
= ((concentration of chemical #1) / (TLV for chemical #1)) + ((concentration of chemical #2) / (TLV for chemical #2)) + ..... + ((concentration of chemical #N) / (TLV for chemical #N))
Interpretation:
• If the sum of the ratios <= 1, then the threshold is not exceeded.
• If the sum of the ratios > 1, then the threshold is exceeded.
Converting Units
Data on TLV is expressed as parts per million (ppm) or milligrams per cubic meter of air (mg/m^3).
TLV in mg/m^3 =
= (TLV in ppm) * (gram molecular weight of substance) / (24.5)
TLV in ppm =
= (TLV in mg/m^3) * (24.5) / (gram molecular weight of substance)
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