Vent condenser: When should we go for a vent condenser?

I DO WORK IN A PHARMA INDUSTRY in technical services department...BULK DRUG MANUFACTURING UNIT..WE DEAL WITH SOMANY SOLVENTS LIKE n-hexane, methylene dicholride, petrochemical solvents...we do provide vent condensers for storage tanks of low volatile solvent...to prevent solvent losses due to vaporization//

but i would like to know when should we go for vent condenser...is there any criteria to go for vent condenser...based on volatility can we decide the requirement of vent condenser...plz discuss criteria for providing vent condenser for storage tanks...thanks in advance

I think it is based on economics and usage for the component.