[en] Derived Air Concentration (DAC)values for tritium being high ie., 8x10⁵Bq/m³(∼ 21.6 μCi/m³) the ambient moisture samples corresponding to such levels normally contain relatively high concentration in aqueous form. This provides comparatively larger currents in a single PMT/LS system even though the background due to thermionic noise is not very small. In nuclear power stations during operations and maintenance fraction of DAC or even higher orders of DAC of tritium are encountered. Additionally periodic inventory of moderator and coolant of PHWR systems are carried out wherein samples containing relatively larger concentration of tritium need to be analysed. Utilising these factors a simple single PMT/LS system has been designed for such purposes. The PMT used was EMI 9635 which has a dark current 10^-10 amps. A cocktail containing 10 ml of dioxan (or even smaller volumes) was used for tritium in aqueous form. A digital readout is also provided for convenience. Air concentration of tritium corresponding to several values and fractions of DAC are monitored and found that lowest detection limit was 0.05 DAC. The results obtained were compared with LSS coincidence system (Packard 4530) and correlation among the results was found to be satisfactory. The paper summarises the advantages and disadvantages of the method described. (author). 3 figs