One phase of the Joint District, Federal and State Project for the Evaluation of Refinery Emissions was the study of hydrocarbon leakage from pressure relief valves. The report details the techniques and conclusions of the study. The seven major refineries in the Los Angeles area, processing about 90 per cent of the local crude throughput, reported a total of 1100 relief valves on operational units and 350 relief valves on pressure storage vessels. Field tests made on 460 valves indicated an average leak for valves on operational units of 2.9 pounds per day per valve while pressure storage valves leaked an average of 0.4 pounds per day per valve. The total hydrocarbon leakage, calculated by projecting the field test data to the reported number of valves in each group, was found to be 3500 pounds per day. This figure includes only continual leakage through the valve seat. Emissions due to relief valve blowoff were not considered in the study. (Author)