Fugitive emissions are one of the most notable contributors to atmospheric releases in chemical process industries affecting not only the economy but also both the environment and workers’ health. In order to reduce fugitive emissions released in this process, the assessment of fugitive emissions should be conducted at the early stage of chemical process design when the cost of making changes is the lowest. This is however impeded by the limited knowledge on the leak sources, since the process is still under design. The paper presents a hybrid approach for estimating fugitive emission rates early in the design phase. The method combines a pre-calculated emission database of standard process module based approach with estimation by using generic piping and instrumentation diagrams if a suitable module is not available from the database. Also, both working and breathing emissions are included in the assessment. The emissions’ assessment from a case study of hydrodealkylation distillation and storage systems is presented to demonstrate the proposed approach.