The inherent safety level (ISL) assessment of a heat exchanger network plays a vital role in developing its inherently safer design. New essential safety indices, i.e., inherent safety index for shell and tube heat exchanger (ISISTHE) and overall safety index for heat exchanger network (OSIHEN), are introduced to overcome this potential gap. A prototype tool is proposed by integrating these indices to a process design simulator via object linking and embedded automation. The heat exchanger network of an ammonia synthesis process and a steam reforming unit are presented as a case study. In conclusion, this prototype tool was found to have the potential to figure out a dangerous heat exchanger in a network.