Sodium hypochlorite poses explosive hazards associated with its complex reactive chemistry. The production process of sodium hypochlorite consists of a first block where the chlorine, caustic soda and hydrogen are produced in an electrolytic cell from brine and a second block where chlorination of caustic soda to form hypochlorite is carried out. This process is characterized by several hazards such as chlorine gas toxicity, explosive hazards due to the presence of hydrogen and chlorine and corrosive hazards. Loss of control of such substances has the potential to cause high-consequence low-probability events. Thus, specific safety measures have to be designed to mitigate risk. In the present work, the risk assessment of the first block of the process is performed, focusing on hydrogen risks. To this end, HAZOP analysis was performed to identify the top events. For each top event, based on properly developed fault trees, the frequency analysis was performed. Eventually, the consequence analysis was carried out by the simulation of phenomena leading to dispersion and consequent ignition of the cloud as function of the distance from the source. Simulations were performed by means of the software PHAST
