In a fertilizer manufacturing plant, during his inspection round, an operator detected a hydrogen leak at a flange of an exchanger located between the conversion and decarbonisation stages of the ammonia processing unit. He alerted the control room. A steam hose is installed blowing towards the flange to dilute the leak. Explosive gas measurements are taken twice per shift to ensure that the consequences of the leak are under control. The area is placed under surveillance. A few days later, 2 vapour rings were placed around the flange. A marker was also placed around the flange to indicate that access to the area was prohibited. Several control points are defined. Three weeks later, a leak sealing system under is put in place. Two weeks later, the injection of sealing paste into the collar does not seal the leak. Two months after detection of the initial leak, an operator notices short term changes in noise and direction at the leak. The operator finally decides to work on the leaking flange. The main process gas supply is shut down more than 9 weeks after the initial leak detection while maintaining a nitrogen flow. The gas flow stops in the pipe.