Ten kilos (22 pounds) of hydrogen chloride gas was released from a flange that had been fitted by a contractor just a few weeks earlier, triggering alarms and resulting in an internal emergency intervention. The incident had no significant consequences. A contractor performing maintenance was instructed to remove the pressure sensor from a device and replace it with a blind flange. Due to the corrosive environment (HCl), the plate on the pressure sensor was coated with tantalum. After being removed, the pressure sensor was supposed to be closed off with a Teflon®-coated full flange. As none were in stock in the site’s workshop, the contractor was given a standard flange and a Teflon® sealing disc. This type of substitution is routine.