Example of Reversal of Flow – Backflow Backsiphonage Case 1

A rubber hose is submerged in a bedpan wash sink. — No backflow prevention device is installed on the bedpan washer or sterilizer.

A sterilizer connected to the domestic water system is allowed to cool without opening the air vent. As it cools, the pressure within the sealed sterilizer drops below atmospheric pressure producing a vacuum which draws the no-potable water from the bedpan wash sink into the sterilizer contaminating the contents. The water service line to the building is undersized and there is insufficient water for the building during high demands. A reversal of flow is created when there is a demand on floors below the floor where the sterilizer and bedpan washer are located. Since there is insufficient water to the building, when water in the building is being used on the bottom floors, the water in the piping system on the top floors is dewatered and a vacuum in the piping system is created.  As the water on the bottom floors is be used, a siphon effect is taking place within the top floor piping system pulling non-potable water into the domestic internal plumbing system creating a cross-connection incident and a public health threat.