Black water is present in fire systems 3. Siamese fittings add potential hazard 4. Auxiliary water supplies may not be potable 5. Toxic anti-freeze additives can be present 6. Excess pressure pumps boost house pressure 7.
Pressure drops in the potable supply set up backsiphonage potential.
The alarm check is not a true backflow preventer Figure 2 . The alarm check contains a lightly-loaded, soft seated, single check valve assembly. It is not designed, manufactured, or marketed to be a testable backflow preventer installed for the express purpose of protecting the potable water supply. The single check can leak due to debris fouling, and pass stagnant fire line water from the house side of the alarm check, back into the street side. Magnified View of Black Water Water sitting in typical standard black iron pipe, which is used for most standard fire protection system installations, sits in an anaerobic environment, is stagnant, can contain bacteria, and is a very unpleasant substance.