Coffee Break Training: Automatic Sprinklers: Cross-Connection Control in Existing Buildings [open pdf - 128KB]
"In recent years, some water purveyors have pursued aggressive retrofit programs requiring the installation of backflow prevention devices on existing fire protection systems. Their goal is to decrease the chances that the often dirty, static water that accumulates in a fire protection system will flow backward and contaminate a potable water supply. This effort is called 'cross-connection control.' While there has been considerable debate between fire protection and water company professionals regarding the likelihood of cross-connection contamination, one thing is clear: The selection and installation of backflow prevention devices on existing sprinkler systems must be done carefully to ensure reliable fire protection system operation. Some existing fire protection systems, especially hydraulically engineered sprinkler systems, may have been designed with very precise or no safety margins in their operating pressures. This means that any deterioration of the incoming water pressure may have a deleterious effect on the sprinkler discharge pressure and water distribution pattern. By requiring the installation of some sort of backflow prevention device in an existing system that may have a narrow safety margin, the friction loss characteristics of the backflow prevention device may significantly affect fire protection system performance. Of course, the influence of the cross-connection control device must be evaluated on any new fire protection system. For example, in the backflow prevention device illustrated here, its laboratory-controlled flow test reports indicate that it may reduce water pressure from 2 to 14 pounds per square inch (0.14 to 0.96 bar) between the inlet and outlet pressures."
Coffee Break Training - Fire Protection Series No. FP-2014-45
U.S. Fire Administration: http://www.usfa.fema.gov/