AFFF foam-type concentrate

The foam concentrate used with subsurface systems should be a fluoroprotein type for best results, although some AFFF foams are listed for substitutable application (because of their "fuel shedding" properties). The minimum foam solution rate should be 0.3 gpm/ft (12 Ipm/m ). The supply of foam liquid should be adequate to operate the system for 20 minutes. The foam injection point must be above the level of any residual water in the bottom of the tank. Subsurface foam application is not recommended for open or covered floating roof tanks or cone roof tanks with internal floating covers. 

Fluoroprotein and alcohol resistant type AFFF concentrates are suitable for seal protection of open top floating roof tanks. Foam may be applied from fixed chambers in an "over-the-top" fashion or by discharge from "foam chambers" located at the top of the tank shell allowing the foam to run down the inside wall of the tank shell onto the seal area. Subsurface foam on floating tanks is generally not recommended as a sunken roof would block the foam distribution. Typical protection is shown in Table 7-10. 

---