NFPA 11, NFPA 11, Standard for Low-, Medium-, and High-Expansion Foam, covers the design, installation, operation, testing, and maintenance of low-, medium-, and high-expansion and compressed air foam systems for fire protection. It is used by those responsible for designing, installing, testing, inspecting, approving, listing, operating, or maintaining fixed, semifixed, or portable foam fire-extinguishing systems. These are used to protect interior or exterior hazards such as tanks, loading docks and storage of flammable liquids. This standard describes how these systems should be designed, installed and maintained; other NFPA codes, such as NFPA 30 Flammable and Combustible Liquids Code and NFPA 409 Standard on Aircraft Hangars, specify where and to what degree foam protection is required. Low-, medium-, and high-expansion foam systems are intended to provide property protection, not life safety.
When a system is initially installed, an acceptance test must be performed by qualified personnel to meet the approval of the Authority Having Jurisdiction (AHJ) and ensure proper functionality. An important aspect of this testing is the determination of the accuracy of the foam proportioning system. Where conditions permit, flow tests are to be performed. This includes measuring static water pressure, residual water pressure at the control valve and at a remote reference point, actual discharge rate, foam consumption rate, and foam concentration. This assures that foam is being discharged at the proper design rate and concentration. The concentration must be not less than the rated design concentration. It may not be more than 30% above the rated concentration or 1 percentage point above the rated concentration, whichever is less. After acceptance, an annual inspection is to be performed to determine that the system is still proportioning properly. Many jurisdictions prohibit or restrict the discharge of foam solution to the environment. In this situation, an alternative to a proportioning test using foam concentrate should be considered.