Fire protection pumps: Updates to NFPA 20
Water mist pumps
Water mist technology is starting to be accepted to protect hazards that traditionally have been protected by sprinkler systems. For some of these applications, multiple water mist pumps are arranged in parallel to operate as a unit, with additional pumps turned on as additional nozzles operate. In some applications the small water mist pumps are mounted on the same frame and designed with variable speed operation capability. NFPA 20 has traditionally treated fire pumps as individual units and made requirements accordingly. Even in applications such as refineries and aircraft hangers, where multiple fire pumps must operate to supply the full demand, NFPA 20 requires an independent controller, pump test header, and pressure relief valve (if required) for each unit.
Water mist pumps are low-volume pumps that develop medium to high pressures. Because these pumps operate as a single unit, the NFPA 20 committee felt that it was appropriate to add requirements that better fit a “unit” concept. A definition of a “water mist positive displacement pumping unit” was added to allow water mist pumps operating in parallel to be treated as a unit. A significant change allows a single controller to be used for water mist pumps operating in parallel as a “water mist positive displacement pumping unit.” Another change allows a “water mist positive displacement pumping unit” to serve as a jockey pump. In order to assure that a “water mist positive displacement pumping unit” serving in a jockey pump mode generates a signal and switches to a fire pump mode when a nozzle operates, the jockey pump mode cannot provide more than half of the nozzle flow of the smallest system nozzle when the standby pressure is applied at the smallest nozzle.
Special treatment was required for pump curves. The manufacturer must provide both individual and unit fire pump curves with and without variable speed features deactivated.
Diesel fuel oil
An expert gave a presentation on the changes in diesel fuel oil to the NFPA 20 committee. As the industry moves toward biodiesel (especially in Europe), the long-term storage of diesel fuel required for diesel driven fire pumps requires more attention. Bio-based diesel fuel is more susceptible to "bugs” than petroleum-based diesel fuel and is not intended for long-term storage before consumption. Regular inspection and testing are required to make sure deterioration of the fuel will not adversely affect the diesel engine. A requirement for providing a listed active fuel maintenance system on fuel tanks was passed by the NFPA 20 committee but overturned at the NFPA technical session. This leaves the 2013 edition of NFPA 20 with minimal guidance for maintaining diesel fuel.
A significant reason for overturning the requirement for a listed active fuel maintenance system was to allow for other options. This is an international issue that likely will be addressed in the 2016 edition of NFPA 20.
Series fire pump operation
An ongoing debate has developed over allowing vertical staging of fire pumps that operate in series. The debate continued to the NFPA technical session, with the final result that vertical staging is still permitted. A detailed discussion of the issues involved with vertical staging of fire pumps is included in “Fire Pumps In High Rise Buildings” in the July 2009 edition of Consulting-Specifying Engineer.
The primary reason for vertical staging of fire pumps is perceived lower cost. In general, non-vertically staged fire pumps will require two express risers to the supply the higher zone that could be supplied through standpipe risers on vertically staged fire pumps. However, vertically staged fire pumps will require a pump test riser from the higher floor to an appropriate discharge location probably on the ground floor, and also requires running electrical power with a 2-hour fire rating requirement to the vertically staged fire pump. The actual cost difference may be minimal and should be evaluated on a case-by-case basis considering the cost impact of both piping and electrical supplies.
It is likely that this issue will be readdressed in the 2016 edition with the possible addition of remote operational capabilities to address emergency operation issues.