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CODE UPDATE

The 2003 Edition of NFPA20 now allows the installation of "variable speed pressure limiting controldevices". These devices are an option for systems with static pressures close to the maximumworking pressure of the system. Such devices are available for both diesel and electric driven pump.It is recommended to contact an expert when applying such a device to ensure proper co-ordinationof equipment. For more information, visit the link below, or read more about the application in PMEngineer Magazine's February 2004 Issue.

INDUSTRY NEWS

The Loss Prevention Certification Board has published a standard on diesel engines for fire pumpservice. Such engines are now required by code on any LPCB certified sprinkler system. The productis available and the rules went into effect on April 1st of 2004.

HIGH-RISE FIRE PROTECTION SYSTEM DESIGN: ZONING & SERIES PUMPING

This article is the first of a series of articles on high-rise fire protection system design.

Anyone who lives in an urban center these days understands the drawbacks of traditional urbanplanning. As cities around the world grow, traffic jams add hours to commuting times, thusdegrading the quality of urban life. Green space is paved over to make way for parking garages andcommercial construction. More and more, municipalities and urban planners are working together tomanage urban sprawl. Though public transit provides one facet to the solution, anotherconsideration is building more vertically to better utilize precious space.

Traditionally, high-rise buildings were a rarity in most metropolitan areas. A lack of experience inbuilding design presents a challenge to engineers around the world. Many hard-earned lessons indesigning high-rise buildings can be learned by studying cities which have always had the urbansprawl problem - such cities have experienced the problem of building high-rises for decades.

High-rise buildings present especially difficult challenges for fire protection:

Rapid and safe egress from the building in the event of a fireIntegrated alarm systems to alert occupants of an emergencyEntry to the building for the fire departmentDistribution of adequate water flow where it is needed under the right pressure

Taking a traditional approach to water distribution for fire systems can be impractical, costly, anddecrease system reliability. The traditional water distribution system in a building involvesdesigning around a single zone piping system. Doing so results in many design challenges, the mostserious of which is pressure regulation in the system.

Why zone the fire protection system?Prior to 2003, fire protection engineers had little to go by in assisting in high-rise standpipe systemdesign other than a very good, but often overlooked diagram in the Appendix of NFPA14. Chapter 7of NFPA14 2003 was greatly expanded to better explain how to design zoned standpipe systems forhigh-rise buildings. Zoned systems are recommended in high-rises due to the fact that zoningallows design of a system where the maximum static pressure in most of the system is lower than

175psi. What are the benefits of this design? They are numerous.

Taken from NFPA14: The Standard for the Installation of Standpipeand Hose Systems - 2003 Edition

Before going into the benefits of zoned system design, we must examine the requirements forstandpipe systems. NFPA14 sets constraints on the maximum static and minimum residual pressureat the most hydraulically remote hose connection. These constraints are based on whether the hosesare for occupant use (1.5" hoses) or for fire department use (2.5" hoses). In the past, standpipesystems generally had one or the other type of hoses, and were classified as Class II and Class Istandpipe systems, respectively. Most high-rise commercial or residential buildings today aredesigned with a Class III standpipe system. The Class III system is characterized by hose cabinetscontaining one 1.5" hose connection with 50 feet of hose and one 2.5" valve with no hose. NFPA14'sdesign pressure range for 1.5" valves is 65psi to 100psi. For 2.5" valves, 100psi to 175psi is theconstraint. The reason for these constraints is to give occupants and fire fighters a relatively safe tooperate 100gpm hose stream to attack a fire with. For more challenging fires, the fire departmenthas access to a 250gpm hose stream under higher pressure at the 2.5" connections.

It is not difficult to see that the Class III standpipe system in a high-rise is going to require a largenumber of pressure regulating devices in order to maintain adequate water flow and pressurewithout endangering the operators of the equipment.

By zoning the system, a large number of pressure regulating devices can be eliminated in thesystem. This has broad-reaching implications for installers, designers, building owners, buildingoccupants, and ultimately, the fire department.

1. First Cost: Apart from eliminating the actual pressure regulating devices, every standpipe withpressure regulating devices is required to have a drain riser. By zoning the system, the drain riserand test plumbing can be eliminated for the cost of adding an express riser for the high zone watersupply.

2. Reliability: Elimination of restricting or regulating devices removes a potential failure mode ofthe system. There is no concern for valve failure - the water supply has a "straight shot" to the hoseconnection in use during the fire.

3. Redundancy: With the zoned system, there are two sets of distribution piping to service thebuilding. If one zone becomes inoperable due to over-pressurization or a mechanical failure of avalve or pump, there is a second set of piping to distribute water for the fire department.

4. Maintenance: Elimination of pressure regulating devices reduces the maintenance requirementsfor the system. Each pressure regulating device must be inspected quarterly. Further, each valverequires a full flow test every 5 years.

5. Function: The final question becomes quite simply, "Who's standpipe is this anyway?". In thedesign mode, engineers generally consider the water distribution piping to be a means for meetingcode requirements and to service automatic sprinkler needs. Though the water distribution pipingdoes service the automatic fire system, the main purpose of the standpipe system is to give the firedepartment water, be it from an automatic fire pump, or from the hydrants and pumper trucks onthe street. The standpipe belongs to the fire department as much as it belongs to the buildingowner. When designing the system, redundancy and reduction in potential failure modes should bethe major cause for concern. We should primarily consider the reliability of the distribution systemfor the fire department itself. A zoned system can guarantee adequate water flow and pressurewithout endangering fire fighters by supplying water under too high pressure, leaky piping, or (inthe worst case) no water at all. The zoned system fits the bill for this design.

The next issue of this newsletter will examine a zoned system design and look at sizing of firepumps for high-rise buildings.

FIRE PUMP TIPS

Question: What is the purpose of a casing relief valve on a fire pump?

Answer: NFPA20 requires a listed casing relief valve on any electric fire pump. Water cooled dieselengine driven fire pumps do not require this valve. The cooling water supplied to the diesel servesthe same purpose as a casing relief valve on electric pumps. The reason for installing a casing reliefvalve is that a fire pump running at no-flow conditions very rapidly heats the water in the pumpcasing. This is due to a number of factors: low hydraulic efficiency when operating at shut-off, smallcasing water volume, and the relatively high horsepower being applied to the pump. Where a casingrelief valve is not installed or is set improperly, it is not unusual for a pump to boil the water in thepump casing resulting in steam burning the packing, destroying gaskets and o-rings, and damagingthe bearings.

The casing relief valve should installed between the pump discharge flange and discharge checkvalve. It should be set such that it is closed when the fire pump is not running and open when thepump is running. Typically, about 1% or less of the fire pump rated flow is enough to prevent thewater in the casing from boiling. Flow through the packing also contributes to cooling. It isrecommended to set the casing relief valve with the pump running at no-flow such that thedischarge water temperature stays below 40 degrees C (104 degrees F). There is no need tomeasure this temperature to set the casing relief valve. After running the pump with water flowthrough the casing relief valve, the discharge (waste) pipe should feel warm to the touch but nothot when the proper flow is discharging from the valve.

NEW FROM ARMSTRONG

Check out Armstrong's new range of LPCB approved end suction pumps rated up to 9000lpm atpressures up to 10 bar. For more information, contact Armstrong Pumps Ltd. at Tel: 01206-579491/ Fax: 01206-760532.