The use of fire pumps for fire protection is certainly not new – the initial NFPA Technical committee to establish uniform guidelines for proper and effective installation of fire pumps dates back to 1899. Over the years there have been many changes leading to the current standard.
Water based fire protection systems are an important part of safety and loss control, both to life and property. As such, a high degree of reliability and effectiveness are essential, and this extends to fire pumps – which can provide an element of the system to furnish water flow and pressure in support of the overall system or in some cases a second water supply for redundancy.
In general, changes in each edition of the standard are the result of several broad categories such as enhancement and refinement of existing information, reaction to technology in the equipment and in other elements of the overall system, changes to correlate with other standards revisions and resolution of questions from users. Lately the inclusion of performance based philosophy in parallel with proscriptive requirements is another reason. In the evolution of the current standard some significant changes were made, which expanded the scope from horizontal centrifugal pumps to vertical shaft pumps, variable speed pumps and positive displacement pumps. In each instance, there is a ripple effect throughout the standard to outline proper installation, control instrumentation alarms, etc. The latest edition contains a number of changes, and the significance of the various changes to individual users may be different. Several have been selected for discussion but the level of detail discussed may be considered overdone by some and treated too lightly by others. This is the result of our own perspective and interests.
Changes in automatic sprinkler technology have resulted in favorable design options with the drawback that high system pressures can result from the use of fire pumps in the most typical arrangements. A booster pump can develop significant pressure at low or no flow (churn) conditions. This has become fairly common in warehouses with ESFR sprinklers. Pressures can exceed 200 psi where system components are typically rated for only 175 psi. Historically, a common way to prevent system over pressurization was to install a main (full flow) relief valve. This valve would open before the system reached dangerous pressures.
Using a relief valve or pressure reducing valve in the pump discharge piping for routine pressure control was specifically prohibited by NFPA 20 in 2003 as a poor design practice. Main relief valves are still required in certain circumstances, but they cannot be installed simply to prevent overpressure from a pump that, by design, would be expected to over pressurize the system. There are alternative solutions.
Pressure reducing valves can be used downstream of the pump discharge control valve. Components rated for higher pressure ratings can be used, upstream of the pressure reducing valve or throughout the system. A variable speed pump driver can be used, which would yield lower net pressure boost at lower flows while still providing adequate pressure at higher flows. Since pump discharge pressure is proportional to pump driver speed, overpressure can be managed by reducing the engine speed when the pump is operating at churn or low flow conditions. A relief valve is still required but this is a safety measure, not the primary means of overpressure control. Excess pressure may be avoided altogether by careful selection of automatic sprinklers combined with pipe sizing and hydraulics such that a pump, if needed, does not have to over pressurize the system at the lower flows. The use of a pump suction tank could reduce the static pressure on the pump suction side and result in lower discharge pressure at low flow conditions. Somewhat akin to this is the use of a Break Tank. Certainly, break tanks are not a new creation, but in the context of over pressurization, they provide a much lower cost alternative to a suction tank for reducing the static pressure seen at the pump suction. In order to introduce this alternative, NFPA 20 has included a wide variety of requirements associated with tank size as relates to fluid withdrawal rate, refill mechanisms, minimum tank level, number of and capacity of refill systems, automatic and possible manual refill capability, level signals and alarms.
When dealing with fire pumps, especially electric drive, the power supplies are of key importance. Reliability of the supply has been an issue for many years. Definition of “reliable” can be arbitrary and attempts have been made to clarify the term. This includes no shutdowns longer than 4 hours at the source power plant in the year prior to submittal of the installation plans, no grid failures that caused outages in the area of the protected property, normal power source is not overhead conductors directly outside the facility, only disconnect switches and normal protective devices permitted by NFPA 20 are installed in the normal power. It is not unlikely that the definition of “reliable” will be an ongoing source of revision. If considered not reliable, there are alternatives such as a second independent utility source, on site power generation or a standby generator or a second pump with diesel engine drive. While some users of NFPA 20 will be looking for strict code compliance, others may be balancing the risks to property with the costs of higher levels of reliability – the answers may be arbitrary.
The terms “Alarm” and “Signal” have been re defined to distinguish the intent of NFPA 20 that an alarm is not necessarily a situation which requires an action by the fire department. This was felt necessary since the National Fire Alarm Code (NFPA 72) has definitions of similar terms with differing resultant actions. Once established, the entire document was changed wherever the terms were being used to make sure the proper definitions were referred to, depending on the action the code intended.
The interface between a power utility and a site relate to the National Electric Code (NFPA 70) and NFPA 20, respectively. Should a utility install a phase converter, this is considered acceptable and outside the scope of NFPA 20. However, the site is not permitted to install a phase converter in NFPA 20. Attempts are made to more clearly define the interface as can be seen by the many references to NFPA 70.
Fixed emergency lighting based on the Life Safety Code is now required in a fire pump room.
Other Items of Note
Qualified Personnel – a qualified person is supposed to respond to the fire pump room while the pump is operating. This includes during a fire. The definition of “qualified person” has been revised. This is the type of change that will likely be revised several times over in the future.
When the qualified person responds, he may not have access or egress via the exterior. While this is highly encouraged in the code annex, it was not made a requirement.
The need for fire rated cut off rooms and the specific fire rating, with and without sprinkler protection, have been defined. Certain situations are have requirements regarding mandatory ratings and sprinklers others have optional tradeoffs – tables are provided for assistance with the determinations. Also included was a 2 hour fire rating for pump rooms in sprinklered hi rise buildings.
A clarification was included that combustibles or storage are not allowed in pump rooms, but other mechanical equipment can be in the room as long as the fire hazard does not increase as a result.
Risk Logic, Inc. has the capability to evaluate your existing or planned fire pump installation for conformance, or to develop and recommend appropriate designs. We are available to assist you with your fire protection needs and look forward to that opportunity.