What do the Codes say (because it seems no one really knows)?
Fire pump. The very words make some Clients shudder. Not only are fire pumps expensive (hence the shudder), but they are also grossly misunderstood. Some of the challenges that face an Engineer, Architect, or Owner with fire pumps is the fact that their requirements are shrouded in codes referenced by other codes referenced by other codes.
When water services have sufficient volume of water, but the flow test data suggests there is insufficient pressure available from the water utility, a fire pump comes into play. The fire pump will boost the pressure available from the utility to provide the pressure required to accommodate the fire sprinkler or standpipe system in a building. Fire pumps can be electric motor-driven or diesel engine-driven, but most of the time in the commercial environment we see electric motor-driven centrifugal pumps installed.
So, let's start at the top and review how the codes work in New Jersey (other jurisdictions are most likely similar). The New Jersey Uniform Construction Code references Subcodes that are adopted to set a standard for the design and construction of buildings. The current Building Subcode is an amended version of the International Building Code (IBC) (2009 Edition- but not for long). In Chapter 9 of the IBC, the Subcode sets the standard for when automatic fire suppression (sprinkler) systems are required. When they are required, the IBC references NFPA 13 (2007 edition) Standard for the Installation of Sprinkler Systems.
So, you check Chapter 9 of the IBC and it says you need sprinklers. Then you go to NFPA 13 and review the installation standard. NFPA 13 says when a fire pump is required, you need to follow NFPA 20 (2003 edition) Standard for the Installation of Stationary Pumps for Fire Protection (if you haven't noticed, when standards reference other standards that reference other standards, the referenced editions get older and older!).
NFPA 20 has some interesting requirements for fire pumps and fire pump rooms. For example, a fire pump room in a non-high rise, fully sprinklered building requires a 1-hour fire separation (oh yeah, and don't get started on trying to figure out how the fire ratings in NFPA standards correlate to the IBC requirements...). Another requirement in NFPA 20 is that the fire pump room requires direct access from the outside of the building or through a stair or corridor that matches the rating of the room. This makes it really challenging to shove the fire pump room into "found" space that used to be a storage room on a dead-end corridor, or newly "found" excavated space that was just fill below slab previously...
OK, so now this where NFPA 20 gets good. When a fire pump is powered by electricity it indicates if one source of power is not reliable you need to provide a second source (I guess it's OK to serve it with two non-reliable sources of power...). Now, this is in concert with the National Electric Code (NEC), NFPA 70 (New Jersey's Electric Subcode). If one of your sources of power is an onsite generator, NFPA 20 references NFPA 110 (sigh, I know) Standard for Emergency and Standby Power Systems. NFPA 20 indicates you need a Level 1,Type 10, Class X type generator (huh?), it also requires a minimum of 8 hours of fuel.
All right, let's breakdown the NFPA 110 classification. Class X means the runtime of the generator is defined by something else- luckily for us, we know the runtime is 8 hours. Type 10 means that the time from when the utility power is lost and the generator restores the power is at most 10 seconds. Finally, Level 1 means that if it fails, it could result in the loss of human life.
When dealing with generators, one of the most controversial points is in Section 5.1 of NFPA 110. This section outlines the energy sources. It allows diesel or other types of liquefied petroleum. It allows LP gas. It allows natural or synthetic gas, well with one exception: For Level 1 installations where the probability of interruption of off-site fuel source is high, on-site storage of an alternate energy source sufficient to allow full output of the generator is required...
Besides these standards, NFPA 70 mimics NFPA 20 by saying an electric motor driven fire pump requires a reliable source of power or multiple sources. That's about where the similarities end... The fire pump section of the NEC indicates that if you need a generator it refers to it as a standby generator (WHICH IN NO WAY CORRESPONDS DIRECTLY TO NFPA 110 CLASSIFICATIONS). However, elsewhere in the NEC an informational note indicates that emergency generators feed fire pumps, contradicting the previous language (AND AGAIN IN NO WAY CORRESPONDING DIRECTLY TO NFPA 110)... However, emergency generators (per NEC) require on-site fuel source, unless the Authority Having Jurisdiction approves an off-site fuel source.
What does this all mean? When you have a fire pump you are required to have a reliable source of power. If you do not have a reliable source of power, you need two sources. If you choose (choose is the key word) to have a generator provide a source of power for the fire pump, it is an emergency generator (per NEC) or a Level 1, Type 10, Class X generator (per NFPA 110). You most likely need a generator with on-site fuel source. If you really want a natural gas fired generator, the Authority Having Jurisdiction will need to determine whether the potential for natural gas interruption is high.
There is nothing that says, "when you have a fire pump and a generator, the generator needs to serve the fire pump." What you need to do is make sure your Engineering consultant is up to speed on the currently adopted building code, the older sprinkler standard, the older-than-that fire pump standard, the older-than-that-and-the-other-thing generator standard and ultimately coordinates with the Fire Subcode Official.
So, it's a mess and the only way to make it easier is to hire someone who knows these standards and will help you navigate the requirements.