NFPA 20 is the most important standard for the design of fire pumps (off of a private supply) and booster pumps (off of a public supply – city water). Fire protection engineers use this detailed standard to determine the design of the booster/fire pump needed for an automatic sprinkler system.
NFPA standards are updated on a three year basis. The 2010 version which has been recently released includes some changes to the 2007 version. The changes are as follows:
- New or better definitions were added:
- Jockey pumps or sometimes referred to as pressure maintenance pumps (PMP)
- Packaged fire pumps or prepackaged fire pump units
- The return of Chapter 4 on fire pumps in high rise buildings was added
- Information pertaining to jockey pumps and their pump sizing is provided
- In Chapter 5 a new section was added on prepackaged fire pumps
- FM approved flexible couplings are now available and are now required to be FM approved
- Chapter 10 on Electric Driven Control Units removed the section on limited service controllers
- Chapter 11 on Diesel Engine Drives was completely reworked as follows:
- The EPA standards have required cleaner emissions over the last few years and will require all diesel engines to meet very stringent emission standards
- Electronic Controlled Modules (ECM’s) are now required for fuel management
- In the past two manually operated ECM’s were required now two automatic ECM’s need to be provided on all diesel driven engines no matter when the engine was installed
- A new Contractor Material Test Certificate (CMTC) designed specifically for fire/booster pumps was added
Jockey pumps are sized and provided to replenish the fire protection system pressure due to the allowable leakage and normal drops in pressure or as NFPA 20 states “Shall have rated capacities not less than normal leakage”. How is anyone to know what the normal leakage rate is?
NFPA 20 does not intend to leave a leaking system. You should do a dry joint test at the required test pressures. These allowances give an indication of the loss of water that will take place over time due to earth movement, traffic, or soil settling.
NFPA 20 goes on to state that the maximum leakage per 100 joints is two quarts per hour, which translates into an estimated loss of approximately 14 gallons per hour. You also must allow for incidental leaking or use within the thousands of feet of pipe inside the facility. The standard requires the water and the pressure should be replenished within ten minutes. Taking the system pressure into account, your choice of pumps will be sized much larger than the water usage. High-pressure requirements in some sprinkler systems may require the pressure to be at 165-psi static pressure. That means the jockey pump will be required to deliver 20 gpm or more at 165 psi to meet the requirements.
What is Reliable Power?
The past editions of the NFPA 20 indicated that the power source to fire pumps must be reliable. So what was considered reliable?
You will not find a definition of a reliable power source within the NFPA 20 standard, past or present. The lack of information of how to determine reliability put installers, owners, and Authority Having Jurisdictions (AHJ’s) in situation that was up to interpretation. Some installations have resorted to installing generators or diesel driven fire pumps to resolve the reliability issue and this adds significant cost to the project and may make the cost benefit of an electrical pump versus a diesel pump a non-factor. Some jurisdictions went as far as requiring a backup power supply when an electric driven fire pump was installed.
NFPA 20 intent is that if a single reliable power source is available and used to drive the electric pump motor, nothing more is required such as an on-site generator. Fortunately, the annex Section A.9.3.2 was expanded in the 2007 edition and included in the 2010 edition of NFPA 20 on how to determine the reliability of the power supply to a fire pump by evaluating four different characteristics. If any of the following cannot be met than a back up reliable power supply is necessary.
1. If a plant sustained a power outage longer than four (4) hours in the year prior. In the 2008 NFPA 25 edition the impairment requirements changed to ten (10) hours but this time outage was not adopted in the 2010 version of NFPA 20 for a time requirement for back up power.
2. The power grid has known failure problems.
3. If the power supply is fed by overhead conductors than the fire department may have to cut them to utilize their aerial apparatus.
4. Only the disconnect switches and overcurrent devices can be installed in the normal source of power. Power disconnect switches and activated overcurrent protection should only occur in the fire pump controller. If this can not occur than additional disconnect switches and activated overcurrent protection will be installed deeming the existing power supply unreliable.
NFPA 20 is a very detailed standard on fire and booster pumps. A well trained fire protection engineer can help provide engineering consulting services with regard to NFPA 20 and the recent changes. We at Risk Logic are well trained with regard to NFPA 20 and can provide these services for you.