Friday, February 17, 2012

Reliable Electrical Power for Fire Pumps and Backup Power

When do you need backup power for an electric fire pump?  The simple answer is when the power is "reliable".  Of course the word reliable means a lot of different things to different people.  Interestingly, NFPA 20 did not define reliable power until the 2007.  Thankfully the committee did agree on the following language:
NFPA 20-2010
A.9.3.2 A reliable power source possesses the following characteristics:
(1) The source power plant has not experienced any shutdowns longer than 4 continuous hours in the year prior to plan submittal. NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, requires special undertakings (i.e., fire watches) when a water-based fire protection system is taken out of service for longer than 4 hours. If the normal source power plant has been intentionally shut down for longer than 4 hours in the past, it is reasonable to require a backup source of power.
(2) No power outages have been experienced in the area of the protected facility caused by failures in the power grid that were not due to natural disasters or electric grid management failure. The standard does not require that the normal source of power is infallible. NFPA 20 does not intend to require a back-up source of power for every installation using an electric motor–driven fire pump. Should the normal source of power fail due to a natural disaster (hurricane) or due to a problem with electric grid management (regional blackout), the fire protection system could be supplied through the fire department connection. However, if the power grid is known to have had problems in the past (i.e., switch failures or animals shorting a substation), it is reasonable to require a back-up source of power.
(3) The normal source of power is not supplied by overhead conductors outside the protected facility. Fire departments responding to an incident at the protected facility will not operate aerial apparatus near live overhead power lines, without exception. A back-up source of power is required in case this scenario occurs and the normal source of power must be shut off. Additionally, many utility providers will remove power to the protected facility by physically cutting the overhead conductors. If the normal source of power is provided by overhead conductors, which will not be identified, the utility provider could mistakenly cut the overhead conductor supplying the fire pump.
(4) Only the disconnect switches and overcurrent protection devices permitted by 9.2.3 are installed in the normal source of power. Power disconnection and activated overcurrent protection should only occur in the fire pump controller. The provisions of 9.2.2 for the disconnect switch and overcurrent protection essentially require disconnection and overcurrent protection to occur in the fire pump controller. If unanticipated disconnect switches or overcurrent protection devices are installed in the normal source of power that do not meet the requirements of 9.2.2, the normal source of power must be considered not reliable and a back-up source of power is necessary.

Interestingly for those of you who are insured by FM Global, the requirements are actually less stringent.
FM 3-7 (May 2010)
2.7.1.2 Supplement unreliable power sources with a second, independent source of power, such as an emergency generator or alternate utility connection, or provide a diesel engine-driven pump.
A reliable power source has infrequent power disruptions from environmental or man-made conditions. An electric power source that has disruptions lasting longer than 8 hours three or more times in a 12-month period is considered unreliable. More frequent short-term outages would also be considered unreliable.
The backup power can be from either an emergency generator or from a separate power system (unlikely).  So don't forget to select or a transfer switch or else change to a diesel engine driven fire pump.


Thursday, January 26, 2012

Pump Rotation

For a horizontal split-case fire pump the rotation is defined by looking at the drive side of the pump unit. This means that if you were sitting on the motor and looking at the pump, a right-hand (clockwise) rotation has suction on the right and a left-hand (counter-clockwise) has the suction on the left. Make sure that you verify your orientation when looking at the pump.

LH Counter Clockwise    |     RH Clockwise

Also don't forget there are no UL/FM listed "left hand rotation" diesel engines available on the market.

Tuesday, January 10, 2012

Diesel Fuel Tank Size for Fire Pumps

Guidance for the sizing diesel fuel tanks is quite straight forward due to the prescriptive requirements of the code.  Just take your engine HP x 1.10 and the result in gallons is the minimum required diesel fuel storage tank size.  The exact code reference from NFPA 20 (2010 edition) is provided below:
11.4.2* Fuel Supply Tank and Capacity.
11.4.2.1* Fuel supply tank(s) shall have a capacity at least
equal to 1 gal per hp (5.07 L per kW), plus 5 percent volume
for expansion and 5 percent volume for sump.
A.11.4.2 The quantity 1 gal per hp (5.07 L per kW) is equivalent
to 1 pint per hp (0.634 L per kW) per hour for 8 hours.
Where prompt replenishment of fuel supply is unlikely, a reserve
supply should be provided along with facilities for transfer
to the main tanks.
How the committee arrived at these simplified guidelines is as follows.  First, lets look at the conditions for when we expect the fire pump to run:

  • Quarterly Refilling of the Fuel Tank (approx 12-weeks)
  • A weekly test run for 30 Minutes
  • A minimum run time of 2-hour (or 4-hours during a fire depending upon your needs)
Multiply this out and you get basically 8-hours of continuous run time depending upon your run time during a fire.  Take the NFPA 20 appendix guidance of 1 pint/hr/HP (0.125 gallons/hr/HP) x 8 hours and you get 1 Gallon per horse-power.

Lets compare this to the actual published data for a specific diesel engine.  Take the smallest diesel engine Cummins makes a CFP5E-F10 which produces 95HP at 1760 RPM.  The published fuel rate is 4.9 Gal/hr (18.5 L/hr).  4.9 Gallons/hr x 8 hours x 1.10 (sump/expansion) = 43 gallons minimum.  If we use NFPA 20 guidance we would get 95 HP x 1 Gal/HP x 1.10 = 104.5 gallons minimum.  As you can see the for this specific example NFPA 20 is much more conservative.

The other item you need to verify is that the fuel tank complies with UL 142  as required by NFPA 20 (2010 edition) paragraph 11.4.1.2.1.  Fuel tank sizes are limited to 1320 gallons and the standard sizes available are as follows:



Nominal Tank Sizes (Gallons) Usable Volume (Gallons)
119 105
187 165
300 270
359 320
572 515
849 766
1100 993






Thursday, January 5, 2012

Seismic Design For Fire Sprinkler Systems - Part 2

Continued from Part 1 of seismic design for fire sprinkler systems.

After you have determined if you need seismic bracing, how do you determine the amount of Horizontal Seismic Force or Fp to apply?  (Hint - You can just go to our Seismic Calculator App and have much of the look up work done for you.)

STEP ONE - APPLICABLE STANDARDS AND CODES
Assuming that you are working in a jurisdiction that has adopted the International Building Code (IBC), you would start with section 1613.1 which states:
1613.1 Scope. Every structure, and portion thereof, including
nonstructural components that are permanently attached to
structures and their supports and attachments, shall be
designed and constructed to resist the effects of earthquake
motions in accordance with ASCE 7, excluding Chapter 14 and
Appendix l1A. The seismic design category for a structure is
permitted to be determined in accordance with Section 1613
 or
ASCE 7.
 Furthermore the International Mechanical Code (IMC) section 301.15 states:
301.15 Seismic resistance. When earthquake loads are applicable in accordance with the International Building Code, mechanical system supports shall be designed and installed for the seismic forces in accordance with the International Building Code.
Looking in the appendix of the 2009 edition of IBC (page 590), we can see that the 2005 edition of ASCE 07 or ASCE 07-05 is adopted.  So what is ASCE 07-05?  The name of the standard is "Minimum Design Loads for Buildings and Other Structures" and is published by the American Society of Civil Engineers (ASCE).


STEP TWO - DETERMINE THE FORCE FACTOR
ASCE 07-05 paragraph 13.3.1 is the applicable section for "nonstructural" components and provides the following formula for determining the horizontal design force (Fp) to be applied:
ASCE Formula
Most of the variables are already defined by NFPA 13 and/or ASCE 07-05 as follows:

Variable
Standard Value
Definition
ap
2.5
Component amplification factor from Table 13.6-1 (Seismic Coefficients for Mechanical and Electrical Components) – “Piping and tubing not in accordance with ASME B31, including in-line components, constructed of high or limited deformability materials, with joints made by threading, bonding, compression couplings, or grooved couplings”.
(Note the 2002 edition of ASCE 7 recommended ap = 1.0)
Rp
4.5
Component response modification factor from Table 13.6.-1 (same item as ap above)
(Note the NFPA 13 2002 TIA 02-1 recommended a Rp = 3.5)
Ip
1.5
Component Importance factor (Ip) per ASCE 7-05 13.1.3 “… The component importance factor, Ip, shall be taken as 1.5 if any of the following conditions apply: 1. The component is required to function for life-safety purposes after an earthquake, including fire protection sprinkler systems…”
(Note the NFPA 13 2002 TIA 02-1 recommended a Ip = 1.5)
z
-
Height in structure of point of attachment of component with respect to the base.  For items at or below the base, z shall be taken as 0.  The value of z/h need not exceed 1.0.
h
-
Average roof height of structure with respect to base.

As you can see the only missing pieces are the Height of Attachment (z), Height of Structure (h), and Five-percent damped design spectral response acceleration at short periods (Sds).

The calculated design force can be reduced by a factor of 1.4 because ASCE/SEI 7 is based on strength design, whereas NFPA 13 uses allowable stress design. Prior to the 2007 edition, all loads in NFPA 13 were at allowable stress levels with the exception of the buckling loads for brace members. In the 2007 edition, tables that contained the allowable loads on braces have been reduced to add a factor of safety appropriate to the use of allowable stress design



Monday, October 3, 2011

Earthquake Data for Canada

There is a site similar to USGS' for earthquake data in Canada available at:
http://earthquakescanada.nrcan.gc.ca/hazard-alea/interpolat/index-eng.php
Let us know if you are interested in having Anvil Fire update our Seismic Force Calculator App to include this information.


Sunday, September 25, 2011

Seismic design changes - 2012 IBC

DesignMaps Application and 2008 Design Data
USGS has released an updated DesignMaps application which is a great application.  However, before you start applying it to 2009 International Building Code please make sure to read their FAQ page which states:
This application should currently only be used to investigate which design values will likely be mandated in the future.

This recommendation by USGS is based on the hierarchy of the codes and standards, which is as follows:
2003 IBC2006 IBC2009 IBC2012 IBC
ASCE7-02ASCE7-05ASCE7-05ASCE7-10
USGS 2002USGS 2002USGS 2002USGS 2008

The DesignMaps application utilizes information from the 2008 USGS National Seismic Hazard Maps information.   For 2008 the hazard values in the Central and Eastern U.S. have been reduced by 10-25% in many cases, and most 1-second period ground motion values for the Western U.S. have also been reduced, in some cases by as much as 30%.

Example differences between 2002 and 2008 Design Data
Lets look at a comparison of several values based on the 2002 vs 2008 hazard values.  (Examples based  Site Class 'D' and Occupancy Category of 'II').
Atlanta, GA (Lat 33.7489954, Lng -84.3879824)
Data SourceSsS1SdsSd1Sds Design CatSd1 Design Cat
2002 Design Data0.2260.0850.2410.137BC
2008 Design Data0.1850.0900.1970.144BC

Sacramento, CA (Lat 38.5815719, Lng -121.4943996)
Data SourceSsS1SdsSd1Sds Design CatSd1 Design Cat
2002 Design Data0.5910.2440.5230.311DD
2008 Design Data0.6750.2940.5670.355DD

Casper, WY (Lat 42.866632, Lng -106.313081)
Data SourceSsS1SdsSd1Sds Design CatSd1 Design Cat
2002 Design Data0.3700.0770.3710.123CB
2008 Design Data0.2770.0740.2910.118BB
As seen in the last example for Casper, Wyoming, seismic bracing for fire sprinkler piping is not required based on which design criteria is applied.  The Sds value is 21% less in the 2008 values.  So whether you utilize the 2002 or 2008 hazard data can make a significant difference on your project.

Anvil Fire's Seismic Force Calculation App provides values based on the 2002 hazard values published by USGS and is basically identical to the Java Ground Motion Parameter Calculator provided by USGS.  Consult with your AHJ, but at this time we recommend that you follow USGS's recommendation to only use the DesignMaps application to investigate the requirements of the future 2012 International Building Code.

For more detailed information on how to determine the seismic design forces for fire suppression systems, please read our blog post on Seismic Design For Fire Sprinkler Systems.

Sunday, August 14, 2011

Expanded Seismic Data for On-line App


So that our clients outside of the continental United States don't feel left out, we have expanded our seismic ground motion data to include:

  • Hawaii
  • Puerto Rico/U.S. Virgin Islands

This data is from the USGS and is applicable for designs applying ASCE 7-05 as referenced by the 2006 and 2009 editions of IBC.  Visit our on-line fire sprinkler seismic calculation app and try it out for these locations.