Thursday, April 25, 2013

Fire Pump Sensor Recall

Gem Sensor 3100 Recall Notice

Gem Sensor - Old 3100 model
Gem Sensor - Model 3300 (new)
On April 24, 2012 the Consumer Product Safety Commission (CPSC) issued a press release, CPSC #12‐156, for the voluntary recall of Gems 3100 Pressure Detectors/Transducers because the transducer can fail to accurately detect water pressure in a fire suppression sprinkler system. This could cause the sprinkler system to fail to activate and pump water to the sprinklers in the event of a fire. The failure associated with the Transducer is not a sudden loss of function but rather a slow degradation of performance over many hours of continuous use with constant water pressure. The use of the transducer in non‐water and/or fluctuating pressure applications has not shown the same potential problem.

The sensors are basically failing in a "high" pressure rating (e.g. will read 100 PSI higher than actual pressure).  So it is easy to spot, but does require good on-going maintenance.  One should install a calibrated gauge and compare the pressures.

The transducer has "Gems Sensors & Controls," as well as the 18- digit part number, printed on a label affixed to the center of the transducer. Part numbers beginning with "3100" are included in this recall.

Gems sold the recalled 3100 Pressure Transducers directly to end-users and through distributors from January 2006 through February 2012.

The 3100 has been replaced with the new 3300 series model.  Replacement transducers are avaliable at no cost from Gem.

The newer 3300 model has a green sticker as shown in the figure to the right.  The older 3100 model has a white sticker.



U.S. Consumer Product Safety Commission

Office of CommunicationsWashington, D.C.

April 24, 2012
Release #12-156
Firm's Recall Hotline: (855) 877-9666
CPSC Recall Hotline: (800) 638-2772
CPSC Media Contact: (301) 504-7908

Gems Sensors Recalls Pressure Transducers Used in Fire Pump Controllers Due to Risk of Failure in a Fire

WASHINGTON, D.C. - The U.S. Consumer Product Safety Commission, in cooperation with the firm named below, today announced a voluntary recall of the following consumer product. Consumers should stop using recalled products immediately unless otherwise instructed. It is illegal to resell or attempt to resell a recalled consumer product.

Name of Product: Gems 3100 Pressure Detectors/Transducers

Units: About 25,000

Importer: Gems Sensors Inc., of Plainville, Conn.

Hazard: The transducer can fail to accurately detect water pressure in a fire suppression sprinkler system. This could cause the sprinkler system to fail to activate and pump water to the sprinklers in the event of a fire.

Incidents/Injuries: None.

Description: The Gems 3100 Pressure Transducer is used to detect pressure in a range of applications, including the detection of water pressure as part of a fire pump controller in a fire suppression sprinkler system. The transducer has "Gems Sensors & Controls," as well as the 18- digit part number, printed on a label affixed to the center of the transducer. Part numbers beginning with "3100" are included in this recall.
Sold by: Gems sold the recalled 3100 Pressure Transducers directly to end-users and through distributors from January 2006 through February 2012 for about $250.

Manufactured in: England

Remedy: Contact Gems to receive enhanced twice monthly inspection instructions and information about a free replacement transducer, when warranted. End-users who use the 3100 Pressure Transducer in other applications in which water pressure is measured should contact Gems to determine if their units are affected.

Consumer Contact: For additional information, call the company toll-free at (855) 877-9666, between 8 a.m. and 4:30 p.m. ET, Monday through Friday, or visit the firm's website at

Gems 3100 Pressure Transducer

Gem Sensor - Old 3100 model

The U.S. Consumer Product Safety Commission (CPSC) is still interested in receiving incident or injury reports that are either directly related to this product recall or involve a different hazard with the same product. Please tell us about your experience with the product on

CPSC is charged with protecting the public from unreasonable risks of injury or death associated with the use of the thousands of consumer products under the agency's jurisdiction. Deaths, injuries, and property damage from consumer product incidents cost the nation more than $900 billion annually. CPSC is committed to protecting consumers and families from products that pose a fire, electrical, chemical, or mechanical hazard. CPSC's work to ensure the safety of consumer products - such as toys, cribs, power tools, cigarette lighters, and household chemicals - contributed to a decline in the rate of deaths and injuries associated with consumer products over the past 30 years.

Under federal law, it is illegal to attempt to sell or resell this or any other recalled product.

Thursday, March 15, 2012

Pressure Relief Valves with Diesel Engines

Photo of Circulation Relief Valve
Circulation Relief Valve
When is a pressure relief valve (PRV) required on a fire pump system?  For a standard 175 PSI rated system, the simple answer is check and make sure that your expected churn pressure plus maximum static suction pressure will not exceed 144.6 PSI (or 206.6 PSI for a 250 PSI rated system).  The sizing of the relief valve comes from NFPA 20 (2010 edition) table 5.25(a) which is summarized in our fire pump sizing app.  For those of you that like to know the details read on.

First let's clarify that we are taking about a main pressure relief valve and not a circulation relief valve.  A circulation relief valve is generally 3/4-inch in size if less than 3,000 gpm and intended to provide a little fresh water into the pump casing for cooling purposes.

photo of main pressure relief valve for fire pumps
Pressure Relief Valve
When we say pressure relief valve in "fire pump" terminology, we are referencing a PRV that is only provided on diesel fire pumps to accommodate possible engine over-speed conditions.  The regulators on diesel engines are good, but not perfect.  When the load on the diesel engine changes,there is a natural delay in response and overshoot while the engine tries to maintain speed.  Our goal is prevent the system from exceeding maximum rated system-pressures when this slight change in RPM occurs.  By code diesel fire pumps have a kill switch should the RPM exceed ten-percent of the design speed.  In practice, we have rarely seen a well maintained engine exceed 1.5% of the required speed when adjusting for loads.

So how does this 10% maximum permitted over-speed RPM relate to the output pressure?  The speed (RPM) of a fire pump and the pressure developed do not increase linearly.  That is if you double the RPM you do not double the pressure.  When you double the speed you actually get four times the pressure.  The formula is written as follows:

Pump Speed vs. Pressure Affinity Formula
Pump Speed vs. Pressure Affinity Formula - Rearranged

If we square the 10% increase in speed, we get a 21% increase in pressure as shown below.  If we take 144.6 psi * 121%, we get 175 PSI.  In practice, we do not recommend running your system this close to the rated system pressure unless you know there will never be any change to your suction pressure (i.e. a vertical turbine fire pump).  For diesel fire pumps we recommend that you call and talk to one of our sales engineers.
The NFPA 20 fire pump committee did this exact same exercise and came up with the following language for the code:
NFPA 20 – 2010 Edition
4.18.1* General. Where a diesel engine fire pump is installed and where a total of 121 percent of the net rated shutoff (churn) pressure plus the maximum static suction pressure, adjusted for elevation, exceeds the pressure for which the system components are rated, a pressure relief valve shall be installed.

FM Global Standard 3-7 (Fire Protection Pumps – May 2010)
2.3.3 Pressure Relief Valves Provided a main relief valve on all diesel engine-driven fire pumps when 121% of the net rated shutoff (churn) pressure plus the maximum pump static suction pressure exceeds any system component rated pressure.
FYI - Remember that utilizing a Pressure Relief Valve to reduce discharge pressures is not permitted by NFPA 20 section Designing system to discharge large amounts of water every time it runs is not considered good design practice and code recognizes this fact.

Friday, February 17, 2012

Reliable Electrical Power for Fire Pumps and Backup Power

* Note that the 2016 edition of NFPA 20 changed the 4-hour to 10-hours of continuous outage *

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) 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.* 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  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.)

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
 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).

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:

Standard Value
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)
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)
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)
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.
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:
Let us know if you are interested in having Anvil Fire update our Seismic Force Calculator App to include this information.