Information Notice 2002-24, Potential Problems with Heat Collectors on Fire Protection Sprinklers
| ML022000376 | |
| Person / Time | |
|---|---|
| Issue date: | 07/19/2002 |
| From: | Beckner W, Pierson R Office of Nuclear Material Safety and Safeguards, NRC/NRR/DRIP/RORP |
| To: | |
| Petrone C , NRC/NRR/RORP, 415-1027 | |
| References | |
| TAC M3554 IEIN-02-24 | |
| Download: ML022000376 (14) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001 July 19, 2002 NRC INFORMATION NOTICE 2002-24: POTENTIAL PROBLEMS WITH HEAT
COLLECTORS ON FIRE PROTECTION
SPRINKLERS
Addressees
All holders of licenses for nuclear power, research, and tests reactors and fuel cycle facilities.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert
licensees to potential problems with using heat collectors on sprinklers and fire detectors
installed to satisfy NRC fire protection requirements. It is expected that recipients will review
the information for applicability to their facilities and consider actions, as appropriate. However, suggestions contained in the IN are not NRC requirements; therefore, no specific action or
written response is required.
Background
NRC fire protection engineers and inspectors have recently raised technical concerns regarding
the adequacy of sprinklers that rely on metal plates, commonly referred to as heat collectors, to activate (see Figure 1 in the attachment). When convective heat energy rises above the fire
plume, it terminates its vertical movement at the ceiling and flows past the sprinklers heat- sensitive element. This flow of heat across the ceiling is called the ceiling jet. The ceiling
directs the convective heat energy horizontally towards the sprinklers nearest the fire. If the
sprinklers heat-sensitive element is a fusible link, the heat melts the link, releasing water to
control the fire. If the sprinklers heat-sensitive element is a glass bulb, the heat expands the
liquid in the glass bulb until the bulb breaks, releasing water to control the fire.
Heat collectors were intended to reduce the time a fire takes to activate sprinklers located too
far below the ceiling. When sprinklers are too far below the ceiling, most of the heat energy
rises past the sprinklers and heat collectors and the sprinklers are not activated. Locating the
sprinkler close to the ceiling ensures that the sprinkler will be in the hot gas layer, minimizing
activation time and enabling the sprinkler to provide a fully developed water spray pattern to
control the fire. In addition, the water from the sprinkler cools the upper gas layer (preventing
flashover conditions) and cools the structural steel supports of the compartment boundaries
(preventing structural collapse).
In the late 1970s and early 1980s, some sprinkler system designers and fire protection
engineers supported the opinion that sprinklers could be placed far below the ceiling if heat
collectors were installed above them to help activate them during a fire. They reasoned that
heat from the fire plume can create temperatures or draft conditions that cause water droplets
to evaporate before penetrating and cooling the plume and that large clearances between
sprinklers and floor-level combustibles could aggravate the problem of ensuring that the correct
sprinkler water density is available from sprinklers. Therefore, they installed heat collectors so
that sprinklers could be closer to the combustibles at floor level.
Other sprinkler system designers and engineers thought that ceilings were too congested with
cable trays, conduits, piping, ductwork, etc., and that sprinklers could be mounted below these
ceiling-level obstructions to develop adequate spray patterns. The 1999 edition of National
Fire Protection Association (NFPA) 13, Standard for the Installation of Sprinkler Systems, provides requirements for the installation of sprinklers under obstructed ceilings. NFPA 13, Section 5-6.4.1.1, states that under unobstructed construction, the distance between the
sprinkler deflector and the ceiling shall be a minimum of 1 in. (25.4 mm) and a maximum of 12 in. (305 mm). In certain cases NFPA 13 allows sprinklers to be placed as far as 22 inches
below an obstructed construction. NFPA 13 also requires sprinklers to be installed below fixed
obstructions and to provide full ceiling-level sprinkler coverage1. These NFPA 13 requirements
appear to be consistent with the requirements of NFPA 13 from the early 1980s.
Generic Letter (GL) 86-10, Implementation of Fire Protection Requirements, provides
guidance on sprinkler location. Section 3.4.3, Sprinkler Location, and Section 3.4.5, Sprinkler
Head Location, state that sprinkler system designs should meet NFPA 13 and be located at the
ceiling. The GL also states that in order to achieve complete area wide coverage, sprinklers
should be located at the ceiling, with additional sprinklers provided below significant
obstructions such as wide HVAC ducts and shielded or solid bottom stacked cable trays. To
the extent that an existing or proposed sprinkler system deviates from this concept, the design
would have to be justified by a fire hazards analysis. GL 86-10 provides no heat collector
guidance.
NFPA 13 contains no guidance or requirements regarding the installation of heat collectors in
lieu of a ceiling. To understand the origins of the heat collector concept, the NRC staff
examined previous editions of NFPA 13. The staff discovered that NFPA 13 has never
permitted, required, or taken a formal position on the installation of heat collectors installed
above sprinklers in lieu of locating the sprinklers close to the ceiling. The term heat collector
was first used in the NFPA 13 standard up to the 1963 edition and was listed in the index of
NFPA 13 up to the 1974 edition. The term first appeared in the NFPA 13 section on Guards &
Shields for protecting sprinklers. The staff discovered no references to heat collectors in any
editions of the NFPA 13 section that address the distance of sprinklers from the ceiling. Heat
collectors was changed to baffles in the 1963 edition during the NFPA document revision.
NFPA 13 was completely revised again in 1973, and baffles became shields.
NFPA 13 makes it clear that there are acceptable uses of shields. Shields are very similar in
design to heat collectors. Shields are metal plates installed over sprinklers in midair in fire
areas where full ceiling-level sprinkler protection is also provided. Shields function solely to
protect the midair sprinklers from cold-soldering. The cold-solder effect occurs when an
1 NFPA 13, Section 5-5.5.3.1, 1999 edition, states that sprinklers shall be installed under fixed
obstructions over 4 ft (1.2 m) wide such as ducts, decks, open grate flooring, cutting tables, and
overhead doors. operating sprinkler (usually at the ceiling) wets midair sprinklers, delaying or preventing their
activation. The wetting prevents the midair sprinklers from fusing (opening) to release water.
Sections 6-4 and 7-4 of NFPA 231C, Rack Storage of Materials, state that water shields shall
be provided directly above in-rack sprinklers, or listed sprinklers equipped with water shields
shall be used where there is more then one level, if not shielded by horizontal barriers.
NFPA 13 also provides guidance on the use of shields to prevent mechanical injury to
sprinklers and protect sprinklers under open gratings.
The first tests of heat collectors were apparently the tests conducted for the U.S. Atomic Energy
Commission (AEC, the predecessor to the NRC) by Union Carbide at the Oak Ridge Y-12 Plant
and documented in a 1973 report. Union Carbide tested sprinklers with and without canopies
(i.e. heat collectors) for response above kerosene fires. In the spring 1989 Sprinkler Quarterly, Russell P. Fleming contended that heat collector testing at the Oak Ridge Y-12 plant was
flawed. Fleming concluded that the test scenario placed the heat collector and standard
response sprinkler 3 feet above the kerosene fire, so that the sprinkler mainly activated by
radiant heating. In a more realistic fire scenario the sprinkler would be activated primarily by
convective heating.
Similar findings were reported in a January 1990 report, A Study of the Utility of Heat
Collectors in Reducing the Response Time of Automatic Fire Sprinklers Located in Production
Modules of Building 707, prepared for the U.S. Department of Energy Rocky Flats Plant by
Hughes Associates, Inc. (HAI). HAI conducted small-scale and large-scale testing for the
Rocky Flats Plant to determine if heat collectors directed enough of the convective heat of the
fire plume past sprinklers to activate them. HAI also studied the effect of using a quick- response sprinkler in lieu of a standard-response sprinkler with a heat collector. The results of
the HAI tests for the Rocky Flats Plant are summarized below:
- Heat collectors with the edges turned down around the side produced a dead air space
and the sprinklers had longer response times than sprinklers with a flat heat collector2 (see Figure 2 in the attachment).
- The heat collector must be in the plume to be effective. If the centerline of the fire is
more than 1 to 2 feet from the edge of a flat heat collector, a standard-response
sprinkler may take longer to respond, regardless of its thermal sensitivity.
- If a fire is midway between two sprinklers, the sprinklers may not respond at all
(regardless of the size of the heat collector) because the sprinklers are not exposed to
the convective heat flow of the ceiling jet.
2 This also applies to fire detectors with heat collectors. Dead air spaces under heat collectors
can prevent fire detectors from activating during the incipient stages of a fire. * Quick-response sprinklers activate more quickly than standard-response sprinklers only
if the fire was directly underneath the heat collector.3
Description of Circumstances
The primary objective of the fire protection programs at U.S. nuclear power plants (NPPs) is to
minimize the probability and consequences of a fire in accordance with General Design
Criterion 3 of 10 CFR Part 50, Appendix A. To meet these objectives, the fire protection
programs at NPPs must provide reasonable assurance, through defense-in-depth, that a fire
will not prevent the performance of necessary safe-shutdown functions and that radioactive
releases to the environment will be minimized. Part 10 to the Code of Federal Regulations
(CFR), Section 50.48, Fire protection, and 10 CFR Part 50, Appendix R, Fire Protection
Program for Nuclear Power Facilities Operating Prior to January 1, 1979," require that
automatic fire suppression systems be installed in certain fire areas to protect separated or
redundant trains of safe-shutdown equipment and circuits or to protect against a fire hazard.
NRC is concerned about the adequacy of sprinklers with heat collectors because NRC
inspectors have found a lack of technical documentation, tests, or calculations to support the
installation of sprinkler systems with heat collectors in fire areas. In addition, NRC inspectors
have found that some licensees have not performed an engineering evaluation to justify the
installation of heat collectors at their facilities.
NRC plant walkdowns have identified other heat collector concerns. One concern is the
location of sprinklers with heat collectors located below the primary combustible source (i.e.,
cables installed in cable trays). In this configuration, if a cable fire occurred, the sprinklers
would not activate. Other concerns relate to the configuration and orientation of heat collectors
over sprinklers. Inspectors have discovered some heat collectors tilted at an angle over the
sprinklers or even installed sideways. The technical concern is that tilted or vertical heat
collectors over sprinklers could obstruct or deflect the spray pattern of the sprinklers (provided
the sprinklers activate), preventing the sprinkler from effectively controlling the fire. Figure 3 of
the attachment shows how an improperly placed heat collector can obstruct the sprinkler spray
pattern.
With respect to the NFPA code requirements, the heat collector concerns raised by NRC
inspectors usually involve one of two issues:
- In fire areas where the licensee commits to NFPA 13, the distance of the sprinkler from
the ceiling does not comply with the NFPA 13 spacing and location requirements (i.e., a
sprinkler with a heat collector below cables installed in cable trays or a midair sprinkler
for transient fire control).
3 The thermal sensitivity of a sprinkler operating element is called the response time index
(RTI). The RTI provides an indication of how fast the element can absorb enough heat from its
surroundings to activate the sprinkler. Standard-response sprinklers have higher RTIs than quick- response sprinklers. The lower the RTI, the faster the sprinkler activates. However, even a quick- response sprinkler with a low RTI will not activate unless it is immersed in the ceiling jet. * Water spray systems have been installed under heat collectors in some fire areas where
the licensee designed the system to the requirements of NFPA 15, Water-Spray Fixed
Systems For Fire Protection. In accordance with NFPA 15, water spray systems
require directional water spray nozzles, which are open nozzles. Open nozzles do not
have a heat-sensitive element (such as a fusible link). This allows water to flow from all
nozzles at the same time to protect the hazard once the detection system receives an
alarm and trips the deluge valve. Since water spray systems typically are open nozzles
(with no heat-sensitive element), there are no NFPA 15 requirements for nozzles to be
located within a certain distance from a ceiling or overhead beam. This is based on the
fact that the principal design consideration for a water spray system, is the spray pattern
the open nozzles will develop in protecting the hazard.
To prevent inadvertent actuation of water spray systems onto components such as
sensitive electrical components, some licensees have installed automatic directional
water spray nozzles, which are closed nozzles. Closed nozzles can only operate when
the heat-sensitive element is activated. So an automatic directional water spray nozzle
operates on the same principle as an automatic sprinkler. They both have heat- sensitive elements which rely on the heat of a fire to fuse (open), to release water on to
the fire. As previously discussed, the closed nozzle and automatic sprinkler both require
proper placement in the ceiling jet so that the heat-sensitive element is exposed to the
convective flow of heat from a fire.
Although NFPA 15 does not require nozzles to be located within a certain distance from
the ceiling or overhead beam, the 2001 Edition of NFPA 15, Section 6.2.1.2 does state
that automatic nozzles shall be permitted when positioned and located so as to provide
satisfactory performance with respect to activation time and distribution. Based on the
operation of the heat-sensitive element, the same concerns with respect to automatic
sprinkler placement and response time are also applicable for automatic directional
water spray nozzles.
The ceiling is widely recognized as a fundamental means of directing heat to the sprinklers
located closest to the fire. The use of sprinklers with heat collectors installed far below the
ceiling has not been demonstrated to be effective and may impair sprinkler system response.
Sprinklers are also used to prevent flashover and the collapse of structural steel. Furthermore, fire areas with large amounts of combustibles above the sprinkler, may not be adequately
protected in accordance with General Design Criterion 3. This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact the technical contacts listed below
or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/ /RA/
Robert C. Pierson, Director William D. Beckner, Program Director
Division of Fuel Cycle Safety Operating Reactor Improvements Program
and Safeguards Division of Regulatory Improvement Programs
Office of Nuclear Material Safety Office of Nuclear Reactor Regulation
and Safeguards
Technical Contacts: Tanya Eaton, NRR Mark Henry Salley, NRR
301-415-3610 301-415-2840
Email: tme@nrc.gov Email: mxs3@nrc.gov
301-415-8111 Email: psl1@nrc.gov
Attachments:
1. Figures 1, 2, and 3
2. List of Recently Issued NRC Information Notices
3. List of Recently Issued NMSS Information Notices This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact the technical contacts listed below
or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
/RA/ /RA/
Robert C. Pierson, Director William D. Beckner, Program Director
Division of Fuel Cycle Safety Operating Reactor Improvements Program
and Safeguards Division of Regulatory Improvement Programs
Office of Nuclear Material Safety Office of Nuclear Reactor Regulation
and Safeguards
Technical Contacts: Tanya Eaton, NRR Mark Henry Salley, NRR
301-415-3610 301-415-2840
Email: tme@nrc.gov Email: mxs3@nrc.gov
301-415-8111 Email: psl1@nrc.gov
Attachments:
1. Figures 1, 2, and 3
2. List of Recently Issued NRC Information Notices
3. List of Recently Issued NMSS Information Notices
DISTRIBUTION:
IN File
- See previous concurrence
DOCUMENT NAME: G:\RORP\OES\Petrone\heatcollector_final.wpd
OFFICE RSE:RORP:DRIP Tech Editor SPLB:DSSA SPLB:DSSA SC:SPLB:DSSA FCSS:FOLB:NMSS
NAME CDPetrone* PKleene* TMEaton* MHSalley* EWWeiss* DMGillen
DATE 06/19/2002 05/24/2002 06/19/2002 06/24/2002 06/25/2002 07/16/2002 OFFICE FCC:FOLB:NMSS BC:SPLB:DSSA D:NMSS:FCSS:FSPB SC:RORP:DRIP PD:RORP:DRIP
NAME PCLee JNHannon RCPierson TReis WDBeckner
DATE 07/15/2002 07/11/2002 07/17/2002 07/19/2002 07/19/2002 OFFICIAL RECORD COPY
References:
1. Fleming, Russell P., High-On Sprinklers, Part II, Sprinkler Quarterly, Spring 1989, pp 21.
2. McCormick, J.W., and DeMonbrun, J.R., Experiments With Sprinkler Head Canopies for
Fire Protection, Oak Ridge Y-12 Plant, U.S. Atomic Energy Commission Y-JA-96 July 2,
1973.
3. NFPA 13, Standard for the Installation of Sprinkler Systems, National Fire Protection
Association, Quincy, Massachusetts.
4. NFPA 15, Water-Spray Fixed Systems for Fire Protection, National Fire Protection
Association, Quincy, Massachusetts.
5. NFPA 231C, Rack Storage of Materials, 1998 edition, National Fire Protection
Association, Quincy, Massachusetts.
6. Shanley, J. H. , and Budnick, E.K., A Study of the Utility of Heat Collectors in Reducing
the Response Time of Automatic Fire Sprinklers located in Production Modules of
Building 707, RFP-4874, Hughes Associates, Inc., January 1990.
Attachment 1 Figure 1 An upright sprinkler with a heat collector
Figure 2 Heat collector with an edge and without an edge
Figure 3 A heat collector obstructing sprinkler spray pattern
Attachment 2 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2002-02, Recent Experience With 07/17/2002 All holders of operating licenses
Supplement 1 Plugged Steam Generator for pressurized-water reactors
Tubes (PWRs), except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-23 Unauthorized Administration of 07/16/2002 All Medical Licensees.
Byproduct Material for Medical
Use
2002-22 Degraded Bearing Surfaces in 06/28/2002 All holders of operating licenses
GM/EMD Emergency Diesel for pressurized- or boiling-water
Generators nuclear power reactors, including
those that have ceased
operations but have fuel on site.
2002-21 Axial Outside-Diameter 06/25/2002 All holders of operating licenses
Cracking Affecting Thermally for pressurized-water reactors
Treated Alloy 600 Steam (PWRs), except those who have
Generator Tubing permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
Note: NRC generic communications may be received in electronic format shortly after they are
issued by subscribing to the NRC listserver as follows:
To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following
command in the message portion:
subscribe gc-nrr firstname lastname
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit
Attachment 3 LIST OF RECENTLY ISSUED
NMSS INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2002-23 Unauthorized Administration of 07/16/2002 All medical licensees.
Byproduct Material for Medical
Use
2002-19 Medical Misadministrations 06/14/2002 All nuclear pharmacies and
Caused By Failure to Properly medical licensees.
Perform Tests on Dose
Calibrators for Beta- and Low- Energy Photon-Emitting
Radionuclides
2002-17 Medical Use of Strontium-90 05/30/2002 All U.S. Nuclear Regulatory
Eye Applicators: New Commission medical licensees
Requirements for Calibration that use strontium-90 (Sr-90) eye
and Decay Correction applicators.
2002-16 Intravascular Brachytherapy 05/01/2002 All Medical Licensees.
Misadministrations
2001-18 Degraded and Failed 12/14/2001 All uranium fuel conversion, Automatic Electronic enrichment and fabrication
Monitoring, Control, Alarming, licenses and certificate holders
Response, and authorized to receive safeguards
Communications Needed for information. Information notice is
Safety and Safeguards not available to the public
because it contains safeguards
information.
Note: NRC generic communications may be received in electronic format shortly after they are issued by
subscribing to the NRC listserver as follows:
To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following command in the
message portion:
subscribe gc-nrr firstname lastname
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit