Information Notice No. 91-79: Deficiencies Found in Thermo-Lag Fire Barrier Installation

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                              December 6, 1991

                               THERMO-LAG FIRE BARRIER MATERIALS


All holders of operating licenses or construction permits for nuclear power 


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees to problems that could result from improperly 
installed THERMO-LAG 330-1 fire barriers that are used to satisfy NRC fire 
protection requirements for safe shutdown components.  It is expected that 
recipients will review the information for applicability to their facilities 
and consider actions, as appropriate, to avoid similar problems.  However, 
suggestions contained in this information notice are not new NRC 
requirements; therefore, no specific action or written response is required.

Description of Circumstances

NRC Information Notice (IN) 91-47, "Failure of THERMO-LAG Fire Barrier 
Material to Pass Fire Endurance Test," reported a number of installation 
deficiencies identified at the River Bend Station (RBS) and discussed a ASTM 
E-119 fire endurance test conducted for Gulf States Utilities (GSU) in 
October 1989 at Southwest Research Institute (SwRI) that ended with a 
failure of a 3-hour THERMO-LAG 330-1 cable tray protective envelope system.  
On August 23, 1991, the vendor, Thermal Science, Incorporated, (TSI), issued 
a letter to a number of licensees that discussed specific installation 
issues raised in IN 91-47 and concluded that the SwRI fire endurance test 
was not a valid test because of deficiencies in the installation of the test 

Other licensees have also identified instances of THERMO-LAG fire barrier 
configurations that were not installed in accordance with the vendor's 
installation procedures manual.  For example, Cleveland Electric 
Illuminating Company (CEI) reported in Licensee Event Report 91-020 that the 
mechanical fasteners (banding straps) on the fire barrier enclosures at 
Perry Nuclear Power Plant had not been installed in accordance with the 
vendor's installation procedures manual.  CEI identified the installation 
discrepancies while conducting routine fire wrap inspections using revised 
inspection criteria.  The licensee 


                                                            IN 91-79 
                                                            December 6, 1991 
                                                            Page 2 of 3 

identified that no fire endurance tests or engineering analysis had been 
performed to support the installed configuration.  The licensees that have 
experienced installation problems have attributed most of the reported 
installation problems to contractor installer errors, incomplete or 
incorrect design documents, and inadequate quality control oversight.  The 
NRC has also identified a number of installation variations as it has 
continued to review the vendor's installation procedures and the 
installation specifications, procedures, and practices for specific plants.  
Some of the installation variations observed by the NRC do not appear to be 
in accordance with the vendor's installation procedures manual and may 
comprise configurations that have not been qualified by fire endurance 
testing or engineering analyses.  In several cases, such as at the River 
Bend Station (RBS) and Washington Nuclear Power Unit 2 (WNP2), the 
installation methods used during initial construction of the plant that 
deviated from the vendor's installation procedures manual were found 
unacceptable when subsequent qualification fire endurance testing resulted 
in fire barrier failures.

On October 17, 1991, the NRC met with TSI to discuss issues regarding 
installation and qualification testing.  The vendor stated that it had not 
included several essential application steps and precautions in its 
installation procedures manual because the information was presented during 
the TSI certification training for installers.  The vendor stressed the 
importance of using skilled and certified craftsmen, and qualified quality 
control inspectors to achieve an adequate fire barrier enclosure.  In 
addition, several licensees have related to the NRC receiving supplementary 
written and verbal installation guidance from TSI representatives that is 
not included in the TSI installation procedures manual.  

The NRC has discussed installation details with licensees, and visited a 
number of sites.  The staff has observed variations among the installation 
procedures and practices regarding the following fabrication details:

-    Methods for sealing and filling joints between panel sections.
-    The orientation and application methods for stress skin.
-    The requirements for raceway support protection.
-    Allowable gap widths between panel sections.
-    The configuration and orientation of structural ribs.
-    Methods for installing vaults and firewalls.
-    Banding material and application methods.
-    Scoring and grooving of panels for fabricating and bending the 
       panels around bends in raceways.
-    Thickness acceptance criteria.

For example, an important task during the installation of THERMO-LAG fire 
barriers is the filling of the joints between adjoining prefabricated panel 
sections with trowel-grade material to the full depth of the panels.  Some 
facilities use a method in which the ends of individual panel sections are 
butt joined to one another and the seam between the panel sections is filled 
and covered with THERMO-LAG trowel grade material (commonly referred to as 
"dry-fitting").  Some licensees fill the joints by "pre-buttering" the edges 
of the individual panel sections with trowel grade material before they join 

                                                            IN 91-79 
                                                            December 6, 1991 
                                                            Page 3 of 3 

panels to ensure that the gap between the panels is completely filled.  The 
vendor did not list this method as an option for installing cable tray 
enclosures in its current installation procedures manual.  However, on 
October 17, 1991, the vendor stated to the NRC that this method was 
acceptable for installing THERMO-LAG panels to cable trays.  In its 
August 23, 1991, letter to licensees, the vendor stated that stress skin 
must be placed over panel joints to ensure a continuous outer layer of 
stress skin for 3-hour barriers and a recent vendor procedure, TSI Technical 
Note 20684-AL, of October 1989, provides updated installation procedures for 
aluminum cable trays and requires that each butt joint be covered by an 
additional layer of stress skin and trowel grade material.  The current 
vendor's generic installation procedures manual does not provide any 
guidance for installing a continuous layer of stress skin.    

The NRC has not been able to verify that all of the specific installation 
variations observed have been qualified by independent qualification testing 
or engineering analyses.  The NRC is continuing to review other technical 
issues regarding THERMO-LAG 330-1 fire barriers, including issues concerning 
the adequacy of qualification testing.  Generic Letter 86-10, 
"Implementation of Fire Protection Requirements," provides additional NRC 
guidance on fire barrier qualification test acceptance criteria and 
evaluation of deviations from tested configurations to substantiate field 

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate Office of 
Nuclear Reactor Regulation (NRR) project manager.

                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical contacts:   Ralph Architzel, NRR
                      (301) 492-0804

                      Loren R. Plisco, NRR
                      (301) 492-1013

                      K. Steven West, NRR
                      (301) 492-1220

Attachment:  List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Wednesday, March 24, 2021