Evaluating the Potential for “Victim” Holes Not Caused By Lightning in CSST

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Expertise Includes:

    • Electrical & Mechanical Control Systems
    • Fires & Explosions
    • Gas Fired Equipment & Appliances
    • ICC, NFPA, OSHA Codes & Standards
    • Industrial Processes & Operations

Prior to becoming a forensic engineer, I spent many years in industry designing fuel gas fired equipment. This included designing gas grills, commercial cooking appliances, and large industrial systems.  I learned a lot about the safe use of natural gas and propane. Once I entered the forensic engineering field, that experience helped me in evaluating fires involving natural gas and propane equipment and piping systems. One such area that I have found particularly interesting are fires involving Corrugated Stainless Steel Tubing (CSST).

CSST is a material used to plumb fuel gas inside structures.  It is used as an alternative to traditional black steel pipe or copper tubing. The stainless steel tube of CSST, in certain circumstances, will perforate when subjected to electrical arcing, including that due to local lightning strikes.  The escaping fuel gas from these perforations has obvious implications as to causing fires.

Figure 1: Burning natural gas escaping from a hole in a section of CSST.

Figure 1:  Burning natural gas escaping from a hole in a section of CSST.

Any fires that potentially involve CSST should be carefully examined by investigators familiar with CSST and its installation requirements. Installation requirements are given in the specific manufacturer’s installation instructions and in NFPA 54, National Fuel Gas Code and in the International Fuel Gas Code.   Interestingly, these installation requirements have undergone considerable changes in the last few years.

CSST fire investigations may lead to litigation over alleged defects in the CSST product and its installation. In some cases,  it is alleged that holes found in CSST post fire investigations were actually caused by contact between CSST and energized electrical conductors under exposure from the fire.  In this scenario, the holes could be considered “victim” holes and not causative in starting the fire.  I was involved in a litigated CSST loss in which that assertion was made by an expert for the CSST manufacturer. I felt that the expert’s experimental work supporting his assertion was less than robust, therefore I decided that some alternative experimental work was in order to help determine if some CSST failures could be explained by this fire “victim” scenario.

The testing that I, and Keith Atkinson, CFEI, conducted, subjected energized non-metallic (NM) cable, in close contact with grounded CSST, to fire conditions.  Multiple tests were run until either the overcurrent protection device (circuit breaker) opened or a hole was arced in the CSST, or both.   These tests placed the CSST and NM cables in various arrangements, consistent with those that might occur in actual construction.

Figure 2:  One of twelve tests where a junction of LP gas charged CSST and 5 sections of energized NM cable were subjected to fire conditions.

Figure 2: One of twelve tests where a junction of LP gas charged CSST and 5 sections of energized NM cable were subjected to fire conditions.

The testing indicated that it is possible to create arced holes in CSST by exposure to energized conductors in fire conditions. Of the 60 strands of NM cable that we exposed to fire conditions, 19 of those conductors arced to, and created holes in, the CSST.  The testing also examined the morphology of the holes and conductors including SEM/EDS analysis.  Observations of the stability of flames burning at the resulting gas jets were also made.  These observations maybe helpful in determining the cause of holes found in CSST on fire scenes.

The experimentation work we performed was used as the basis of a technical paper: Analysis of the Potential for Perforation of Corrugated Stainless Steel Tube (CSST) by Energized Branch Circuits in Fire Conditions.  This paper was peer reviewed and accepted for presentation at the 2014 International Symposium on Fire Investigation Science & Technology.  A link to the paper is included.

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CSST Testing with John Holecek

John Holecek, senior consulting engineer at Warren, is a licensed professional engineer in South Carolina, North Carolina, Alabama, Florida, Georgia, Ohio and Virginia and has both a Bachelor of Science in Mechanical Engineering and Master of Science in Mechanical Engineering from the University of South Carolina. A certified fire and explosion investigator by the National Association of Fire Investigators, John has more than 22 years experience in the design of industrial process equipment and is extremely knowledgeable in ICC, NFPA and OSHA codes and standards. He pairs more than 13 years of experience supervising manufacturing operations with deep knowledge in areas such as applied industrial heat transfer in oven design, industrial electrical process and motor control systems, material handling systems and fire protection systems. In addition he’s designed paint finishing systems, and commercial and consumer gas fired cooking appliances. John, who has more than 22 years’ experience managing outside contractors in site safety requirements and installation of industrial process equipment, is well versed in federal and state worker safety and environmental regulations.

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