Fire Risks Involving Corrugated Stainless Steel Tubing (CSST) Gas Lines and Lightning Strikes
The 1988 commercial introduction of corrugated stainless steel tubing (CSST) to distribute natural and LP gas within and throughout residential and commercial buildings was welcomed by the gas industry as a cost-effective means to deliver their product to consumers. Corrugated stainless steel tubing (CSST) is a cost-effective alternative to standard threaded black-iron gas piping for residential, commercial and industrial applications. It's light-weight, flexible, and requires fewer connections and fittings, which make it easier to install than black-iron piping. These factors add up to substantial labor savings for installers and cost savings for property owners.
Corrugated stainless steel gas tubing (CSST) consists of a continuous, flexible, stainless steel pipe with an exterior PVC covering. It is usually installed utilizing a central manifold configuration with "home runs" to gas appliances. Due to its construction, it is easily routed around obstacles and requires fewer connections than traditional gas piping.
To date, over 150 million feet of corrugated stainless steel tubing has been installed in roughly 2 million homes.
Research sponsored by the Gas Research Institute from 1983 to 1989 was used to in the creation of a nationally recognized standard for CSST systems. The initial standard was developed by the American Gas Association Laboratories in 1986, but was considered only a bench standard. It was eventually designated as AGA 1-87. This standard ultimately became an ANSI standard in 1991 which was known as ANSI/AGA LC-1-1991 “Interior Fuel Gas Piping System Using Corrugated Stainless Steel Tubing.” Since that time, updating and improvements have been made to this standard, such that it is currently known as ANSI LC 1-2005/CSA 6.26-2005 “Fuel Gas Piping Systems Using Corrugated Stainless Steel Tubing (CSST).” All commercially available CSST systems are certified to the list of requirements included in this standard.
All CSST manufacturers are required to publish a Design and Installation Guide that complies with the ANSI Standard. Included within this standard is the requirement to address electrical bonding and grounding. Furthermore, because of cooperation within the industry, essentially all of the design and installation guidelines are identical between all six manufacturers which is a critical point affecting the bonding of CSST systems.
Corrugated stainless steel piping eliminates the need for installing black iron pipe. Because of its flexibility, it can be pulled through wall and ceiling cavities in a manner similar to electrical wire. Due to the reduction in fittings, the potential for leakage is substantially reduced. Stainless steel gas tubing is easy to expand and to use in retrofits where frequent bends and turns are necessary. CSST is rated for high pressure and if it is used at higher pressure, the pipe size, and therefore material cost, can be reduced. Typically the cost to install CSST is less than that of standard black iron due to the reduction in labor costs. Even though the material costs of the fittings and tubing is higher, approximately half of the total costs is labor. However, in some instances the cost may be higher where multiple appliances are located next to one another.
CSST is installed using special fittings and cutting tools developed and approved by the manufacturers. Connections can be made quickly with the proper tools. Due to its thin-walled construction, striker plates must be installed where the gas lines penetrate wall studs to protect lines from puncture during drywall installation similar to the ones installed over water lines. Installation of a CSST system for a single-family home can be completed in less than a day. Currently CSST is not rated for underground use and should not come in contact with the ground.
Some installation tips:
• The manufacturer’s installation instructions and flexible gas tubing design should be on-site for inspections.
• The installation of CSST should be at least 6 inches above grade and limited to the interior of buildings.
• Installation of CSST should only be performed by trained technicians that have been certified by the manufacturer and the technician should be present during inspection of the installation and present their current certification card.
• All gas piping within the building that utilizes CSST should be permanently identified by a metal tag which names the CSST manufacturer that should be attached to the gas meter outlet.
• Only one CSST manufacturer’s product should be used in a system within a building. Intermixing of CSST systems is not acceptable due to the proprietary design of fittings and specific sizing criteria.
Lightning Related Issues
Lightning strikes the United States more than 25 million times each year and according to Underwriters Laboratories (UL), lightning accounts for more than $1 billion in annual structural damage. A single bolt of lightning can carry over 100 million volts of electricity, and in reality, there are no construction methods or safety measures that can completely protect a structure from a direct lightning strike. CSST gas pipe, however, is susceptible to damage from non-direct lightning strikes as well.
Lightning is one of the most destructive forces on the planet and can cause serious damage to whatever material it comes in contact with. Direct and indirect strikes on or near structures can cause severe damage to buildings and cause fires that can result in the loss of property and lives. In spite of this, and with a few exceptions, municipalities throughout the United States do not require the installation of lightning protection systems. Typical electrical grounding systems are required to address the issue of lessening the severity of the lightning energy. However, the electrical grounding system is only designed to protect the building occupants from ground-faults and not from lightning strikes. This is the reason that many systems such as electrical wiring, coax cable, metallic piping, ducting, and appliances either fail or are damaged during electrical storms.
Since the PVC coating on the tubing does not provide sufficient insulating properties to prevent the creation of an arc between the stainless steel tubing and some other bonded metallic building component, a fire can be started by way of the arc burning a hole in the tubing wall and gas exiting the tubing while in the presence of the arc.
Stainless steel has a fairly high melting point, so if a hole is found in CSST, the hole was most likely caused by lightning. Lightning activity is tracked when available through various sources, including Strike Fax reports. Remember that the lightning strike does not need to be a direct hit to the structure since strikes that are several miles away can still potentially cause CSST failures.
– Fire claims which are related to CSST failure have significant subrogation potential. However, this potential may be limited by the class-action settlement with four CSST manufacturers. It also may be limited by new developments in research regarding CSST, which may indicate that the new bonding requirements may not be sufficient to protect the CSST from sustaining a breach during a lightning event.
A hole caused by a simulated lightning strike
The National Electric Code (NEC), Section 250.104b, states that “bonding all piping and metal air ducts within the premises will provide additional safety”. Gastite recommends that all continuous metallic systems be bonded and grounded. The owner should confirm with an electrical or construction specialist that each continuous metallic system in a structure has been bonded and grounded by an electrical professional in accordance with local building codes. This should include, but is not limited to metallic chimney liners, metallic appliance vents, metallic ducting and piping, electrical cables, and structural steel.
The NEC provides extensive coverage on the subject of grounding and bonding in Section 250 of the Code. There are three basic reasons for grounding:
• To limit voltages caused by lightning or by accidental contact of the supply conductors with conductors of higher voltage
• To stabilize the voltage under normal operating conditions
• To facilitate the operation of over-current devices (such as fuses, circuit breakers or relays) under ground-fault conditions
Bonding is the permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to safely conduct any current likely to be imposed. The purpose of bonding is to establish an effective path for fault current that facilitates the operation of the over-current protection device.
To simplify the Code, only the electrical system is grounded for residential applications. The electrical system is grounded to earth through grounding electrodes, typically a rod, pipe or plate. However, there are other means to ground the electrical system, including the use of the reinforcing steel in the foundation. All other electrically continuous, metallic pathways (such as water pipe (if copper), coax cable and gas piping) are bonded to this grounding system. Bonding of gas piping, in particular, is installed in accordance with Section 250.104 (B):
(B) Other Metal Piping. Where installed in or attached to a building or structure, metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.
FPN: Bonding all piping and metal air ducts within the premises will provide additional safety.
Referring to Section 250.122 (Size of Equipment Grounding Conductors), Table 250.122 provides guidance for sizing the bonding jumper for the gas piping system:
(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122 but shall not be required to be larger than the circuit conductors supplying the equipment.
Table 250.122: Minimum Size Equipment Grounding Conductors for Grounding Raceways and Equipment:
15 AMP 14 AWG Copper
20 AMP 12 AWG Copper
30/40/60 AMP 10 AWG Copper
100 AMP 8 AWG Copper
200 AMP 6 AWG Copper
CSST should not be installed within a chase or enclosure that houses a metallic chimney liner or appliance vent that protrudes through the roof. In the event such an installation is necessary and conforms to local building codes, the metallic chimney liner or vent must be bonded and grounded by a qualified electrical professional, and a separation distance, as specifically permitted by the applicable local building code between the CSST and the metallic chimney liner or vent, is required. Physical contact between CSST and the metallic chimney liner and/or vent is prohibited.
Since nearly half of all new homes contain CSST, homeowners and new homebuyers should be aware of the concerns and have a qualified home inspector verify that the bonding of all metallic components were properly done.
NFPA 54 - National Fuel Gas Code
Corrugated stainless steel is more vulnerable to arcing damage than other gas piping materials because of its thinner wall thickness. NFPA 54 was revised in the 2009 edition to address this, based on a number of incidents that became apparent after a class action lawsuit was settled. Section 7.13, Electrical Bonding and Grounding, has been revised to require that all CSST systems be bonded to the electrical service ground where the gas service enters the building using at least a 6 AWG copper conductor or equivalent. NFPA 54 requires that CSST be installed in accordance with the manufacturer’s installation instructions in 7.2.8.
Areas with high lightning risk include but are not limited to:
Most manufacturers use a thin yellow PVC jacket for the coating on the CSST. However, one manufacturer (Omegaflex) has developed a CSST product called CounterStrike™ that is specifically designed to dissipate the energy from an arc from another energized metallic system. The standard yellow coating is replaced with a thicker proprietary black jacket material designed to dissipate energy along its length. Omegaflex claims that the CounterStrike™ product inhibits lightning energy from concentrating at any point along the gas line and spreads out the energy over a larger area. This feature minimizes the possibility of a breach of the tubing wall when the CSST is struck by an arc.
Even with the modifications to the bonding requirements and new manufacturing variations, some local and state code officials feel compelled to review the new ANSI standard and may reject the recommendations stated within the standard.
Some manufacturers warrant their CSST and fitting for a period of one year after installation.
There have been reports of fires caused by lightning strikes near homes with CSST flexible gas piping. The cause of these fires has been attributed to either a lack of or inadequate bonding of the CSST, which resulted in arcing damage to the tubing. A class action law suit involving four CSST manufacturers: Omegaflex (TRACPIPE or COUNTERSTRIKE); Parker-Hannifin Corp. (PARFLEX); Titeflex Corp. (GASTITE); and Wward Manufacturing, Inc. (WARDFLEX). The parties to the suit have signed a Settlement Agreement that provides class members with a partial to full financial reimbursement for either a lightning protection system or upgraded bonding of their existing CSST system. For further information on the Settlement Agreement, visit www.CSSTsettlement.com; call the Administrator at 1-800-420-2916; or write to the CSST Settlement Administrator at P.O. Box 4349, Portland, OR 97208-4349.
Although only four of the six CSST manufacturers were parties to the Class Action suit, all six have informally agreed to upgrade their bonding requirements for the CSST system. The new bonding method requires the attachment of a bonding clamp to either the CSST fitting or to a piece of steel pipe located near the service entrance to the building. The bonding jumper shall be no smaller than a 6 AWG copper wire for residential applications. Although the final bonding solution is essentially the same for all six manufacturers, the six technical pronouncements appear to be different.
A bonding clamp connected to the steel gas line near CSST connection fitting
Confusion arises with the requirement to size the bonding jumper in accordance with Table 250.66. This table is intended for the sizing of the grounding electrode conductor which is not the same as the bonding jumper. The grounding electrode conductor is based on the size of the ungrounded service conductor at the entrance of the building. This can result in a bonding jumper much larger than a 6 AWG copper wire especially for large buildings and/or multi-family structures. Using the exception in Section 250.66(A), if a rod, plate, or pipe is used as the grounding electrode, the grounding electrode conductor need not be larger than a 6 AWG copper wire. The argument may still need to be made that the bonding jumper be sized in a similar fashion. This exception is open to interpretation and can be misused when sizing the bonding jumper and caution is recommended when referring to this particular section of the NEC.
The CSST must be bonded only at the end nearest the entry of the gas service into the building. If it is bonded at both ends, or at the end nearest the gas-burning appliance, the CSST may carry stray electrical currents or act as a grounding conductor, which can damage the CSST and its fittings, and cause leaks.
Corrugated Stainless Steel Tubing for Fuel Gas Distribution in Buildings and Concerns over Lightning Strikes (The NAHB Research Center, Inc.)
Ward Manufacturing http://www.wardmfg.com/
Parker Hannifin Corporationhttp://www.parker.com/parflexsystem/
Tru-Flex Metal Hose http://www.tru-flex.com/
Mechanical, lightning groups at odds over CSST
Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter and individuals should utilize a licensed professional in determining the appropriate specifications that pertain to their project.