CSST and Lightning

According to the National Lightning Safety Institute, each part of the country experiences a different rate of lightning strike occurrences, known as the “flash density rate.” Below is a map from the National Lightning Detection Network showing a five year average of lightning density across the United States. The red areas are the highest density areas, and the grey areas are the lowest density areas. But any locale can experience lightning anytime if certain conditions prevail.





According to the National Fire Protection Association, there are on average about 370,000 fires to residential buildings in the United States every year.  See the chart.  Most fires are caused by cooking equipment, heating equipment, electrical equipment, etc.  Other causes of residential fires include playing with heat source (7,400 fires every year), and lightning (about 4,300 fires/year or about 1% of the total).  One small subset of lightning fires are lightning fires where natural gas or propane was the material first ignited – those account for about 160 fires every year.  Some of those fires involve CSST, but not all of them because these types of fires were reported before CSST was introduced in the United States.  So if we assume that one-half of those 160 fires involved CSST, it’s about 80 fires per year.  While those fires are a serious issue, it is plain that CSST fires caused by lightning are not a significant fire threat in the




Another way to look at the data is to determine if there is a correlation between the rate of residential lightning fires and the growth of CSST in the United States.  See the chart.  As you can see, the growth of CSST in the United States has been dramatic – especially in the boom years between 2002 and 2006.  At the same time, the rate of residential lightning fires in the United States has decreased from 60 per million homes in the early 1990s to about 30 per million homes around 2011.  The trend lines are pretty clear that the increased use of CSST in the United States has not caused an increase in residential lightning fires; in fact there was a decrease in residential lightning fires during the period of wide-spread use of CSST in the United States.

Although the data does not include years after 2011, the rate of CSST installed in the United States has continued to rise, so that cumulative at the end of 2015 there was over 1 billion feet of CSST installed in the United States.

Fire Safety Line Chart


According to insurance industry sources, there were about 99,000 claims involving lightning damage to property in 2015, which was down from the five year average of 130,000 and the high of 278,000 in 2003.  Most of the claims are for damage to personal property, such as electronic appliances like flat screen TVs and computers.  However, there are, on average, 4,300 lightning fires to residences in the United States each year, so the chances of a lightning fire are very low even if lightning has impacted the house.

It is common for lightning to exceed 100,000 volts and 30,000 or more amps. The current induced by a lightning strike does NOT “take the path of least resistance” as popularly believed. Current from lightning takes ALL paths to ground.

Lightning can cause significant damage directly, by striking the building, or indirectly, by electrical currents igniting structural parts or systems within the house, which could cause further damage.

Once the lightning energy is inside a building, it will seek to return to ground along every possible path. In that process, the energy may jump—or arc—from one pathway to another, depending on the electrical resistance of the material.  An electrical arc is a high-temperature flash though the air from a pathway having a higher electrical potential to a pathway have less electrical potential.  Arcing is very likely to cause damage to mechanical and electric systems.

Buildings Line Chart

See what happens when lightning strikes. Click this link to see what happens to a house hit by lightning.


Buildings Diagram


Electrical wiring is often damaged by lightning. Due to its low insulation value (600 volts), common household wiring can be easily breached by arcs caused by high lightning voltages. Once the insulation is damaged by that arcing, it is possible for electrical wiring to cause fires by further arcing of the household current, or contact with flammable materials that are close to the damaged wiring.

Similarly, gas piping systems convey flammable gas fuel that may add to the fire hazard if any system components—including valves, regulators, and appliance connectors—are damaged. However, this is not a recent phenomenon. Black iron piping systems using schedule 40 pipe can be compromised by lightning strikes.  Here is a report of black iron pipe being damaged from lightning.  Leaking of fuel gas from a gas piping system (whether from steel, copper, or CSST) damaged by lightning can cause a fire or an explosion.


All metallic electrical and mechanical systems, including all forms of gas piping, are vulnerable to lightning energy that enters a building during a strike. When lightning strikes a building or near a building, the metal systems inside the house – the building’s pipes, wiring, and other metallic systems – will have different electrical potentials.  If two metallic systems such as piping, wiring, coaxial cable, or metal ducts have greatly different electric potentials, an arc can form between them.

For this reason, metallic gas piping must be connected or “bonded” to an earth ground.  The bond is simply a bare copper wire that runs from the gas piping to the building’s ground.  This is now a requirement for all CSST systems.  The National Fuel Gas Code (NFPA 54: Section 7.13.2) states: “CSST gas piping systems shall be bonded to the electrical service grounding electrode system at the point where the gas service enters the building. The bonding jumper shall not be smaller than 6 AWG copper wire or equivalent.”

Bonding enables the potential of all piping and appliances connected to the electrical service to rise and fall equally. Where potential is equal, arcing is less likely to occur. When a CSST system is properly bonded to the electrical service, it helps reduce the difference in the electric potentials of two circuits, reducing the risk of arcing between them.

The CSST industry worked with the National Fire Protection Association and the National Fire Research Foundation in a comprehensive study that conclusively showed that bonding of the CSST gas piping system will prevent electrical arcing caused by lighting.

The CSST industry has advocated for the mandatory requirement for bonding all gas piping since 2008, and has worked with numerous advocacy groups, including the National Association State Fire Marshals, and the national propane group, to alert contractors, builders and home owners to have their CSST system bonded.  However, as you can see below, the national building codes do not uniformly make this requirement clear and conspicuous in the building codes.


Currently, with regard to CSST, there is a conflict between the National Fuel Gas Code and the National Electrical Code.

National Fuel Gas Code (2015)

“CSST gas piping systems, and gas piping systems containing one or more segments of CSST, shall be bonded to the electrical service grounding electrode system, or where provided, lightning protection electrode system.” (7.13.2)  In addition, the bonding jumper (a) must connect to a metal pipe or CSST fitting, (2) be no smaller than 6 AWG, (3) cannot be longer than 75’, (4) be connected to the electrical ground in accordance with the NEC, and (5) use a clamp device listed to UL 467.

National Electrical Code (2014)

If installed in, or attached to, a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to any of the following:

  1. Equipment grounding conductor for the circuit that is likely to energize the piping system
  2. Service equipment enclosure;
  3. Grounded conductor at the service;
  4. Grounding electrode conductor, if of sufficient size;
  5. One or more grounding electrodes used.

The bonding conductor(s) or 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). (250.104(B))

The NEC does include Informational Notes on this section that state that (1) “Bonding all piping and metal air dcts within the premises will provide additional safety,” and (2) “Additional Information for gas piping systems can be found in Section 7.13 of NFPA 54, National Fuel Gas Code.”

While the NFGC requires a minimum of a 6 AWG copper wire to bond CSST to the electrical ground, the NEC would allow a wire sized to handle the circuit that could energize the piping—that is the appliance rating. Furthermore, the NEC allows the use of the equipment grounding conductor (the bare copper grounding wire) to serve as the bond. In most cases, those wires will be smaller than 6 AWG—usually 14 AWG. While that size wire may be adequate for household current, it will not be sufficient to handle overvoltage situations such as transformer failures or lightning. That is why the CSST manufacturers lobbied for a change to the national codes to require bonding of all metal gas piping systems. This was partially successful at the NFGC, and work is continuing to bring the NEC toward that position. It is worth noting that a footnote to NEC 250.104(B) states that bonding provides additional safety.


In Canada and Europe, the building codes require that all metal systems in the home must be bonded to the grounding electrode.  This is called “equipotential” bonding.  If the house is struck by lightning, then the electrical potential of all metal systems in the house will rise and fall at substantially the same rate as the lightning energy seeks a path to ground.  Because there is no significant difference in electrical potential between different metal systems, there is no arcing of electricity, and no damage to the building systems.

There have been no recorded incidents of lightning damage to CSST from lightning in Canada or Europe.  This proves that the problem is not with the product itself, but rather with the building codes that do not address the lightning threat.


Unfortunately, because of the confusion and conflicts in the building codes, and because plumbers install the gas piping and electricians install the bonding wire, there is no simple clear cut direction to put a bonding wire on the gas piping, including the CSST.  This leads to uneven application and enforcement of the bonding rule.  That is one reason why new technologies have been developed to address the electrical arcing issue caused by unbonded gas piping systems.  That CSST technology greatly reduces the risks of arcing by using an energy-dissipating jacket that is applied over CSST piping.  The energy-dissipating jacket spreads energy over a wide area, decreasing the likelihood of electricity forming a focused arc on the CSST. The energy dissipating properties improve the CSST’s ability to withstand damage due to arcing. The jacket also reduces the level of energy as it moves downstream, minimizing risks to regulators, appliance connectors, and other mechanical systems, all of which could contribute to the potential for fire.