Stray electrical current is a very definite problem and procedures as detailed in O H & S documents have detailed this over a long period.
These types of incidents are real and not just the figment of someone’s imagination and some that come to mind are described below.
The method of overcoming stray electrical currents and gas piping is covered in Australian Standard 5601-2004 (2.11.4) that promotes the use of a metallic bridging device commonly known as a Bonding Strap.
AS 3500.1-2003 also describes the use of Bonding Straps and that they should have an electrical current rating of not less than 70 Amps.
Yesteryear the Gas & Fuel Corporation issued every individual person who was involved with fitting or disconnecting of Gas Meters, pipework and appliances with a set of Bonding Straps or equipment with similar abilities to suit different applications i.e. Cable that had specifically designed ‘G’ clamps to suit large installations or pipe work.
The most commonly known use for using Bonding Straps is when cutting pipework.
Always place one clamp on either side of cut that is to be performed and always work with the Bonding Strap in place even if either side of the cut pipe test safe with a Neon tester or Multi Meter.
Electrical appliances such as Refrigerators, Washing Machines and Dishwasher cycle during their operation therefore voltage (and any fault with these appliances) may not be detected when testing either side of the cut pipe during a dormant period
Bonding Straps should also be used when disconnecting
• an appliance and/or replacing an appliance
• water and gas pipes
• changing a gas control
Incidents investigated have found the house where work may be carried out has no inherent fault with the electrical installation but the fault was traced to the electrical distribution system, (the) residence next door or up the Street and the fault in that residence has travelled through the mains supply of either Water or Gas pipes past other homes to the home where an incident has taken place.
Earthing systems have varied over the years from the once standard application of connecting the earth lead via the metal pipework of a cold water supply.
The introduction of plastic piping systems saw the introduction of an earth electrode commonly referred to as an earth stake.
An earth stake has limitations as to its effectiveness due to the electrical conductivity of the ground it is implanted in; ideally moist ground will provide a better earth
It remains standard practice today that where a cold water metal piping system is in place in a building the earthing system is still connected to both the metallic cold water piping and the earth stake.
Metal pipes for water or gas reticulation in a building were all that was available years ago and as both systems were of a metallic material earthing leads were inadvertently placed on gas reticulation pipework.
Corporation personnel who attended buildings where the earth lead was on gas piping would not work on the installation until an electrician had removed the earth lead and placed it on the cold water piping.
Similarly cold water and gas piping, particularly under a building can be like spaghetti with them laying over each other.
Then and as it is today you are your own Safety Officer it was the determination of the personnel on site if it was safe to work on the site.
Case histories on incidents or near incidents include seeing sparks jumping across from a gas meter to service and fitting lines and in days past from the meter or associated pipework to the metal casing of a meter box. These metal boxes were removed many years ago.
Gas meters and regulator assemblies include non metallic insulating components to restrict a current flow, improper assembly or damaged insulation should be a consideration at all times.
A gas leak in the vicinity of a spark could provide the potential for a much greater consequence.
A gasfitter who was investigating the report of a gas leak at an older house disconnected the fitting line from a gas meter which resulted in a large electrical arc flashing across between the meter and the fitting line.
Investigation initially revealed that part of the fitting line became electrically alive at a reading of 200VAC. To make matters worse the earth wire that originates from the neutral bar at the electrical switchboard (meter) was not connected to the metallic cold water piping, this meant the earth wire was flapping in the breeze and had the potential to be at 240VAC.
The ultimate cause was found to be a break in the neutral supply at the connection of the electrical supply to the facia board of the house.
Electricity is supplied via an active wire and will return to its original source of supply via the neutral wire.
As in this case if the neutral wire is broken electricity will follow the least line of resistance to earth. Remembering the earth wire was disconnected from the water supply we still have interconnection of both the water supply and the gas supply via the storage hot water service on the property let alone the contact been made where supply pipes were laying over each other.
Yes the gasfitter could have been killed or badly hurt as he did not employ the use of a Bonding Strap his saving grace was when he disconnected the fitting line it fell away only brushing the back of his hand.
Another instance was when a fitter was going to change over a gas meter, he had a young apprentice with him just out of the training school, and they gathered all the necessary equipment to do the work less the Bonding Strap.
The apprentice realised this and with the recent safety training he had experienced at school offered to return to the work van and obtain the Bonding Strap; the fitter said it would be okay, but if he wanted get the Bonding Strap.
Both the fitter and the apprentice went in opposite directions and when the apprentice arrived with the Bonding Strap at the meter location there were some tools laying around but no fitter.
Only when some moans and groans were heard some twenty feet away from some bushes the fitter was found doubled over sitting on his knees with both arms wrapped around his stomach did he say “what was that you said”?
One last experience which proves no one can foresee hidden dangers was about the guy who owned a very aggressive and very savage American Pit Bull terrier who decided to relieve himself on the gas meter, changed the dog’s whole demeanour after the incident.