The objective of this project was to determine if ignition of gas can occur during the use of vacuum excavation equipment near leaking natural gas lines and/or during the removal of water from gas mains. Vacuum excavation has been used by the gas distribution industry for several decades without incident.
Summary:
The objective of this project was to determine if ignition of gas can occur during the use of vacuum excavation equipment near leaking natural gas lines and/or during the removal of water from gas mains. Vacuum excavation has been used by the gas distribution industry for several decades without incident. Some of the more popular hoses used in vacuum work, such as polyethylene drain tile hose purchased at home building supply stores, are favored because they are inexpensive and light. They are also good at creating static electricity. Experiments demonstrated that situations can exist with high static voltages and flammable mixtures of gas and air in the hose and vacuum chambers, without ignition. Several reasons were identified why it is difficult to create an ignition in the use of vacuum equipment with a non-conductive (static generating) hose, including: the high flow rates of large quantities of air usually keep gas concentrations below the lower flammability limit; and the combination of dirt and water entrained into the air stream can provide a thermal mass sufficient to inhibit and even quench combustion. A high-energy spark can cause ignition and an explosion. An automotive spark plug was used to create ignition in a flammable mixture being drawn into the hose. Ignition occurred in the hose, blowing part of it apart; however, no combustion occurred in the vacuum truck itself. This research concludes that vacuum excavation can be used safely if proper precautions are taken.
