Resolution No. 4814 - Laserfiche WebLink

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standards, maintenance and testing requirements. For the United States as a whole, a network of about 300,000 miles of natural gas transmission ~ines serve about 1.5 million miles of distribution system lines which serve about160 million customers. Overall the safety record of natural gas transmission pipelines is good with relatively few significant accidents. The Eugene/Springfield Metro Area also has a natural gas distribution system within Eugene and Springfield operated by Northwest Natural Gas. The natural gas pipeline systems of local gas utilities, including the systems in the Eugene/Springfield Metro Area, almost always follow road and street patterns because of established utility rights of way and because of the need to connect with each building served. Thus, for areas served by natural gas, the local street network is essentially identical to the natural gas distribution pipe network. Overall, the safety record of natural gas distribution pipelines is good with relatively few significant accidents. Natural gas is not toxic (i.e., not poisonous). However, natural gas can be an asphyxiant if it displaces oxygen in an enclosed space. Natural gas burns readily when ignited, but only when gas concentrations are between 4% and 15% in air. In its pure state, natural gas is both colorless and odorless. The strong odor normally associated with natural gas is an odorant deliberately introduced at Iow concentrations to serve as a warning of the presence of natural gas. The strong odorant is generally added to natural gas at the local distribution level, by local gas utilities. Fires and/or explosions from natural gas leaks in pipelines are rare. In part, the rarity of fires and/or explosions is due to the fact that natural gas is about 1/3rd less dense than ordinary air. Thus, leaking natural gas does not accumulate near the ground or "pond" in Iow-lying areas (as heavier gases such as liquefied natural gas or gasoline fumes may do). Instead, leaking natural gas rises rapidly and is dissipated by dilution in the atmosphere. The fires and/or explosions that do occur from natural gas leaks are generally in buildings where the confined space allows leaking gas to accumulate until ignited. In 2000, annual statistics of hazardous materials incidents5, prepared by the Office of State Fire Marshal, show only 45 natural gas incidents statewide in Oregon. Pipeline breaks due to natural causes may occur due to landslides or earthquakes. Earthquake induced pipe breaks for natural gas transmission lines are most likely to occur in areas of soft soils subject to liquefaction and/or lateral spreading which cause significant pipe displacements. The most likely locations for such breaks during an earthquake are on slopes of soft ground near where pipelines cross rivers or streams. The most common human-related cause of pipeline breaks is pipeline rupture due to pipes breaking when heavy construction equipment is used to excavate for construction projects. Most such breaks occur in local distribution lines. For major transmission lines, breaks are possible, but much less common, because of the robustness of the transmission pipelines and because the major transmission lines are generally well marked with frequent warning signs. Major pipeline breaks could disrupt gas service over wide areas with resulting significant economic impacts. Pipeline breaks can also be caused by deliberate actions of sabotage or terrorism. Although Public Review Draft: October 12, 2004 14-11