238
GLOSSARY
capacity, and must be set to operate, to insure, the pressure may not cause the unsafe operation of any connected and properly adjusted gas utiliza- tion equipment.
Line Section. A continuous run of pipe between adjacent pressure pump stations, between a pres- sure pump station and terminal or breakout tanks, between a pressure pump station and a block valve, or between adjacent block valves.
Local DistributionCompany (LDC). Local distri- bution companies typically transport natural gas from delivery points located on interstate and intrastate pipelines to households and businesses through thousands of miles of small-diameter distribution pipe.
Local Emergency Planning Committee (LEPC). A committee appointed by a State Emergency Response Commission, as required by SARA Title III, to formulate a comprehensive emer- gency plan for its region.
Lower Explosive Limit (LEL). The lowest con- centration at which a gas or vapor is flammable or explosive at ambient conditions.
M
Magnetic Flux Leakage (MFL). A magnetic method of nondestructive testing that is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. The basic principle is that a powerful magnet is used to magnetize the steel. At areas where there is corrosion or missing metal, the magnetic field “leaks” from the steel. In an MFL tool, a magnet- ic detector is placed between the poles of the magnet to detect the leakage field. Analysts inter- pret the chart recording of the leakage field to identify damaged areas and hopefully to esti- mate the depth of metal loss.
Main Distribution Valves. Valves on a natural gas distribution system, normally located in the street, that control large sections of the main gas grid.
Main Line Valve (MLV). Installed along the nat- ural gas transmission pipeline system to help isolate or control the flow of the gas. They are generally installed approximately 10 to 20 miles along the pipeline and are used to isolate a par- ticular section of the pipeline. May also be referred to as Gate Settings.
Material Safety Data Sheet (MSDS). A docu- ment which contains information regarding the chemical composition, physical and chemical properties, health and safety hazards, emergency response, and waste disposal of the material as required by 29 CFR 1910.1200.
Maxium Operating Pressure. The maximum pressure at which a pipeline or segment of a pipeline may be normally operated under this part.
Meters.A commonly used general term for mon- itoring and detection instruments used to detect the presence and/or concentration of contami- nants within an environment.
Methyl Tertiary Butyl Ether (MTBE). A chemical compound with molecular formula C5H12O. MTBE is a volatile, flammable and colorless liq- uid that is immiscible with water. MTBE is a gasoline additive, used as an oxygenate and to raise the octane number. Its use has declined in the United States in response to environmental and health concerns.
Microbiologically Influenced Corrosion. Pipe- line corrosion resulting from microbes that pro- duce corrosive conditions.
Minerals Management Services (MMS). De- partment of Interior agency responsible for off- shore, non-transportation-related facilities locat- ed seaward of the coastline, including certain pipelines.
Miscible. Refers to the tendency or ability of two or more liquids to form a uniform blend or to dis- solve in each other. Liquids may be totally misci- ble, partially miscible, or non-miscible.
Mitigation. Any offensive or defensive action to contain, control, reduce, or eliminate the harmful effects of a hazardous materials release.
Monitoring. The act of systematically checking to determine contaminant levels and atmospher- ic conditions.
Monitoring Instruments. Monitoring and detection instruments used to detect the pres- ence and/or concentration of contaminants within an environment. They include: Combus- tible Gas Indicators (CGI), Oxygen Monitors, Colorimetric Indicator Tubes, Specific Chemical Monitors, Flame Ionization Detectors (FID), Gas
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