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| Installation of a fiber optic communications cable in a natural gas line |
Description of Problem
The use of laser and other optical beam equipment in gassy and dusty atmospheres was generally thought to be safe. For example, laser-based level monitors are used in coal storage facilities. Laser-guiding fiber-optic cables for telecommunications have been installed inside natural gas pipelines in several states. Guidelines were needed to define if and when a laser beam can be considered a potential ignition source in such environments.
Research and Development Activities
Research to determine the risk of laser-based optical equipment igniting a flammable atmosphere was done to support the development of national and international laser safety standards. Continuous-wave, diode-array lasers and fiber lasers were used to measure the dimensions and durations of the laser beams needed to ignite flammable gas atmospheres and dust clouds. Atmospheres containing methane, propane, and butane were tested. Iron oxide was deposited on the end of a fiber to simulate a broken fiber in a dirty environment. Lean mixtures of methane ignited at 410 mW, rich mixtures of butane at 300 mW, and rich mixtures of propane at 250 mW. Two types of coal dust clouds were also tested. The significant findings were that Pittsburgh seam coal and Powder River Basin coal both ignited using 2 W out of a beam diameter of 0.2 mm. Corn starch, an easily ignitable grain dust, was also tested and found to ignite using 1.5 W out of a 0.2-mm-diam fiber.
R&D Outputs and Transfer Activities
NIOSH research helped form the basis of the American National Standards Institute (ANSI) and International Electrotechnical Commission (IEC) documents on laser safety in flammable atmospheres. Research results were published in two technical articles. A U.S. patent , "Method and Apparatus for Safety Testing Optical Systems for Hazardous Locations," was awarded on December 23, 2003.
Description of Intermediate Outcome
ANSI cited NIOSH research results in its technical report (ANSI/ISA-TR12.21.01-2004) on fiber optics used in flammable environments. The report also credits NIOSH as the lead developer of the document. It was used as the base document for an IEC standard, which is in the "committee draft for vote" stage. The draft document, IEC 60079-28 Ed. 1.0: "Protection of Equipment and Transmission Systems Using Optical Radiation," also cites NIOSH research. In addition, the Mine Safety and Health Administration published a notice of intent to review parts of the IEC 60079 standard for application to U.S. mining equipment approvals. Safety recommendations called out by the ANSI technical report are cited in a draft American Society for Testing and Materials International Standard WK2307, "Standard Specification for Selection of Fiber-optic Cable and System Components for Use in Natural Gas Pipelines." Collectively, these standards help ensure that laser applications can be installed safely in mines and other flammable environments.