Dangers of natural gas pipe purging into buildings

Cherie Berry, Commissioner of Labor 1-800-625-2267 ♦ www.nclabor.com HAZARD /ALERT! Occupational Safety and Health Division HOI Mail Service Center, Raleigh, NC 27699-1101 Dangers of Natural Gas Pipe Purging Into Buildings • Feb. 7, 2010: An explosion at the Kleen Energy Systems power plant construction in Middletown, Conn., killed six workers and injured 50 others. • June 9, 2009: An explosion at die ConAgra Slim Jim plant in Gamer, N.C.. killed four workers and injured 70 other workers. In addition, an ammonia refrigeration line was ruptured, forcing the evacuation of nearby schools. • May 1 9, 2008: One firefighter and 1 3 construction workers were injured following an explosion at a hotel under con¬ struction in downtown San Diego, Calif. All of these incidents had two diings in common. First, natural gas was allowed to vent into the interior of a building during the purging of gas pipelines. Second and most important, each of these incidents could have been prevented. What is natural gas? Natural gas is a fossil fuel consisting of a mixture of hydrocarbons, mostly methane, which is found underground or produced by the gasification of coal. Natural gas is colorless and odorless and is doped with small quantities of odorants, such as t-butyl mercaptan (described as having a “skunk-like” odor), to heighten an individual’s ability to detect its presence. W hy is natural gas hazardous? Natural gas is a highly flammable gas that readily bums in air and can explode when it accumulates in a confined space. The flammable limits in air for natural gas range from 3.8-6. 5 percent (lower explosive limit, “LEL”) to 13-17 percent (upper explosive limit, “UEL”). Natural gas is also a simple asphyxiant and will readily displace oxygen in air at higher concentrations. The immediately dangerous to life and health (IDLH) level is 1,200 parts per million (ppm). Please note that 1 percent is equivalent to 10,000 ppm. W hat industries and occupations arc at risk? Personnel who manage, install, maintain, repair, inspect, or place into operation fuel gas piping and equipment, including: • plumbers • gas installers • maintenance workers • contract supervisors • industrial facility managers How can natural gas explosions be prevented? Pinging new or existing gas piping into buildings can be highly hazardous due to the possible accumulation of gas above the lower explosive limit (LEL) and the associated danger of fire and explosion. Wherever possible, directly vent purged gases to a safe location outdoors, away from people and ignition sources. This can be done using a temporary hose or piping or permanently installed vent pipes, depending on the facility design. Purging indoors should only be done in limited circumstances where purging outdoors is not practicable. In such eases: ❖ nonessential personnel should be evacuated; ❖ all ignition sources should be controlled or eliminated; ❖ ventilation should be adequate to maintain the gas con¬ centration well below the lower explosive limit at all times; • Never rely on odor alone to detect releases of fuel gases. An odorant is typically added to fuel gases, such as natural gas and propane, to warn workers and consumers of releases. continued on раде 2 ConAgra Slim Jim plant in Garner, N.C., where unsafe gas purging caused an explosion in June 2009.