Watch: Infrared video shows Porter Ranch leak spew 50,000 kilograms of methane per hour

A black vapor plume boils up from a point on a hillside in Aliso Canyon and spreads as a low cloud, hugging the landscape, moved along by a breeze. It's footage from a camera calibrated to make gases that would normally be invisible show up on video.

The short video was shown Tuesday evening to Porter Ranch residents worried about the potential health consequences of  a massive methane leak from Southern California Gas Co.'s Aliso Canyon natural gas storage field.

"Making things visible makes it real to people who can do something about the problem," said cameraman Alan Septoff of the environmental nonprofit Earthworks, which created the video. The groups is distributing the video in support of a class action lawsuit against Southern California Gas Company.

The leak is spewing from a natural gas well that ruptured about Oct. 23, pouring out an estimated 50,000 kilograms of methane per hour. The utility has been unable to stop the leak and its accompanying rotten-egg smell from a chemical used to add an odor to the gas. So Cal Gas has relocated more than 700 Porter Ranch area families to hotels, is assessing the relocation requests of 2000 more families. The company is also facing lawsuits from Los Angeles city and county, and a class action lawsuit from residents.

The environmentalists shot the video on Dec. 2 and 3 using what's called a forward looking infrared camera calibrated to detect gases, said Alexandra Nagy of Food & Water Watch. She said she and the cameraman hiked to a couple of vantage spots outside the 3,600-acre Aliso Canyon natural gas storage field owned by So Cal Gas.

Nagy's group has been working with local environmental group Save Porter Ranch, which is a plaintiff along with residents who have sued the gas company and the state Division of Oil, Gas and Geothermal Resources over the leak. Residents allege they have been forced from their homes by the smell and that the value of their homes has been harmed by the gas. Some 1,350 complaints of the odor have been made to the South Coast Air Quality Management District.

Despite having ordered So Cal Gas to relocate so many families, Los Angeles County Public Health Department says short term health risks from the methane gas are low because it rises into the atmosphere.

The health risks from mercaptans, a chemcial used to add a detectable rotten-egg odor to natural gas, are also low in both the short and long term, although some vulnerable individuals may be affected more than others, interim Public Health Director Cynthia Harding told members of the Board of Supervisors in a Dec. 1 letter.

However, the longer the leak persists, the more likely it is that trace levels of toxic emissions in the methane (hydrogen sulfide, sulfur dioxide, benzene toluene, ethylbenzene and xylenes) could produce significant long term health effects, she said. Benzene is a known carcinogen.  Radon, the leading cause of lung cancer in non-smokers, occurs naturally in geologic formations like the underground gas storage areas. It could also be released as the leak is repaired, Harding's letter said. She recommended the county monitor the air quality at Aliso Canyon and around Porter Ranch.

Porter Ranch is a community of about 30,000 residents in the north end of the San Fernando Valley. The closest homes are about a mile away from the Aliso Canyon natural gas field.