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Gas leak at Porter Ranch – More than just methane?

Wednesday, 13 January 2016 at 12:29:PM

CaliforniaA new year brings news from a suburb of Los Angeles, California, where there’s been widespread concern over the health impact of a leak of natural gas.

Enormous scale

This isn’t just any old gas leak, though – it’s on a massive scale, and has even led to the evacuation of thousands of residents and the declaration of a state of emergency.

Venting from a depleted oilfield now used to store natural gas, about 60,000 kg of methane were escaping each hour into the atmosphere at the incident’s peak on 28 November 2015. By mid-December, that had increased the state’s annual methane emissions by about 25%.

The leak, which is coming from the Aliso Canyon Underground Storage Facility, likely originates from a 7-inch hole in a pipe about 500 feet below the surface (see this article in the Los Angeles Times for more). This depth makes it very difficult to deal with, and attempts by the facility owners SoCalGas have so far met with failure.

Effect on local communities

tert-butylthiol molecule

The impact of this gas leak goes far beyond worries about methane explosions and methane’s potent contribution to the greenhouse effect. Since the leak began on 23 October, residents of the community of Porter Ranch a mile or so to the south have been complaining of offensive odours, headaches, nausea and nosebleeds.

SoCalGas, although regretting the incident and taking action to deal with the leak, play down the risk to local communities by saying “Scientists agree natural gas is not toxic and that its odorant [presumably the commonly-used compound tert-butylthiol] is harmless at the minute levels at which it is added to natural gas.” Strictly speaking this might be true, but generalisations like this, usually founded on narrow lab-based studies, should be applied very cautiously to long-term exposures of large populations. Anyway, even if no ill effects were apparent, the point remains that large quantities of chemicals have been released into the environment, which is hardly socially or environmentally responsible.

More than just methane?

And let’s not forget that natural gas isn’t just methane with an added odorant. Apart from common components of the atmosphere such as carbon dioxide, water and nitrogen, it also contains significant quantities of higher hydrocarbons. Many of these ‘hazardous air pollutants’ have well-documented harmful effects, as recognised by their inclusion in air quality regulations such as the US Clean Air Act.

So what are these other emissions, and how might they be contributing to local poor air quality? That’s where our equipment comes in. The South Coast Air Quality Management District (SCAQMD) – the regional air pollution control agency – have recently acquired one of our CIA Advantage canister autosamplers, which takes samples collected into 1-litre or 6-litre air-monitoring canisters, and concentrates the vapours before passing them in a gas chromatograph for analysis.

The analyses they’ve released show the presence of a number of indicators of poor air quality, including propane, butane and pentane isomers at levels well above typical background values. I’m not suggesting that these compounds are necessarily the cause of the health effects reported, but it goes to show that the situation is more complicated than it might first appear.

In summary, no-one actually knows exactly which chemicals might be to blame here – as I’ve mentioned before on this blog, untangling cause and effect in studies of the effect of chemicals on health is notoriously difficult. However, the more information there is on the airborne pollutants at Porter Ranch, the better… and we’re pleased that our equipment is helping to fill that knowledge gap.

David Barden  


David BardenDavid Barden received his Ph.D. in Organic Chemistry from Cambridge University in 2004, and during his time as an editor at the RSC wrote news pieces for Chemistry World on various scientific topics. He is now Technical Copywriter at Markes International, where he draws on the expertise of his colleagues to explain how new thermal desorption and mass spectrometry technologies can be applied to analyse volatile organic compounds in a wide variety of situations.


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