Gas leak at Porter Ranch – More than just methane?
Wednesday, 13 January 2016 at 12:29:PM
A 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.
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
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
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
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 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.