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Sour Gas

The Siren Call


The morning of the Venoco test siren, I stood in the Ellwood Preserve listening to birds chirp and water droplets fall from eucalyptus leaves to the carpet of gold-tinged grass. A thick ocean fog filled the air with the fresh smell of rain.

Later that morning, residents heard the slow rise and fall of the alarm—echoes that resembled the song of a whale.

Lisa Conti

If the siren was not a test but an actual disaster and a resident within ears’ reach of the alarm was shut up in their car, or, as one Indy reader inquired, surfing, what would each breath hold?

Fatalities due to accidental industrial gas leaks in the United States are, to date, restricted to plant employees. Such accidents often result in evacuations and community exposure. Last year, 4,000 people in Ohio were evacuated when an oil refinery sprung a sour gas leak. Closer to home, I’ve heard tales of a Mariposa Reina sour gas breach that occurred in the mid-1980s near Gaviota, that prompted evacuation of the nearby school and south to Santa Barbara.

On June 3 of this year, firefighters responded to a gas leak at ExxonMobil’s Las Flores Oil and Gas Processing Facility. (That’s the treatment plant just north of Refugio, on the mountain side of Highway 101.) The source: a faulty, hissing gasket. Venoco’s onshore Ellwood facility started processing sour gas in the 1970s. In April 1999, its offshore Platform Holly released gas for nearly 30 minutes. (Click here for more information on these facilities.)

Sour gas is defined as having qualified levels of hydrogen sulfide, a poisonous component that is also the source of its bad, sour smell. The physiological effects of the gas depend highly on the hydrogen sulfide concentration as well as the exposure time, both of which would depend on vapor levels, wind conditions, and humidity.

While a rotten egg odor is indicative of the gas, the intensity of smell doesn’t necessarily match toxicity. In fact, at high levels it’s been described as sickeningly sweet smelling. And at higher levels (10 times acceptable) olfactory paralysis can occur, which means the smell might go completely unnoticed.

After inhalation, the compound enters the bloodstream to have its effect on multiple tissues. Once in the system it is detoxified—at least in part. The body, in fact, produces and uses it, in comparatively low quantities. Namely it can alter blood pressure, relax musculature, and influence brain activity.

In the gut, where hydrogen sulfide is relatively abundant as a bacterial byproduct, specialized detoxifying enzymes transfer a sulfur atom to dampen its noxious component. The products, including sulfate, are then excreted into the urine. The sulfate in particular can be detected in the urine and is evaluated when exposure is suspected.

But when high amounts are taken in through breathing the heavier-than-air gas, the excess binds with enzymes in the mitochondria—the cell’s energy factory—and stops metabolism. This interferes badly with the body’s ability to use oxygen. The resulting effects on the nervous system culminate in an almost immediate collapse; what the industry calls a knockdown affect.

Independent of the brain, the eyes and lungs also find the substance intolerable well before the knockdown threshold. “Gas eye” is when the clear outer covering of the eye, the cornea, becomes swollen from irritation due to hydrogen sulfide gas. Similarly, the nose, throat, and bronchial passages can become damaged. In one account, in which a woman drove through sour gas 25 years ago, asthma brought on by the event remains an ongoing challenge.

When the siren sounds, the knee-jerk reaction of hightailing it out of the vicinity is advisable—complicated, however, by the flammability factor. Since cars are ignition sources and hydrogen sulfide is extremely flammable, Venoco Inc. advises that you stay in the vehicle with the windows up and vents closed, listening to the radio and waiting for the warnings to subside. The birds, butterflies, and surfers that won’t have the option will have to hope that the wind is in their favor.

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