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As the natural gas storage facility in the Porter Ranch neighborhood of Los Angeles continues to spew gas for nearly three months, the human face of this environmental disaster becomes even more pressing. As of Tuesday, close to 2,000 residents have been evacuated, two schools closed and the health department has linked hundreds of health complaints from nausea and vomiting to headaches and respiratory problems to two chemicals in the gas.

The health threat from this leak comes primarily from exposures to the chemicals known as odorants, tert-butyl mercaptan and tetrahydrothiophene, added to the natural gas to serve as a warning for leaks. The methane, which is the primary ingredient in the gas, is a powerful contributor to global warming and global ozone smog levels but is not toxic to the local community. The gas also contains low levels of other chemicals that can be harmful and the health department has recommended continued monitoring of the air in the Porter Ranch community to keep an eye on the levels of these contaminants.

So far, air testing in the neighborhood has not shown levels of pollutants tied to long-term health damage. But close scrutiny is needed as this drags on and it’s no longer a short-term incident. The following are important questions to answer if this leak extends for the additional two to three months currently projected.

What is the true pattern of low-level Volatile Organic Compounds (VOCs), particularly benzene, being detected in the community samples?

Current monitoring data show mostly very low levels of benzene with some scattered spikes that don’t exceed levels of concern for short-term events. However, the existing monitoring is not really set up to evaluate medium- to longer-term exposures. Continuous monitoring, rather than grab samples, that can reliably measure low levels, will be needed to paint an accurate picture of what’s going on and make sure we aren’t left with data gaps that limit our ability to assess health risks. This type of monitoring is also needed to better determine what levels may be due to the leak and what is coming from other sources.

Which areas are most impacted by the gas? Better data is also needed on the levels of the sulfur compounds—odorants and their breakdown products (e.g. hydrogen sulfide)—in the gas flowing out of this facility and in the ambient environment.

Current monitoring is not using sensitive enough testing techniques and this makes it difficult to understand what types of exposures are occurring. Some of the current testing is only able to detect levels of the tert-butyl mercaptan 50 times higher than the level where you expect to have health impacts from odors. We need more information that is able to narrow this gap and get us closer to understanding where the hotspots are.

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