A new study confirms the presence of benzene in natural gas and the potential for undetectable internal leaks

New research has found that even people with an average sense of smell can be living with a natural gas leak and not know it. The study, published in Environmental Research Lettersfound that small gas leaks can affect indoor air quality by introducing a number of dangerous air pollutants, including carcinogenic benzene, which researchers found in 97% of natural gas samples in North America.

“Although these smaller leaks are not large enough to cause gas explosions, hard-to-feel leaks are common,” said lead author and PSE Healthy Energy scientist Sebastian Rowland. “The fact that they are so small makes them difficult to identify and fix, which can lead to a persistent indoor source of benzene and methane.”

The study is the first to assess whether gas leaks contain enough odorant to protect against elevated levels of benzene exposure, and provides the most comprehensive data yet on the composition of natural gas in homes.

Researchers from PSE Healthy Energy and Stanford University collected and analyzed 587 natural gas samples from 481 residences in 17 North American cities. The samples were tested for methane, hazardous air pollutants and sulfur-based odorants, and the researchers modeled the amount of gas that could escape without being detected by a resident with an average sense of smell. Their findings confirm that benzene and other hazardous air pollutants are present in nearly all natural gas supplied to homes, buildings and businesses across North America.

“Our nose is the first and only line of defense against gas leaks at the household level,” said PSE Senior Scientist Drew Michanowicz. “Given the differences in odor levels and the vast differences in olfactory ability among the general public, our findings really challenge the exclusive reliance on smell to protect people from gas leaks.”

Gas delivered to homes in Vancouver, Los Angeles, Calgary, and Denver had, on average, twice the benzene levels of the other cities, with benzene levels in Vancouver nearly fifty times higher than in the city with the lowest concentration, Boston. Odor levels in Houston gas were approximately five times higher than in Toronto, while neighboring cities New York City and Washington, DC, appeared to use completely different odor products, indicating a lack of standardization.

Measured natural gas odor levels should, on average, alert most residents to gas leaks that can lead to high benzene exposure; however, each household faces a different situation due to differences in personal odor sensitivities, ventilation rates, gas composition, and barriers to remediating leaks once detected.

The researchers suggest that regulators and consumers would benefit from greater transparency of natural gas composition, such as open access to natural gas composition data and regular sampling. In addition, improving leak detection through stricter odorization standards or increased use of leak detection equipment or reducing gas consumption altogether can improve indoor air quality and public health.