Natural gas leaks are ubiquitous in urban environments from outdoor street-level leaks to residential spaces. In indoor environments, where we spend 90% of our time, gas leaks happen even when appliances are turned off. While these baseline leaks are generally not hazardous from an explosion point of view, they could have implications for public health. A key question that arises is: “If natural gas is leaking, what else is in the gas?”
A team including Dr. Archana Dayalu of Verisk Atmospheric and Environmental Research explored this question by analyzing 234 samples of end-use natural gas collected from 69 different locations across three different gas utilities in the greater Boston area. Natural gas samples were collected directly from gas grills and stoves over a 16-month period spanning 2019-2021. The results were presented in an article entitled “Home is Where the Pipeline Ends,” published in the journal Environmental Science and Technology on 28 June 2022 and featured in major news outlets including the New York Times.
There were three key findings from this study:
- Natural gas used in homes contains numerous air toxics including the carcinogen benzene, which was detected in 95% of samples. While concentrations of air toxics were not high enough to be an immediate cause for concern, the finding was important considering:
- the widespread use of gas indoors with varying ventilation rates
- the significant variability in concentrations over space and time;
- the fact that in the winter (when indoor ventilation rates are lowest) concentrations of benzene were 3X higher than spring and 8X higher than summer concentrations Considering there are over 10,000 known outdoor natural gas leaks in Massachusetts alone, natural gas therefore poses an unknown and uncertain health risk.
- the World Health Organization exposure guidelines indicate there are no safe levels of exposure to benzene.
- we only know what we measure: other classes of chemicals of concern may be present.
- We could be exposed to small leaks – and therefore co-emitted air toxics – without knowing it. Natural gas odorant concentrations vary, with lower odorant levels in the winter. While odorants met explosion safety guidelines, they do not necessarily alert people to non-explosive but potentially concerning leaks from a public health (and climate) angle. This might also help explain how the aggregate of numerous undetected leaks result in large amounts of gas leaked from both indoor and outdoor urban environments.
- Leaking natural gas impacts climate … and now maybe health. Natural gas leaks were found to be an unknown and uncertain health risk. With over 10,000 known (outdoor) leaks in Massachusetts, natural gas leaks pose a potential air toxic exposure risk in indoor as well as outdoor environments. This was an important hazard identification study, with several implications for public health that warrant detailed exposure studies.
In recent years, increasing attention has been given to health risks of residential natural gas combustion. Our research has shown that health risks from residential natural gas use could result from exposure to not only burned gas, but unburned gas as well. However, as this work was a hazard identification study and not an exposure study, more research is needed to answer exposure questions.