The deaths of four oilfield workers since 2010 have prompted NIOSH to ask oil and gas firms to help the agency assess the health hazards associated with hydraulic fracturing.

In a May 19 blog post, NIOSH officials point to four worker deaths at well sites in the Williston Basin in North Dakota and Montana that might have occurred as a result of “acute chemical exposures during flowback operations.” Flowback, the agency explains, “refers to process fluids from the wellbore that return to the surface and are collected after hydraulic fracturing is completed.”

“While not all of these investigations are complete, available information suggests that these cases involved workers who were gauging flowback or production tanks or involved in transferring flowback fluids at the well site,” NIOSH officials wrote in the blog post. “Often these fatalities occurred when the workers were performing their duties alone.”

While safety hazards in the oil and gas extraction industry are well-known, the agency acknowledges that “there is very little published data regarding occupational health hazards (e.g., types and magnitude of risks for chemical exposures) during oil and gas extraction operations.”

“To address the lack of information, NIOSH requests assistance from oil and gas stakeholders in further characterizing risks for chemical exposures during flowback operations and, as needed, develop and implement exposure controls,” NIOSH officials wrote.  

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Fluids returned during flowback operations contain volatile hydrocarbons, NIOSH explains. Liquid hydrocarbons from the separation process are routed to production tanks, where workers periodically monitor the fluid levels with handheld gauges (sticks and tapes) through access hatches located on the tops of the tanks.

While exposure to hydrogen sulfide – also known as “sour gas” – is a well-recognized hazard in oil and gas extraction, NIOSH asserts that many of the chemicals found in volatile hydrocarbons are acutely toxic at high concentrations. Volatile hydrocarbons can affect the eyes, breathing and the nervous system, and at high concentrations also can cause abnormal heart rhythms, according to the agency.