LOS ANGELES (AP) — Los Angeles County public health officials are seeking independent researchers to study the short- and long-term effects of the nation’s largest-known natural gas leak on the health of people who lived in nearby communities.

The county Department of Public Health announced the request for proposals in a statement Tuesday.

Thousands of families were sickened and had to leave their homes due to the 2015 blowout at Southern California Gas Co.’s gas storage facility in the Santa Susana Mountains on the northern edge of Los Angeles.

More than 100,000 tons of methane gas were released into residential communities surrounding the facility over 111 days.