Investigators are piecing together what sparked an oil tank fire on Wednesday that killed one person at a wellsite in Weld County, CO operated by Denver-based Great Western Oil & Gas Co.

Forty firefighters from four separate county stations doused the blaze around 10 p.m. MT Wednesday, about four hours after they were called to the site east of Windsor, CO, about 59 miles north of Denver.

Great Western spokesperson Susan Fakharzadeh said company employees are heartbroken over the death of a crew member. “We’re on site conducting an investigation with first responders and the Weld County Sheriff’s Office, and we hope to have more information soon,” Fakharzadeh told NGI’s Shale Daily.

An unspecified number of wells are shut in during the investigation. “What we find out will determine the short- and long-term impacts on our operations,” she said, adding that the fire was “relatively small” and affected two storage tanks.

For Weld County, where the bulk of Colorado’s oil and gas development is underway, this is one of the region’s latest serious incidents.

In 2017, one person was killed and three people were injured at an Anadarko Petroleum Corp. oil tanker site in the county near Mead, CO. Also two years ago in Firestone, about four miles from Mead, a house explosion killed two men and severely injured a woman following a leak from a disconnected natural gas well flowline, which triggered regulatory reforms in the state.