US federal job safety regulators have cited four employers, including the largest oil and gas producer in Colorado, for exposing employees to health and safety hazards in connection with a May 2017 explosion at a tank battery construction project that left one employee dead and three others with third-degree burns.

The companies face over $70,000 in proposed penalties, according to a statement released  by the US Department of Labor's Occupational Safety and Health Administration.

The companies cited are Anadarko Petroleum, Energes Services, Dominguez Welding and Unlimited Services.

Workers were merging two tank batteries into a single battery operated by Anadarko in Mead in May 2017 when the explosion and fire occurred. OSHA inspectors found that flammable vapours or gases ignited as employees worked near pipes connected to a crude oil tank.

Oscar Lopez Velasquez, 32, of Greeley, died in the May 25 explosion in unincorporated Weld County in the 6400 block of Colorado 66.