Both OSHA and the U.S. Chemical Safety Board (CSB) are investigating Thursday’s explosion at the Williams Olefins plant in south Louisiana -- which was followed a day later by another fatal chemical plant blast only a few miles away.

Two workers died and 77 were injured in the first incident at a plant which produces ethylene and propylene, highly flammable gases which are widely used in the petrochemical industry. Some of those injured suffered burns and are being treated in local hospitals. At least one burn victim is listed in local condition, sources report.

In the second accident, which occurred Friday night, one worker was killed and seven others were injured in an explosion at a CF Industries chemical plant only a few miles from the Williams Olefins plant.

The victims of the first explosion have been identifed as 47-year-old Scott Thrower and 29-year-old Zachary Green. Thrower had worked for the company since 1999; Thrower since last October. His body was found by hazmat crew searching the site after the blast.

The cause of Thursday’s blast hasn’t yet been determined, but the FBI has ruled out terrorism.

The Louisiana Department of Environmental Quality tested the air around the Williams Olefins plant for pollutants that may have resulted from the explosion and reported that there were no pollutant levels of any concern.