A flash fire on a project located at Sunoco Logistics’ Nederland Terminal in Nederland, Texas, injured seven construction workers around 9 p.m. on Friday, Aug. 12.

Of the four workers that were critically injured, three of them were airlifted to area burn centers and remain hospitalized; the other worker was released on Aug. 17. Of the three still hospitalized, one was moved out of ICU to acute care on Aug. 19, and the other two continue to improve, noted Kelley McGill, president and CEO of L-Con, in a statement.

The three workers who were not critically injured were transported to area hospitals, treated and released. All seven work for contractor L-Con Inc. Additional details on those injured are not being released for privacy reasons, McGill said.

OSHA arrived on site on Saturday, Aug. 13, to begin the investigation. While the fire appeared to involve a crude-oil pipeline connection, the precise cause has not yet been determined. L-Con and Sunoco Logistics are working with OSHA on the investigation and each will conduct separate investigations into the incident.

L-Con’s team was performing welding operations in order to connect new tanks to one of the existing manifolds, explained Jeff Shields, communications manager with Sunoco Logistics. The fire occurred in the central manifold area of the terminal, noted McGill.

L-Con, a Houston-based contractor and construction management firm, serves heavy industrial clients in petrochemicals, refining and steel manufacturing. The firm recorded an Experience Modification Rate (EMR) of 0.53 in 2014 and 2015, including one lost-time incident in each year, with 1.43 million man-hours in 2014 and 801,876 in 2015.