In addition, the National Transportation Safety Board still is coordinating the removal of components it wants to study to determine the cause of the Aug. 1 bridge collapse, the safety board said Wednesday. The NTSB said investigators will remain in Minnesota until November.

The NTSB is examining the de-icing system installed on the bridge in 1997, the chemical used in

the system and what type of corrosive properties it might have, NTSB said in its update.

The federal agency said investigators received records from the bridge designer and will assess the design calculations. In addition, a list is being drawn of projects and modifications performed on the bridge since its construction 40 years ago.

Thirteen people died after the bridge collapsed into the Mississippi River.