"We will shortly be seeking expressions of interest from prospective bidders for the design and installation of a fire suppression system for both roadtunnels at the Dartford to Thurrock River Crossing," said an Agency spokesman.
Halcrow fire safety director Dr Fathi Tarada said retrofitting sprinklers at Dartford was needed as closure following a fire would result in heavy toll revenue losses for its operator. It would also put pressure on other routes.
He added that the Dartford tunnel needed a fire suppression system because of restrictions on emergency access.
"There is only one cross-passage between the two tunnels, which was designed for construction access rather than evacuation, is narrow and has a large slope," said Tarada. "A fire suppression system can cool the temperatures down and allow evacuation in safety."