Lt-Col Mike Watkins, 51, was killed when earth fell on top of him as he looked for the entrance to a wartime tunnel in Vimy Ridge, near Arras, the Ministry of Defence said.
Lt-Col Watkins, who was married with one son, was head of safety at the Directorate of Land Service Ammunition, based in Didcot, Oxfordshire.
He was in France to help survey a system of tunnels which are still thought to contain a large number of unexploded charges.
An MoD spokesman said: "The tunnels are quite a complex system, and nobody really knows where they all are. It appears the ground gave way."
Television producer Marc Sinden, who had been making a documentary series with Lt Col Watkins about the work in the tunnels, called the death "a terrible loss".
Mr Sinden said Lt Col Watkins was "a hero who had saved countless lives through his bomb disposal work. This man was the one true hero I have ever met. He single-handedly saved more lives than I can possibly imagine."
Lt Col Watkins' work was often secretive and undercover, and it would have put him in danger to publicise his action while he was alive, Mr Sinden added.
"But now he is dead it does not matter. I admired him more than anyone I have ever met, and I want people to know what he did."
He said a network of 20 miles of tunnels packed into a small area of land had been uncovered by Lt Col Watkins' team. These were "littered" with leftover explosive charges, one under a motorway and others beneath the Canadian war memorial.
"It was a very dangerous operation, which Mike was doing as much as a hobby as anything else. This man was a serious hero."
Bomb disposal experts in England were meanwhile uncovering a stack of more than 20 unexploded practice bombs in a garage in Warwickshire.
The shells, believed to have been used by the RAF for bombing practice during the Second World War, were uncovered by staff at Johnson Coaches in Henley in Aspen. Eight more, with live detonators, were found earlier this month under a pile of rubbish at the coach company's site on the A3400.
Inspector Les Twynholm of Warwickshire police said: "They would only be dangerous if you were standing nearby."Reuse content