After Sgt Matt Thomson (Guy Pearce) set the charges on the bomb, he crosses the 25 m radius (what Sanborn called the kill radius) and then he even starts running when Eldridge starts running towards the guy with the phone. So when the blast happens, even though no physical damage is seen on the bomb suit, what is it that killed Matt Thomson?
Sgt Thomsons' brain was severely injured, along with other potential damage due to the shock wave created by the Improvised Explosive Device.
According to IED Impacts: HowStuffWorks...
When the primary charge explodes, gases heat up and expand rapidly outward under pressure. The expansion creates shock waves or blast waves. The waves travel outward at about 1,600 feet per second (488 meters per second) over hundreds of yards or more depending upon the amount of explosive.
The pressure in a blast wave can be on the order of 1,000 times atmospheric pressure. This intense pressure can rupture your eardrums and slam your brain against the inside of your skull, which leads to concussion, blindness, deafness and swelling of the brain. In addition, many air-filled tissues and organs such as the lungs and bowels can be perforated by the pressure changes. The type and extent of the injury depends on the person's location relative to the IED. A person in the primary blast radius can be hit by pressure changes, heat and shrapnel. Most likely, this person will die.