The smoke shells used were 105mm artillery rounds which are fired from a distance into the airspace and have a larger spread than the more commonly used 81mm rounds, and 51mm rounds which are fired on the ground closer to target.
Lt Col Moorehouse said he had only used the 105mm rounds twice before and was forced to use them because stocks of 81mm had been depleted.
Captain John Anderson, who led a team of Royal Marines into compound 22, was thrown three metres into the air when the shell fell.
He said: “I looked across at the engineers and then Sapper Smith exploded in front of me.
“I thought because I saw his back touch the wall that he had leant against an IED in the wall which the Taliban had been planting.
“I could hear screams from those injured in the blast. It was just very smokey.”
Sapper Smith’s mother Helen Smith and half brother attended the inquest which is due to carry on for five days at Old Town Hall in Gravesend, Kent.