This takes place during Mission 7: Pont du Fahs Airfield
During the mission, you will come to the optional objective of "Destroy the bomb dump". To do this tactic you will need at least 2 sticks of dynamite which you can spawn with, or find them on enemies. This tactic should also work using other forms of explosives instead, like mines.
Clear out the area of enemies, and place 1 stick of dynamite next to the middle dump's explosive barrel. Place the other stick of dynamite close to the right most base so that it's close enough to get triggered by the middle explosion and set off the other dump. Now, prepare you flint and steel, and light it directly on top of the middle stick of dynamite, which will begin a 20 second counter.
Start running back, and get your sniper ready, aiming it at the left most dump's explosive barrel. As soon as your flint and steel timer is about to hit "0", shoot your rifle to destroy the barrel, and this should destroy all three dumps at the same time. Reference the video below for more information: