SQ7 o/s had a code 3 fully involved on a detached garage. SQ7 initiated fire tac. E7 took command at first. Fire tac advised that there is ammo in the building. E1 pulled a water to supply to E7 who pumped the fire. E7 advised command that there were also lawn mowers and gasoline in the building. E7 was exposure protection, and advised that the exposure to the southwest (the House) had fire in the attic.