If you see the flash, take cover and get low to reduce the effect of the shockwave. If you hear the blast or have felt the shockwave take cover to avoid debris.
Move away from the debris cloud.
If you cannot get away from the debris cloud, cover your mouth with a folded cloth and exit the cloud as soon as possible.
If you get debris on you, remove your clothing. Then, using a scrub brush, wash the affected area with soap and water.