So, the Bible is pretty amazing.
Egypt is experiencing a hailstorm from God that they have never seen not as a generation, but as a nation. All that is in the open dies from the hail. Pharaoh calls for Moses to come to him so he can ask him to pray that God would have it stop. Moses miraculously makes his way to Pharaoh's palace and back out of the city IN the hailstorm unharmed. Matthew Henry puts it well in his commentary in saying that peace with God, makes men thunderproof. Those whose sin has been dealt with already by the cross of Jesus Christ have no fear of God's judgment and wrath:
Observe, the place Moses chose for his intercession. He went out of the city (Exodus 9:33), not only for privacy in his communion with God, but to show that he durst venture abroad into the field, notwithstanding the hail and lightning which kept Pharaoh and his servants withindoors, knowing that every hail-stone had its direction from his God, who meant him no hurt. Note, Peace with God makes men thunderproof, for thunder is the voice of their Father.