Is the death of a neighbor—who helped extinguish a fire that accidentally broke out—considered accidental killing, and what are its consequences?

This is not a case of accidental killing, for the neighbor himself voluntarily undertook to extinguish the fire and did not pay close attention, thus causing harm to himself. Therefore, the questioner is not obligated to pay any blood money (Diyyah) or expiation (Kaffarah). He should, however, pray for the neighbor and seek forgiveness for him.