Most people expect fire to be light. On the contrary, fire is pitch black. Smoke kills not flames. The poisonous gases emitted by a fire actually put people into a deeper sleep and many suffocate without ever waking or even becoming aware of the fire. They die of smoke inhalation because they had no warning.
Fire has intense heat.
Fire can cause the temperature to rise several hundred degrees in just seconds. The heat is so intense that it can cause the human body to stop functioning altogether - one breath can cause severe lung damage. The heat alone can cause someone to become unconscious and not be able to escape. There is no time. There is no time to waste.