When an accident happens, your immune system cues up your internal fire alarm: your response. Instead of sirens, it uses chemicals to get the message out and instead of smoke or fire you sense redness, swelling, heat, and pain.

Immune

Explanation: When an accident happens your immune response is the response that uses chemicals which may cause redness, swelling, heat, and pain

i am going to guess that it is co2.

burning fossil fouls really decrease the carbon in the atmosphere so b