Which of the following is the most prevalent toxic fire gas?

Carbon monoxide is considered the most prevalent toxic gas produced during fires due to its common formation from the incomplete combustion of organic materials like wood, paper, and various fuels. It is particularly dangerous because it is colorless, odorless, and tasteless, making it undetectable by humans without specialized equipment. In an enclosed space, the accumulation of carbon monoxide can quickly reach levels that are lethal, often leading to fatalities before individuals even realize they are in immediate danger.

This gas interferes with the blood's ability to carry oxygen, leading to suffocation at the cellular level. While other gases like hydrogen cyanide, carbon dioxide, and formaldehyde also pose significant risks during fires, carbon monoxide’s prevalence and the speed at which it can accumulate make it the foremost concern for firefighters and first responders in fire scenarios.