Which gas is a common product of combustion encountered in structure fires?

• A. Benzene
• B. Carbon Monoxide
• C. Hydrogen Chloride
• D. Sulfur Dioxide

Answer: (B)

When fuels burn in a structure fire, conditions are not always perfect for complete combustion. If there isn’t enough oxygen or the fuel-rich mix dominates, carbon isn’t fully oxidized to carbon dioxide and carbon monoxide forms instead. This gas is especially concerning because it is colorless and odorless, so it can accumulate without warning while it reduces the blood’s ability to carry oxygen. Because incomplete combustion happens frequently in fires involving common building materials like wood, plastics, and textiles, carbon monoxide is a typical, expected byproduct you’ll encounter on a structure fire scene. The other gases can appear in certain situations—hydrogen chloride when chlorine-containing materials burn, sulfur dioxide from sulfur-containing fuels, and benzene from some hydrocarbon smoke—but they’re not as universally produced across typical structure-fire conditions as carbon monoxide, making it the most common byproduct to recognize.