Which gas is commonly a product of combustion that is harmful when inhaled?

Inhalation of carbon monoxide is particularly dangerous because it is a colorless, odorless gas that can bind to hemoglobin in the blood more effectively than oxygen can. This reduces the blood’s ability to carry oxygen throughout the body, which can lead to severe health issues, including carbon monoxide poisoning. Even low levels of exposure to this gas can cause symptoms such as headaches, dizziness, confusion, and can ultimately lead to loss of consciousness or death in higher concentrations. This makes carbon monoxide a key concern in fire scenarios where combustion occurs, as incomplete combustion often produces it alongside other combustion products.

In contrast, oxygen is essential for combustion and is not harmful when inhaled at normal levels. While carbon dioxide is a common byproduct of combustion and can be harmful in high concentrations, it is typically not as immediate a threat as carbon monoxide in emergency situations. Hydrogen is flammable and can be a product of certain chemical reactions but is not a direct product of typical combustion processes involving organic materials. Thus, among the options, carbon monoxide stands out as a notably harmful gas produced from combustion.