What are the risks with incomplete combustion reactions?

Combustion is generally understood as burning of an organic compound. Since all organic compounds contain carbon and hydrogen, the products of a "complete" combustion of a typical hydrocarbon would include water vapor and carbon dioxide gas. Those being non-toxic present no problem to us. In fact combustion of methane (CH4) gas used for cooking can be done safely at home in the kitchen. A mixture of hydrocarbons, known as "gasoline" is used to fuel automobiles. Even though the exhaust of an automobile engine also contains mostly carbon dioxide gas and water vapor, it also contains some carbon monoxide gas, and some other hydrocarbon compounds that result from an "incomplete" combustion of gasoline. Incomplete combustion happens when insufficient oxygen is supplied to the fuel, and some of the compounds are not completely reacted with it. Carbon monoxide is especially dangerous because it is colorless, odorless and very toxic since it competes with oxygen for the hemoglobin in the blood stream, making it difficult for the blood to carry oxygen needed by all the cells in our bodies. Consequently, a person suffocates. Other by-products of incomplete combustion include black soot which is elemental carbon, not toxic, but messy. Other products may include hydrocarbon gases that may be toxic as well.