What is the primary cause of death resulting from automobiles exhaust accumulation in garages?

The primary cause of death resulting from automobile exhaust accumulation in garages is carbon monoxide. Carbon monoxide is a colorless, odorless gas that is produced during the incomplete combustion of fossil fuels, including gasoline used in vehicles. When a car is running in an enclosed space like a garage, carbon monoxide can accumulate to dangerous levels because it is not effectively ventilated.

Exposure to carbon monoxide can lead to poisoning, as it binds to hemoglobin in red blood cells more effectively than oxygen, reducing the blood's ability to carry oxygen to tissues and organs. This can cause symptoms ranging from headaches and dizziness to unconsciousness and death, especially in situations where individuals are unable to escape the accumulation of this toxic gas.

In contrast, the other substances listed are less relevant in the context of automobile exhaust in garages. Methane, while a greenhouse gas, is not a significant byproduct of automobile exhaust. Ethylene dioxide is not typically associated with vehicle emissions and is a chemical used primarily in industrial applications, and tetraethyl lead, once used as a gasoline additive, has been phased out in most places due to its toxicity and environmental impact. Therefore, carbon monoxide stands out as the primary concern due to its direct link to fatalities in enclosed spaces from car exhaust.