The primary gas associated with fire deaths that is a product of incomplete combustion is:

The primary gas associated with fire deaths that originates from incomplete combustion is carbon monoxide. This colorless, odorless gas is produced when carbon-containing materials, such as wood, gasoline, or propane, are not fully burned. Incomplete combustion occurs when there is insufficient oxygen to convert carbon fully into carbon dioxide, leading to the formation of carbon monoxide instead.

Carbon monoxide is particularly dangerous because it binds to hemoglobin in the blood more effectively than oxygen, reducing the blood's ability to carry oxygen to vital organs and tissues. This can lead to symptoms of poisoning, which may include headache, dizziness, confusion, and, at high levels, can be fatal.

In contrast, carbon dioxide is a normal product of complete combustion and while it can be present in high concentrations in closed spaces, it is less directly responsible for fire deaths compared to carbon monoxide. Carbon itself would not be a gas, and PVC (polyvinyl chloride) is a type of plastic that can release toxic gases when burned, but it is not the primary gas associated with fire fatalities.