When I work in the garage, I keep all the doors open. Ten minutes after the pump engine was started. CO concentrations as high as 395 ppm were measured. In an Iowa case, an entire six- story hotel was filled with carbon monoxide from a single malfunctioning water heater located in the basement. Concentrations were as high as 600 ppm in a sixth-story room, a potentially lethal level.
Larger spaces decrease, and smaller spaces increase, the concentration of carbon monoxide.
If the mobile home was also tighter, CO concentrations would rise even higher. For those reasons, mobile homes are required to have only vented space heating appliances. Even large auditoriums, with ventilation, can quickly fill with CO from malfunctioning equipment. Use of LP-powered ice polishing machines in skating rinks have led to several cases of carbon monoxide poisoning in the U.S. and Canada, with concentrations above 100 ppm. A Canadian city prohibited indoor tractor pulls after they found that even with all outside doors open and ventilation fans operating they could not prevent carbon monoxide concentrations from rising above 400 ppm.