FAQ: Why do engines running indoors cause such a high risk of carbon monoxide death. Why do portable electric generators kill?

Short Answer: Because the levels of carbon monoxide in small engine exhaust are a thousand times higher than in a modern car and because the exhaust is being discharged or sucked into the indoor space.

From our video podcast with Gordon Johnson and Griff Winthrop:

Why do portable electric generators kill? Because the exhaust levels in the exhaust are at or above 87,000 ppm, which if it gets indoors, can kill in minutes. The generator pictured here poisoned hundreds of people attending an indoor wedding in Madison, Wisconsin, because the band was using it to power its equipment, in an indoor soccer wedding. 

Gordon Johnson: Let’s think about carbon monoxide happening from an automobile.

I’m old enough, and you’re almost old enough that you drove cars, that if you put them in the garage and left them running for five minutes, they might kill you. Today, our cars produce 1% of the carbon monoxide they used to. But let’s use the car in a garage as an example.

In the 1960s, muscle cars, the carbon monoxide that was coming out of the exhaust of that car was above 100,000 parts per million. If you sit in the garage with the car running, the entire garage is going to fill with carbon monoxide in a few minutes. Levels 20-50,000 parts per million in the breathable air. The ambient air of that garage or the inside of that car are going to make you unconscious, probably within 5 to 10 minutes, and kill you shortly thereafter.

When you lose consciousness, you’re probably two thirds of the way to death in very high CO ambient air situations.

Now take that and let’s use that example on a modern car. Alright? And we run into carbon monoxide events in cars a lot in today’s world. And the reason is these automatic push button ignitions.

You used to put a key in the ignition. Now you push a button to turn it off, or you turn it off with the remote in your hand. And especially cars that are hybrids, they’re very quiet. You pull in the garage and somehow or another, your process of turning the car off has gotten changed from the manual process of removing the key. Pull down the lever, put it in, park to push a button to put it in park and push another button to turn it off so the car may continue to run. Now, even though that car is now producing 1/1000 of the carbon monoxide that it used to produce when it’s outside. Over time, that carbon monoxide will build up in that garage. And why is that growth?

Griff Winthrop: Because it’s choking itself. It’s causing itself to have more and more incomplete combustion, because it is robbing itself of the oxygen it needs to completely combust its fuel.

Gordon Johnson: Let me see if I can give you some concept of percentages on this. So you start out with an atmosphere in in most places that you and I live of around 21% oxygen. The first time you cycle through that, you’re taking about 12% of the oxygen out of that to burn the fuel. So even though you may not have a tremendous amount of carbon monoxide on that first cycling through of that atmosphere, now it’s not running on 21% oxygen. It’s running on less.  And it goes down exponentially and over time, because the engine itself has used the oxygen that’s available in the room. Thus, the carbon monoxide levels will build up.

For more on the risks of generators running in or near homes, see the CPSC Proposed Rule with respect to requiring safety changes to portable electric generators, hosted on our website here, because the CPSC.gov has taken this document down since 2024.

We continue our conversation of the risk of generator exhaust getting indoors at this FAQ.