Gasoline-powered generators are a lifeline during weather emergencies when electricity is unavailable, but they also emit poisonous carbon monoxide. So researchers at the National Institute of Standards and Technology recently conducted simulations to determine ways to prevent potentially dangerous levels of carbon monoxide from seeping into structures. Andrew Persily, a research group leader at NIST who worked on the study, said in the past it was recommended generators are kept at least 7 feet from structures. However, NIST now recommends first responders ensure generators are kept at least 25 feet away from structures.

"These generators put out a lot of carbon monoxide when they are running properly and if it gets into the building and the people are exposed to it at these higher levels than they are subject to the well-known risks of carbon monoxide exposure," Persily said.

NIST building researchers simulated multiple scenarios of a portable generator operating outside of a one-story house, using both a test structure and two different computer models — the NIST-developed CONTAM indoor air-quality model and a computational fluid dynamics model. Persily said they found that carbon monoxide can enter a structure through a number of airflow paths, such as a door or window. In addition, wind determines how the carbon monoxide moves around the structure.

"Think about which way the wind is blowing and don't put the generator on the leeward side of the building if you can avoid it because … the exhaust will linger there longer," he said.

Persily said firefighters responding to a large-scale emergency usually show up with a trailer or mobile command center, which is where people are working so "they must maintain a safe distance between the generator and the command unit so the carbon monoxide released by the generator has an opportunity to dissipate and not get pulled into their facility," he said.

In the next phase of the study NIST will model a 2-story house that researchers believe will interact with the wind differently. NIST researchers also have worked with the Consumer Product Safety Commission on related work.