Poisoning from CO (carbon monoxide) is a very common and very serious accident that can happen if generators are used improperly. Every proper precaution should be taken as it is a very serious danger. Portable generators should never be used indoors. This includes: basements, crawl spaces, garages, carports, and any other imaginable enclosed or partially enclosed space. They should not be used near open windows or inlets that may allow for exhaust fumes to leak in. CO is odorless, and invisible.