If you use proper fuel sources (well-seasoned wood) and maintain proper ventilation throughout your chimney, you shouldn’t be concerned about carbon monoxide poisoning. While the gas is dangerous, a healthy fire does not release enough of the gas to make it deadly. A good rule of thumb for preventing CO poisoning is to install smoke and carbon monoxide alarms on every level of your home, and to always make sure you are using your damper when having a fire.