Fireplace inserts don't make homes safer, but they can prevent burning material from exiting the structure, potentially preventing fires. If they're installed incorrectly, however, they can pose safety risks.
Fireplaces are one of the older methods of heating a home, but their chimneys vent most of the heat generated outside the home. Fireplace inserts can be used to convert a chimney into a gas heater vent, allowing homeowners to take advantage of far more economical heating. However, they still have to provide sufficient airflow out of the home; backed-up inserts can cause carbon monoxide and other gases to stay in the home. They also must be installed carefully, which can be difficult on older chimneys. When used correctly, they are as safe as any gas heater ventilation system.