The short answer is yes, but the longer answer is more complex. Unless the fireplace is ventless by design, you’ll need some type of exhaust pipe system to safely send fumes and other harmful byproducts out of the house. Even then, ventless fireplaces are not always permitted because they do keep the byproducts inside of your house. Ventless fireplaces are safest when installed in spaces that are themselves well-ventilated, like large rooms with lots of windows.

No, but they both serve distinct life-saving purposes. Smoke detectors primarily sense the presence of smoke, typically caused by a fire, and emit loud alarms to alert occupants to evacuate. In contrast, carbon monoxide detectors monitor the levels of carbon monoxide gas, an odorless and colorless but deadly substance produced by incomplete combustion of fuels. When CO levels become dangerous, CO detectors sound alarms to warn inhabitants of potential poisoning risks. 

No, it is not safe to use an outlet that sparked. A spark from an outlet could indicate a short circuit, loose or frayed wiring, or other serious damage. Continuing to use an outlet that sparks can increase the risk of electrical shock, electrical fires, and other hazards. It's important to turn off the power to the outlet at the circuit breaker if possible and avoid using the outlet until a licensed electrician has inspected and repaired it.

You can let a fire burn out in a fireplace as long as you or someone else will stick around to monitor it until it goes completely out. This may take several hours. To prepare, stop adding fuel to the fire well before you’re ready to call it a night. If you’re using the fireplace for warmth, you’ll want to cover up in some blankets as the flame dies down.