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.

While a hot fire can help heat up and loosen tar within your chimney, making it a recommended step before using a creosote log, it will not burn off significant existing buildup on its own. Attempting to remove built-up creosote with a hot fire is dangerous and can cause a chimney fire. For safe and effective removal of caked-on creosote, the best approach is to hire a professional chimney sweep.

Baking soda is an effective fire reduction method. However, flour and baking powder are very dangerous around flames. Flour is flammable and it can also conduct electricity. The combination can cause serious injury from electrical shock and worsen the situation by adding fuel to the fire. Baking powder is also not an option as it's also highly flammable. 

Yes, fire extinguishers eventually expire. However, the good news is that a properly stored fire extinguisher can last a decade or longer. They don’t have an expiration date on the canister, but you can check the manufacturing date on the “UL” nameplate near the classification information. Maintenance will also give your fire extinguisher longevity. Check the gauge at the top of the extinguisher every month. You'll want to make sure the gauge needle is in the green section, and if a hose or nozzle has been used or damaged, you need to replace it.