Carbon dioxide is the key to many fire retardants. The common household items of baking soda and vinegar can be used to create carbon dioxide, according to Reeko's Mad Scientist Lab. First, fill a dish with baking soda. Place two candles of slightly different lengths upright into the dish of baking soda. Place the dish with baking soda into a large, empty bowl that will help contain spills. Light the candles and pour the vinegar into the baking soda dish. Make sure to avoid pouring the vinegar onto the candles. The baking soda and vinegar combine to create carbon dioxide which displaces oxygen used by the flame on the candle. The smaller candle will go out first, quickly followed by the second candle. This fire extinguishing method works because carbon dioxide is heavier than the surrounding air that the fire feeds on. Carbon dioxide therefore sinks to the bottom of the bowl and builds upward, displacing oxygen as it travels. Once the carbon dioxide reaches the same plane as the flame, it displaces the oxygen around it and extinguishes the flame.
While water can effectively be used as a fire retardant on certain fires, its fire extinguishing effectiveness can be enhanced with a household item. Adding detergent to water increases its ability to extinguish fire. Detergents lower the surface tension of water and allow it to absorb more oxygen from dry materials. Water is effective because it absorbs oxygen and cools the material the fire feeds on. In this science project, you create a fire in a safe environment and observe that when detergent is added to water, it takes less overall water to put out the fire.
Using candles, plastic soda bottles, baking soda, vinegar and a coat hanger, you can create an invisible fire extinguisher, according to Steve Spangler Science. First, cut the tops of two soda bottles. Wrap a coat hanger around a small candle so that you can lift the candle by holding only a coat hanger. Place vinegar and baking soda into the plastic bottle. Light the candle and lower it into the empty soda bottle. The flame will go out because of the carbon dioxide mixture. To expand on this experiment, pour the invisible carbon dioxide gas from one of the bottles into the second bottle by placing it at an angle steep enough for the gas to go into the bottle but not the vinegar. Place a newly lit candle into the bottle that has had its carbon dioxide transferred. It will stay lit. Then place the same candle into the bottle with carbon dioxide. It will go out.
Explore the effectiveness of different fire retardants by placing six similar-size squares each of cotton, rayon, paper, wool and polyester. Soak the six pieces of wool with experimental fire retardants of soap water, cornstarch, flour, baking soda Flame Guard and Flame Stop, according to the Super Science Fair Projects website. Repeat this for each of the remaining four materials. Let each of them dry for one day and then attempt to light them over a barbecue grill. Record the times it took for each material to light. The commercial fire retardants will come in first, followed by baking soda, soap water, cornstarch and flour.