That's an excellent and very important question. Disposing of hot ashes carelessly is a major cause of fires, especially in urban areas where trash is compacted and collected frequently. The absolute best way is to never put hot ashes directly into any trash can, especially a plastic one. Here’s the safe, step-by-step method you should always follow:
First, let the ashes cool completely in your fireplace, grill, or fire pit. This can take many hours, even a full day. Do not add water to speed this up, as it can create a dangerous steam cloud and make a messy slurry.
Once they are no longer emitting heat, carefully transfer the cold ashes using a metal shovel into a dedicated, metal ash bucket with a tight-fitting metal lid. Never use plastic, paper, or cardboard containers. Place this metal bucket on a non-flammable surface like concrete or dirt, away from your home, deck, or any flammable materials.
Let the ashes sit sealed in this metal bucket for another 24-48 hours. This ensures any hidden embers are fully extinguished.
Only after this waiting period should you consider disposal. For final disposal in your urban trash can, double-bag the cold ashes in heavy-duty plastic bags to contain the dust. Then, place the bagged ashes at the bottom of your trash bin. Do not place them on top of or near other combustible materials like paper or packaging.
The core principle is patience. Rushing this process risks a smoldering fire igniting inside your trash can or in the garbage truck, endangering property and lives. When in doubt, wait longer. Your safety and your neighbors' safety are worth the extra time.