Although the most hazardous stage of charcoal grilling happens when you light it -- over-enthusiasm and lighter fuel can combine to disastrous effect -- the clean-up phase is not without risks. In particular, you should not underestimate embers that appear to be in their death throes. Never touch a grill that might be hot and keep everyone away until you're sure it's safe.
Prepare to bring a grilling session to an end by wearing heatproof mitts, removing the grill rack, covering the grill with the lid and sealing off any vents to cut off the oxygen supply. The Hearth, Patio and Barbecue Association recommends letting the coals burn out completely as the safest way to extinguish a grill. Because it is not always clear with gray coals whether they are still burning or not, let the ashes cool for up to 48 hours before preparing for disposal. In rare cases, ashes can reignite up to 72 hours after the grilling is done. Once the charcoal is out, sift through the ashes with a metal spatula or tongs and reclaim any unburnt bricks, which can be moved to the side and reused.
Getting Rid of the Ashes
Once the ashes are cold, tip them onto a sheet of aluminum foil and wrap them before disposing of the package in a container that won't melt or burn. Even the most unobtrusive ember can burn through a paper or plastic container, so a metal trash can is best. When sweeping out the ashes from the grill, watch out for sparks, especially in a breeze. Any type of grill, whether charcoal or propane, should be set up outside, away from buildings, dry brush or leaves. Never bring the grill inside to clean it, as an active grill produces lethal but odorless carbon monoxide.
However dramatic it may look, never pour water directly over hot coals, even if they appear to be out. Coals can burn at 1,000 degrees Fahrenheit, and dousing them with water can crack the grill. Also, the water can convert immediately to steam, spreading a puff of ash over everything and potentially causing burns. If you need to extinguish a grill in a hurry, you can use a bucket of sand, but be aware the sand will be hot for a while. Alternatively, you can remove hot coals individually with long-handle tongs and drop them into a metal bucket of water.
Remove any remaining cold ashes with a trowel or metal spatula and clean out the grill thoroughly, especially the vents. Brush down the grate with a wire brush and lubricate the parts with silicone spray.