That's an excellent and practical question! I've seen people wondering this at parks and public barbecues myself. The short answer is: most standard urban trash cans are absolutely not designed to withstand hot barbecue coals, and doing so is a significant fire hazard.
While many public bins are made from durable, hard plastic or coated metal, these materials aren't engineered for extreme heat. A plastic bin can easily melt, warp, or even catch fire if direct contact is made with embers. A metal bin might not melt, but the intense heat can damage its protective coating, leading to rust, and more importantly, it can transfer heat to the surrounding structure or any flammable waste inside, like paper or food scraps.
The real danger isn't just the bin itself. The primary risk is that the hot coals can ignite a fire within the garbage, which may smolder for hours before erupting into flames, potentially causing extensive damage.
So, what should you do instead? The only safe way to dispose of hot barbecue coals is to let them cool completely first. Douse them thoroughly with water in a metal bucket or on non-flammable ground until they are cold to the touch. Once they are fully extinguished and cold, then they can be disposed of properly, sometimes in a designated ash bin if one is provided.
In summary, please never put hot coals directly into a public trash can. Taking that extra time to cool them down is a crucial step for everyone's safety.