404.1 Personal Cooking Appliances. Personal appliances such as gas or propane camp stove, portable barbecue or hibachi, may be used under the following conditions:
a). Placement in an area that will not scorch, burn or otherwise damage lawns or table tops.
b). Placement in an area at least 30 feet from any flammable material such as grass, weeds, wood chips, brush or buildings.
c). All burning fuel such as wood or charcoal is thoroughly extinguished before being disposed of in an existing fireplace, fire pit or barbecue grill. It is unlawful to dispose of coals in garbage cans or refuse bins.
Looks like from all the research that i did, that it is unsafe to throw coals out in the garbage. This makes sense, as even splashing water on them does not guarantee that they will not remain hot internally. It would be crazy to throw a cig. in the garbage.

The IDEAL way to get rid of coal is either 1) soak them in water for 24 hours and then put them in the garbage, or 2) submerge them in water and then put them in a metal tin sealed tightly. Since neither of these options were available, i feel like the side of the parking lot was the best solution.

but what do i know.