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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Law of the land will decide what you need to do. you should talk with the people who passed your business license. rule all over the world are not the same and also it may be different from one city to another in the same country. still you can try out on this forum by putting more details on the board.
You need to hire a qualified, responsible civil engineer or licensed contractor. This person will be responsible to first know where your car parking facility resides and second how to find out and interpret the local safety codes. Lives are at stake here and you want to come from here with the cheapest answer so you can blame somebody else. Sorry but by just asking us this question with even giving us a hint as to where this parking resides, I can safely say that you are dangerously incompetent. You are so incompetent that you cannot post this question in the correct forum.
If you're not actually involved in building a parking facility evacuation system and this is school work, then tough noogies. CR4 is not a homework cheat site. If you really are trying to palm off personal safety onto us, then I recommend you return everything you've been paid and all of the plans of what you've done to the owner of this parking area. This will likely be your cheapest recourse compared to the liability suit you would clearly lose.
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"Don't disturb my circles." translation of Archimedes last words