You will need to conduct a risk assessment to determine your actual risk. For one thing, listeria is found in soil / dirt so gravel over soil / dirt is not the best thing for parking lots and pathways into the facility.
It is good the pathway to the smoking area is seal, if the smoking area is sealed or cement. People likely take multiple smoke breaks during their shift and may only come and go from the parking lot once, or twice during their shift.
You will need to show how you prevent anything from the gravel and soil parking lot and pathways from coming into your facility include materials, chemical hazards (pesticides, weed control chemicals?), and biological hazards (pathogens such as listeria).