Many plumbing codes prohibit exposed drainage piping above food service areas. Is the piping considered exposed if there is a drop ceiling below? If so, would drywall ceiling help? Thank you.
NO. If there is a ceiling, be it a ACT or gypsum or something else, and the piping is above the ceiling, then the piping is "concealed" and is permitted to be installed there.
The issue has to do with dirt and bacteria collecting on the piping, (not just drainage piping) that can present a health hazard to humans that consume food prepared in that area.
Don't think a dropped ceiling will help unless you are referring to a true dropped ceiling (a second floor) similar to what is used in food processing and handling areas where the dropped ceiling is concrete with sealed openings.
Here is an example of a plumbing code.
CPC 318.0 Food-handling Establishments
Food or drink shall not be stored, prepared, or displayed beneath soil or drain pipes, unless those areas are protected against leakage or condensation from such pipes reaching the food or drink as described below. Where building design requires that soil or drain pipes be located over such areas, the installation shall be made with the least possible number of joints and shall be installed so as to connect to the nearest adequately sized vertical stack with the provisions as follows:
"318.1 All openings through floors over such areas shall be sealed watertight to the floor construction
318.2 Floor and shower drains installed above such areas shall be equipped with integral seepage pans."
The AHJ in many areas will call for drip plans or secondary containment under drainage piping. Would recommend that you review the issue with the local AHJ to review their expectations before you get too far along in your project.
bimr's approach has been what I have seen required.
Avoiding food prep areas whenever possible (vents are ok). If cannot, then try to avoid routing the piping over the equipment. If that is not possible, then drip troughs (sometimes with moisture detection) is required.