What is the maximum height and width speed bumps are allowed to be.?
Dry ice should be fine. Being denser than air, it will hug the floor and so shouldn't set off any smoke detectors. The only word of caution is that you need to keep the school ventilated. By all means use dry ice machines, but keep corridors open and don't over fill any room with smoke. Being carbon dioxide, dry ice can be deadly if allowed to build up to dangerous levels as it will suffocate. If you are hiring the machines, the hire company should tell you all the safety info about how much dry ice to use and keeping the area ventilated etc.
A plain, black sheet of paper would be accurate, if not very artistic.
