The air supply is the most important part of the experiment, "We've got some gas monitors and back-up air supplies to make sure that the air quality stays at a high standard. If it doesn't then that's when I'll implement my back-up strategy." This strategy is, presumably, to get out of the box.
By sealing the box he is making a powerful statement, that much of what a human needs comes from a reciprocal cycle with nature. In the modern world we need to remember that the availability of air is reliant on plants, and isn't some commodity that can be bought in a supermarket.