Substitute. Substitute chemicals for other products that are less harmful. While there will never be a completely environmentally best way there are often better ways. The use of water based, instead of solvent based, paints is a good example.

Suppress. The next best way to make for cleaner production is to suppress the substance escaping. Using water or air jets to suppress dust is a classic example.

Enclose. If that was impossible, enclosure was considered next. An obvious example is noise - it is best to suppress it, but if that is not possible, keep it inside an enclosure rather than let it deafen or annoy everybody.

Ventilate. CP tries to avoid relying on ventilation as this is expensive and wasteful and is the last resort.