This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Both metal and copper oxidize when exposed to oxygen and this is a natural process. Copper that is exposed to the outside environment is more likely to turn green and that is why copper vases and decorative pieces in gardens are often green.
Copper can get blue or green stains, due to oxidation. Moisture, temperature and the level of pollution all cause copper to oxidize. The stains are only on the surface and don't cause the material to become weak. It becomes harder to remove the stains when they're present for a large amount of time, because they settle in the material.