See: Tier 1 Spill. See: Tier 2 Spill.
Oil spills...happen. Sometimes, these situations don't amount to much. The oil company itself can send out its sweepers and moppers, and get everything back to normal. That event is considered a tier 1 spill. Sometimes, the spill gets away from the oil company and the authorities need to get called in to help with containment and clean-up. A tier 2 spill.
Then...you have the bad ones. The global-level events. The oil spills that lead every news outlet for weeks. The kind of situation that spawns Congressional hearings. Now...events have reached tier 3.
A tier 3 spill represents the most serious stage of the three-tier system put in place by the International Petroleum Industry Environmental Conservation Association, or IPIECA. It represents a massive event that requires a large influx of outside help.
