The Coast Guard uses these routine and frequent regulations to establish control of access to maritime areas to ensure the security of vessels, waterfront facilities, or individuals. Many of these zones are of short duration, a few hours to a few days, and all are geographically limited in area. Security zones are established for Presidential or Vice Presidential visits, high-profile events such as the Olympics, controversial events such as transport of spent nuclear fuel, and in response to the threat of terrorist attacks. Some security zones are implemented only at heightened security levels and only for the duration of the heightened alert. Security zones are promulgated by Captains of the Port or District Commanders. These routine and frequent rulemakings support the Coast Guard's broad roles and responsibilities of maritime security, safety, and stewardship. The total number of actions expected is 100 annually.