AMPD is defined as the Average Most Probable Discharge of the lesser of 50 barrels of oil or 1 percent of the cargo from the vessel during cargo oil transfer operations to or from the vessel or a discharge of the lesser of 50 barrels of oil or 1 percent of the volume of the worse-case discharge for a facility OPA 90 requires that a containment boom equal to twice the length of the largest vessel involved in the transfer be deployed at the site of the operation within one hour of detection of a spill; additionally, skimmers and temporary storage must be on site within 2 hours.