Derivation of Metocean Design and Operating Considerations Gives general requirements for the dete rmination and use of meteorological and oceanographic (metocean) condit ions for the design, construction and operation of offshore structures of all types used in the petroleum and natural gas industries. The requirements are divided into two broad types: • those that relate to the determinat ion of environmental conditions in general, together with the metocean parameters that are required to adequately describe them; • those that relate to the characterization and use of metocean parameters for the design, the construction activi ties or the operation of offshore structures. The environmental conditions and me tocean parameters discussed are: • extreme and abnormal values of me tocean parameters that recur with given return periods that are consider ably longer than the design service life of the structure; • long - term distributions of metoce an parameters, in the form of cumulative, conditional, marginal or joint statistics of metocean parameters; and normal environmental conditions that are expected to occur frequently during the design service life of the structure. Metocean parameters are applicable to:• the determination of actions fo r the design of new structures; • the determination of actions for th e assessment of existing structures; • the site - specific assessment of mobile offshore units;• the determination of limiting enviro nmental conditions, weather windows, actions and action effects for pre - service and post - service situations (i.e. fabrication, transportation and insta llation or decommissioning and removal of a structure); and facility operations, where appropriate