Intended to cover the best existing practice at the time it was written and not to extend the boundaries of technology. For this reason the scope of vessels under pressure is limited to moderate pressures and sizes, although no sizes limits have been placed on tanks subject only to hydrostatic head of liquid content. These limitations are, however, not intended to inhibit development. With agreement between purchaser, manufacturer and inspecting authority, vessels for use beyond the present limits may be designed and constructed in accordance with the principles of the standard.

BS 4994(1987) : 1987