New single storey platform enclosure to boiler house upper roof (Level 6) and structural skeleton frame from ground level. Alterations to the east elevation of boiler house plant room at Level 2 to enlarge existing external wall opening. Demolition of existing Level 2 gantry platform and construction of new enlarged gantry platform. Proposed cantilevered extension to existing sampling room enclosure at Level 5. New access stair from Level 5.