October_1970 — Page 13

very smooth marble like result, and 'fair-faced' with the concrete cast in timber formwork, giving a board-mark- ed finish.

In all cases, these columns are left unfinished to cut down on maintenan- ce costs. The flat slabs appear as 15 in. deep but are in fact sealed coffer slabs, consisting of a 3 in. thick upper slab, a layer of 11 in. deep timber boxes. spaced in both directions by reinforc- ed ribs, and a precast 1 in. thick tile sealing the underside.

Where false ceilings occur, the tiles are omitted and the boxes removed after casting. Staircase and lift walls are reinforced concrete to provide stiffness.

The flat roof slab is cast in water- proof concrete and finished with a layer of heavy duty waterproof screed. This is then insulated by a 6 in. layer of consolidated earth, which has proved effective against temperature variations.

Walls to the therapy machine area

vary in thickness from 4 in. to 6 ft. 4 in. reinforced concrete and the con- crete mix varies from the standard 1:2:4 mix to a special barium concrete mix for the Betatron room walls and roof. Some 880 tons of baryte aggre- gate were imported to manufacture this concrete.

Special metal forms had to be fabricated to construct the thick walls in two skins, leaving a 2 in. gap in the centre, later filled with asphalt to con- tain the radiation. The floor slabs, machine pits and some walls in the megavoltage areas were cast in water- proof concrete without tanking.

Non-structural concrete sunbreak- ers of various types have been placed on the faces of the building to suit the orientation and act also as rainbreakers in time of storms.

Services

All internal walls are non-structural screens of hollow concrete blocks, finished with plaster or tiling. Floors

are generally 1 ft. square terrazzo tiles.

The air-conditioning system oper- ates on a central chilled water supply, circulating to the centre from the central refrigeration unit serving the whole hospital complex. The office areas, clinics and first class ward are designed for normal comfort con- ditions of 75 F and 55 per cent RH, with 75 per cent recirculation.

The megavoltage, deep therapy and isotope areas required special consider- ation in view of radiation hazards and the necessity for constant temperature of 75 F and a humidity of 50 per cent RH or less. Each of the therapy rooms was therefore provided with a separate unit, complete with all controls, and the Betatron unit operates on 100 per cent exhaust to atmosphere. The fume cupboards in the isotope laboratories also exhaust to atmosphere at high level.

One problem that had to be solv- ed was the cooling system for the Betatron machine, since the cooling

Far East BUILDER, October 1970

View from south-east

13