Supplementary reading I 325

АН scaffolders in Hong Kong are required to wear safety harnesses, fall arrestors and independent lifelines. Scaffolds must also be inspected by a competent person — a CITA trade test holder with at least 10 years' experience — every 2 weeks and more often during tropical cyclones and strong monsoons. The main contractor's full-time supervisor should also inspect the integrity of the scaffolds regularly and record findings in stipulated forms.

Despite the training and skill of Hong Kong's bamboo scaffolders and the government's associated code and guidelines, serious accidents continue to occur, mostly in truss-out bamboo scaffolds. The overall accident rate in Hong Kong's construction industry in the past few years is around 60 for every 1000 workers. A total of 3835 accident cases were recorded in 2004, 3548 in 2005 and 3129 (projected) in 2006. The numbers of fatal accidents during these years are 17, 25 and 17 respectively. Repair and maintenance projects account for the majority of the accidents. Nearly half of the fatal accidents are grouped under "fall of person from height" involving truss-out bamboo scaffolds, unfenced edges, ladders and so on.

Many of the accidents in truss-out bamboo scaffolds have resulted from failures of the support bracket anchor bolts. The difficulty in fixing the anchor bolts from inside the building is cited as a major cause. Inadequacy of secure fixtures of lifelines to anchorage points has also been noted in many cases. Industry, institutions and government departments are working together in addressing the problem.

Metal versus bamboo.

Unlike metal scaffold poles, bamboo poles do not need oiling, painting or covered storage. They are much lighter and easier to handle, leading to fast erection: one worker can erect 75-100 m² of double-layered bamboo scaffolding a day, some 6—8 times faster than for a similar metal scaffold. Also, the cost of bamboo poles is only about 6% of the cost of steel poles.

Bamboo scaffolds are generally split into 15 m tall frames with those above ground level supported by steel brackets fixed to the main structure. The heavier weight of metal scaffolding means that vertical loads are usually taken all the way down to the base. This is

workable for medium-rise buildings but for a multi-storey building of, say, 124 m height, it is estimated that standards will be required in groups of three at base with double at intermediate levels. Intermediate steel brackets, if designed, would also be massive. In Hong Kong, where high-rise buildings are a norm and many urban sites are bounded by busy streets, shopping arcades and pedestrian bridges, treble and double metal scaffolds would not be practical.

Bamboo also has a much lower carbon footprint than metal. For Hong Kong it is cultivated in the neighbouring Guangxi province in abundance, and then transported to Hong Kong along the Pearl River simply by lashing the poles together and floating them downstream. Depending on the type of scaffolding, bamboo poles can be reused three to five times.

A city of old and new.

Hong Kong is a forward-looking city but one which also values its traditions and customs. For example, century-old tramcars pass slowly through the heart of the central district while state-of-the-art mass-transit trains speed through tunnels below and traditional dim-sum restaurants sit alongside the latest fast-food outlets.

(New Civil Engineer International, March, 2009)

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TAPESCRIPTS

• TAPESCRIPT 1A