INDUSTRIAL safety concern groups have called on the Government to ban a popular construction method on building sites, given the escalating accident rate. The general secretary of Association for the Rights of Industrial Accident Victims, Mr Chan Kam-hong, said the use of hand-dug caissons led to about 300 accidents each year. He said there was an average of two deaths a year as a result of these accidents and, this year, one worker had already been killed while working on a caisson. Hand-dug caissons have been a popular method to consolidate the foundation of a construction by opening a small-diameter hole and sending workers down to manually dig and lay concrete. Mr Chan said it was a popular method compared to mechanical alternatives, like piling or bore-piling, which were more expensive. The number of accidents was consistent even though the number of construction projects was falling, Mr Chan said. The president of the Society of Registered Safety Officers, Mr Lee Hung-kwong, said caisson hazards included the presence of methane gas, a sudden in-rush of water and earth, and metal buckets falling from above. Mr Chan said work in hand-dug caissons could also lead to a fatal lung disease - silicosis - caused by the inhalation of metal dust particles in the manholes. He said about 150 construction site workers, the majority of them working in caissons, suffered from silicosis every year. Mr Lee said: ''If this method of work is not to be stopped, we expect Hongkong will continue to register silicosis, deaths and bodily injuries among caisson workers.'' The Housing Authority this month stopped using the method on its construction sites, out of concern for workmen's health and safety. The Works Branch has proposed a ban on hand-dug caissons in construction projects by the Civil Engineering, Drainage Services, Architectural Services and Water Supplies departments. However, the ban would not cover work on steep hillsides, where using manual workers to dig the holes is believed to be safer than using machinery. But Mr Chan said: ''There should be legislation to ban hand-dug caissons completely as they can be replaced by using machinery even on steep hillsides or small sites.'' The concern groups said the voluntary participation of private developers and public bodies like the Provincial Airport Authority was important. ''If the architects or engineers wish to exclude such method of work, the contractors engaged on foundation work will then follow,'' Mr Lee said. Mr Chan said caisson workers could switch to handling more technically advanced methods like bore-piling which was safer and needed a greater workforce. The deputy convenor of Legco's lands and works panel, Mr Samuel Wong Ping-wai, agreed that caissons should be banned but said drafting a new regulation under the Buildings Ordinance was enough to exercise control.