Subway operator challenged
The operator of Beijing's subway system said yesterday that the escalator that suddenly reversed at a station on Line 4 on Tuesday, killing a 13-year-old boy and injuring 30 people, was a heavy-duty model, as were the other escalators used at the capital's subway stations.
But specifications provided by the company tell a different story, according to some mainland transport experts. They show the escalators are not built for heavy loads, can't cope with rush-hour passenger flows and their operation poses serious safety risks.
Beijing Metro Construction and Administration Corporation issued a statement on the website of the municipal Transportation Commission yesterday, denying a report in the South China Morning Post on Wednesday that the use of light-duty escalators was widespread in subway stations on the mainland. The company said that such a problem did not exist in Beijing.
'Our company has purchased heavy-duty escalators for Beijing Subway Line 4 and other subway lines,' it said. 'Escalators on Line 4 underwent heavy load testing when the line's construction was completed, and passed.'
To meet national standards, experts said, escalators would have to be able to endure heavy loads for half an hour in any three hours. In other words, if the rush hour began at 7am and ended at 10am, escalators could not be fully loaded for more than 30 minutes, otherwise their normal operation and the effectiveness of their safety mechanisms could fail.
Transport experts said that the capacity should be at least double to meet the continuous and massive flow of passenger traffic in subway stations, warning that running escalators beyond their designed capacity could cause the entire system to fail, as the many sudden reversals on the mainland had demonstrated.
Rao Meiwan, an escalator engineer at the Guangzhou Metro Design and Research Institute, wrote in a 2008 paper in the mainland academic magazine Urban Rapid Rail Transit that the mainland's national standard did not include a definition for heavy-duty escalators. That meant that subway builders were free to decide for themselves.
The half-hour heavy load benchmark was the national standard for ordinary escalators in public areas. It was not heavy duty, Rao wrote.
'For heavy-duty escalators, one hour of persistent heavy load in any three hours must be considered,' she wrote. 'The peaks of passenger flow mostly occur during rush hours. At rush hour, the interval between subway trains is two minutes, forcing the escalator to run almost continuously at full capacity.'
Fang Jin, an associate professor at Beijing Jiaotong University's school of electrical engineering, said yesterday that running escalators so far beyond their designed capacity was a crime against the public because of the danger this posed.
He said the motor would overheat, which could melt the insulation layers of wires and cause a short circuit that could punch a hole in a circuit board. Because that was where the escalator's 'brain' was located, severe malfunctions like sudden reversals could then occur.
Li Lianghua , a special equipment safety inspector at Beijing's Quality and Technical Supervision Bureau, told the Beijing Daily yesterday that investigators had found that none of the escalator's protection mechanisms had been activated before Tuesday's sudden reversal.
Manufacturer Otis declined to release details of the escalator model and specifications yesterday. Beijing halted the operation of all Otis escalators following Tuesday's accident. Tianjin followed suit yesterday.