Fail Safe, Fail Secure

There is a particularly harrowing article about the catastrophic train crash that occurred when two high-speed trains collided in Wenzhou, China on July 23, 2011. Evan Osnos’s article “Letter from China: Boss Rail – The disaster that exposed the underside of the boom,” which appeared in the October 22, 2012 issue of The New Yorker, describes in detail the natural events, faulty procedures and human error that led to the crash. From an engineer’s point of view, the following quote is of particular interest:

“At 7:30 PM … lightning struck a heavy metal box beside the tracks. The box … was part of a signal system that lets drivers and dispatchers know where trains are … When the lightning struck the box, it blew a fuse, which caused two catastrophic problems: it cut off communication and froze the [traffic] signal on the color green.”

The article goes on to describe the series of events, precipitated by the blowing of the fuse that resulted in a crash killing 40 people and injuring 192 others.

Later in the article we have the following explanation as to why the signal box was inadequate with respect to safety:

“According to investigators, the signal that failed … was developed over six months … [with] a staff of some thirteen hundred engineers … [The staff] was overwhelmed by demands … and those in charge of the signal performed only a ‘lax’ inspection, which ‘failed to discover grave flaws and major hidden dangers.’”

It may well be that testing of the signal box was inadequate, but it is also highly likely that the design and manufacture were also lacking.

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