A “fog flashover” caused by trapped soot particles on a section of the Beijing-Guangzhou railway led to a one-hour outage of the system on Wednesday afternoon. The incident took place as the G513 bullet train, which was en-route from Beijing, arrived in Xinyang East, Wuhan in central China's Hubei province. Operations were delayed for nearly an hour, according to the Wuhan Evening News . The Wuhan Railway Bureau released a statement later in the afternoon that said the accident was caused by haze. Passengers posted on Sina Weibo that they had heard a loud explosion and seen sparks before the train came to a halt. Fog flashovers, also known as “dirty flashes”, are short-circuits caused by fog-induced moisture or soot build-up on the surface of electrical equipment. They are a common problem for railway operators everywhere but can be avoided by regular cleaning and installation of high-speed current breakers.