Many other passengers could smell the gas, said Diao.
"It was dangerous since not only the train was fairly crowded at that time, but there were also children not far from the gas canister," he said, adding that the man finally disembarked at Dongdan Subway Station.
Passengers should be willing to cooperate with the security checks, since their safety is at stake, said Diao.
"If passengers can bring [dangerous] things like gas canisters on board the train without being stopped, then all our efforts to support these security checks are meaningless," he said.
An anonymous police officer from Huixinxijiebeikou Subway Station said that dangerous articles, including knives and toxic or flammable liquids are prohibited.
"Gas canisters are absolutely prohibited as well," he said, adding that police did detain people who were found with banned items on the subway.
"But the numbers we detain are much lower these days," he said, although he did not give figures, or say why the numbers had dropped.
Wang Hongwei, professor of the School of Public Administration and Policy of Renmin University of China, told the Global Times that the security check system on the Beijing subway is not as reliable as it should be.
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