The first rain that hit Tianjin on Tuesday after the deadly blast raised more concerns as the streets were covered with white foam and local residents who came in contact with the rainwater complained of 'stinging sensation' and rashes.

Residents told local media that those who got wet in the rain experienced a burning sensation on their face and lips, while others reported a stinging sensation on their arms, according to a NetEase News report.

Chinese meteorological experts have, however, assured the residents that the rainfall would no longer pose a direct threat to people's health, CCTV News reported. But people are worried that the rainfall could spread harmful chemicals such as hydrogen cyanide across the city.

During a news conference on 18 August, Bao Jingling, the chief engineer of the Tianjin Environmental Protection Bureau warned local residents against exposing themselves to rain due to the presence of dangerous sodium cyanide at the blast site. "If the dust (from sodium cyanide) is mixed with water, it triggers the formation of hydrogen cyanide, a colourless and highly poisonous liquid that becomes a vapour at even slightly above the room temperature," he had said.

"In particular, people should avoid spilling water on the dust," he added.

Chemical experts in Tianjin, after taking 29 water samples from the blast site, found that sodium cyanide was present in all of them. In one place, it was found to be 28 times beyond the permitted limit.