Some residents and journalists near the blast site in Tianjin experienced skin burns as rain hit the Binhai New Area on Tuesday. Amid fears the rain could spark toxic reactions with chemicals at the site - in particular with hundreds of tonnes of sodium cyanide - an official urged the public to "stay far away". As the rain progressed, an unusual white foam emerged on roads near the blast site. A journalist for Caixin reported feeling burns on the lips and arms after being exposed to the rain. A volunteer relief worker posted on Weibo that contact with the rain turned the skin on her arms red and caused it to sting. Similar symptoms were reported by other journalists and volunteers, according to Tencent's news site. Symptoms were relieved by rinsing with water. But other people exposed to the rain, including South China Morning Post reporters, displayed no such symptoms. Tianjin's environmental authorities said pollution in air and water remained at safe levels. Read more: Tears as Tianjin mourns victims of warehouse blasts in commemoration ceremonies across city At least 3,000 tonnes of chemicals - including 700 tonnes of sodium cyanide - were in the warehouse where the two blasts occurred last Wednesday. Deng Xiaowen, director of Tianjin's environmental monitoring centre, said there had been no fluctuation in air quality at 17 monitoring spots after the rain. The white foam was "a normal phenomenon when rain falls, and similar things have occurred before", Deng said. Still, fears remained over the hundreds of tonnes of sodium cyanide that were at the core blast zone. The chemical can react with water to produce highly poisonous hydrogen cyanide gas. Bao Jingling, chief engineer of Tianjin Environmental Protection Bureau, said sewage treatment had been beefed up in the zone, and only treated water would be discharged. There would be urgent treatment of any cyanide pollution, he said, and air quality would be closely monitored with the public informed once pollution went above safe levels. Caijing magazine quoted him as saying that "the best way is to stay far away from the site, there is no other way". But some residents were not deterred. A homeowner whose flat was damaged in the blasts took part in an outdoor protest in the rain, demanding compensation. "Our homes have been destroyed, what more should we fear?" he said.