Accidents happen, but the unfolding chemical disaster in north-east China has prompted too many unanswered questions for the company responsible or the government to be allowed to sweep it under the carpet along with the countless environmental cata­strophes that have preceded it.

Why did it take more than a week for the 9m people of metropolitan Harbin - a city larger than most European capitals - to be told their drinking water was threatened by toxic benzene after an explosion at a PetroChina subsidiary's chemical plant in Jilin, higher up the Songhua river, on November 13?