During a lull between air raid warnings earlier this month, Iryna Nikolaieva sat in a stairwell of a Kyiv bomb shelter where she had been living for three days and called engineers at two chemical plants near the front lines in the country’s east. Nikolaiva worked as an expert on hazardous waste, and she worried that fighting near the facilities could damage earthen dams holding back hundreds of thousands of tons of chemical sludge, setting off a catastrophic accident.