 Intuitively, so long as they warn people to stay indoors while the waste is being removed, the city officials can legitimately remove the hazardous waste. This does expose some people to a risk of serious harm. But all available alternatives are worse: the waste cannot be left where it is, and evacuating the city is not feasible. A principle permitting officials to expose some people to a risk of harm in order to protect public health is one that no one can reasonably reject.