When there is a risk of a hazardous-materials spill during a school bus evacuation, how far upwind of the bus should the driver lead students?

AAMVA CDL Manual, Section 10.3.2 (Evacuation Procedures), p. 10-6

Hazardous-materials spills carry a wider danger radius than fire or debris because toxic vapors can travel and concentrate downwind. The extended 300-foot distance reflects that greater risk and is a distinct, testable figure from the general 100-foot rule.