A tanker spill has occurred near the bus, but the material is outside and students would have to walk through a vapor area to leave. What principle should guide the evacuation decision?

1. Sometimes it may be safer to remain on the bus rather than expose students to hazardous material contact
2. Always evacuate through the spill, regardless of exposure
3. Always send two students first to test whether the material is dangerous
4. Ignore the spill if the bus engine still runs