If a vehicle carrying a Type B(U) flask is involved in a severe road collision but the flask remains undamaged, what must the driver check first regarding radiation safety?

1. Open the flask cover with a wrench to look inside
2. Roll the flask down an embankment to clear the road
3. Measure radiation levels around the vehicle using a calibrated radiation survey meter to confirm shielding integrity and verify no dose rate increase
4. Pour water over the flask surface