If you start using tankers, you have to evacuate everyone from the area (in a larger area than their current evacuation cordon). It would mean all other on-site

If you start using tankers, you have to evacuate everyone from the area (in a larger area than their current evacuation cordon). It would mean all other on-site firefighting operations would have to stop. Using aerial tankers would be unsafe (flying planes are very low altitudes through a city), and would result in a net reduction in firefighting efforts on scene.