Are you obliged to keep all grass within the airport perimeters in a condition, which allows heavy vehicles to use it without getting stuck? Would not be an easy task in the tropics...
Changi has drains on the grass perimeter.
No but Panthers/Strikers are off-road capable. Looking at Google Earth terrain at SIN looks relatively flat.
I don't think there is any airport in the world without uneven terrain and water bodies within the perimeter.
It is kind of strange most vehicles formed one pavement hugging relatively slow beeline on a winding scenic route. Not one attempted to take shortest path. Most vehicles ended up one side of the fire.
These was also hesitation to move closer to the fire, these are what 60 meter spray capable trucks.
Crew didn't request for assistance, probably one of the reasons.