It is important to note that the deluge functioned to protect the launch vehicle from sound vibrational damage, not the pad.
You're thinking of hypergolic propellants like hydrazine and nitric acid. This is kerosene (RP-1) and liquid oxygen. Not particularly toxic, just hot as hell.
The deluge system in shuttle launches was for the flame trench and sound dampening to avoid the air pressure from the noise damaging the vehicle, not fire extinguishing.
You can see the launch tower get charred black, that's the fire protective paint.
It's not really possible to fight rocket fuel fires, just mitigate the damage.
It'd certainly suck to be one of the people who's slaved over the satellite for the last couple of years, to see your baby get blown to smithereens like this.