For the same reason you don’t put salt water in the radiator of your car.
Salt destroys metal, and it does it rather quickly.
Your fire fighting apparatus would become junk before you were done using it.
Joe, PLEASE re-read the latest article ten times real slow. Over 100 people dead and over 1,000 people missing and you worry over possible damage to a fire pumper truck???!!!
I run my 225hp Mercury engines in salt water and then wash them off good inside and out by running them in a fresh water lake. The Navy uses pumps to pump saltwater for fires.
A few firetrucks aren’t worth over 1,000 dead people including quite a few children I’m sure.