I just had one break out, and the requirements for the HazMat garage are enormously expensive. Is this the only way to quench those special flames?
Yes. This is the only way to put out HazMat fires. Even though the requirements are quite expensive, there is good news...
Getting a university and the appropriate school is certainly a grind, but it's a grind you'll only need to do once per region.
The best thing to do with regards to industry prior to being able to extinguish HazMat fires is to keep the density down by lowering the density capacity of the connected streets in the zone. I have found that these fires can happen quite often if you don't have the HazMat garage, and when they do, they will repeatedly knock out very large factories and lose you quite a bit of tax income while they rebuild and restaff.