The detailed description from HB to 5VA is as follows ( UL94 ):
HB: slow burning on a horizontal specimen; burning rate <76 mm/min for thickness <3 mm or burning stops before 100 mm
V-2: burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
V-1: burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
5VB: burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may develop a hole.
5VA: Burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may not develop a hole.
Most of our products have reached V-0 and above standards. This is especially important in the selection of electrical pipes.
PVC is chemically resistant to acids, salts, bases, fats, and alcohols, making it resistant to the corrosive effects of sewage, that’s why it is so popular in sewer piping systems.
It is also resistant to some solvents, this, however, is reserved mainly for uPVC (unplasticized PVC). Plasticized PVC, also known as PVC-P, is in some cases less resistant to solvents. For example, PVC is resistant to fuel and some paint thinners. Some solvents may only swell it or deform it but not dissolve it, but some, like tetrahydrofuran or acetone, may damage it.
For more information, refer to Wikipedia about Chemical.