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        # Understanding Fire Safety Standards: UL 94 and IEC 60332 in PVC Compounding

        

**Topic:** Explainer

        

Meeting fire safety ratings like UL 94 V-0 or vertical flame propagation under IEC 60332 is a mandatory requirement for electrical conduits and cables. Using chlorine-donating secondary plasticizers like [NBT Diamond Grade NP CPW](/products/plasticizers/cpw-diamond) alongside antimony trioxide builds a synergistic flame-suppressing char.

        
        
        
        
        
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          ## Frequently Asked Questions

          
### How does CPW help PVC pass the vertical flame test?

NBT Diamond Grade CPW acts as a chlorine donor. When exposed to flame, it releases HCl gas which reacts synergistically with antimony trioxide to form antimony trichloride vapor, quenching the combustion radicals.

### What is the optimal ratio of antimony trioxide to chlorine?

The optimum chemical synergy is achieved at an Sb:Cl atomic ratio of approximately 1:3. In typical formulations, this corresponds to a weight ratio of 1 part antimony trioxide to 3-4 parts chlorinated paraffin wax.

### Why does flexible PVC burn faster than rigid PVC?

Rigid PVC contains ~57% chlorine and is highly self-extinguishing. Flexible PVC contains flammable hydrocarbon plasticizers (such as DOP or DOTP) which reduce the overall chlorine percentage and act as fuel, requiring flame-retardant additives.

### Can zinc borate replace antimony trioxide?

Zinc borate can replace a portion of antimony trioxide (typically 30-50%). It acts as a smoke suppressant and char-forming agent, reducing the total cost of the flame retardant system.

        
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By NBT Technical Desk · Updated 2026-07-04

        

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