PVC Cable Burning Behaviour and Intumescent Protection: Small-Scale Tests and the Browns Ferry Lesson

Abstract

Electrical cables are present in nearly every building and industrial site. In a fire they can act as the starting point, as a path along which flames travel, and as a major producer of smoke. This paper presents laboratory results for a single-core PVC-insulated copper cable and a literature review of passive fire protection (PFP), with attention to intumescent coatings. Two standard tests were run: vertical flame propagation under IEC 60332-1-2, and cone calorimetry at 40 kW/m² under ISO 5660-1. Both vertical specimens passed. Flames died out within 5 s of removing the burner, and charring reached only 80 mm and 160 mm along a 600 mm length. In the cone calorimeter the insulation ignited at 125 s, peaked at 114.89 kW/m², gave a total heat release of 70.81 MJ/m² and a smoke production rate of 0.175 m²/s. The material therefore shrugs off a small flame but, under sustained radiant heating, becomes a long-lived source of heat and smoke. The review part explains how intumescent coatings function, the product families available, how they fail, and how the 1975 Browns Ferry fire reshaped cable-protection rules.

Introduction

The text examines the fire risks associated with electrical cables, their ignition and flame-spread behaviour, and the role of passive fire protection, particularly intumescent coatings, in preventing the spread of cable fires. It highlights that cables are often overlooked in building fire safety, despite being a significant potential source and pathway for fire. Cable fires may originate from damaged insulation, overheating, electrical faults, overloaded circuits, loose connections or exposure to external fires. Because cables often run continuously through trays, shafts and service galleries, fire can spread rapidly from one cable to another, creating serious risks to buildings, equipment and human life.

The review explains how cable construction and insulation materials influence fire behaviour. Copper and aluminium are common conductor materials, while PVC, XLPE and LSZH are widely used insulation or sheath materials. PVC can melt, drip and produce dense smoke and toxic hydrogen chloride gas. XLPE tends to form char rather than melt, while LSZH materials are designed to produce less smoke and almost no halogen acid gases. The text also explains three principal routes to cable ignition: external heating, heat transferred from a hot conductor or faulty connection, and Joule heating caused by electrical overload or short circuits. Flame propagation depends on insulation properties, conductor material, cable arrangement, orientation and surrounding airflow.

The study includes experimental investigations conducted at the National Fire Service College, Nagpur, in September 2026. A single-core PVC-insulated copper cable with a diameter of 12.5 mm was selected for testing. Two standard experimental methods were used:

1. Vertical Flame Propagation Test (IEC 60332-1-2): This test examined whether the cable continued to propagate flames after exposure to a standardised propane-air flame. Both specimens passed the test, with damaged lengths of 80 mm and 160 mm, respectively.

2. Cone Calorimeter Test (ISO 5660-1): This test was designed to assess the heat release, mass loss, smoke production and carbon monoxide emissions of PVC cable material under an external heat flux of 40 kW/m².

The review also focuses on passive fire protection systems, particularly intumescent coatings. These coatings expand when exposed to high temperatures, forming an insulating protective char layer that reduces heat transfer to the underlying cable and delays ignition and flame propagation. Their effectiveness depends on their composition, application, thickness, durability and maintenance. The text also acknowledges potential hazards and limitations associated with coating materials and their long-term performance.

The 1975 Browns Ferry fire is presented as an important case study demonstrating the consequences of inadequate cable fire protection and the importance of effective passive fire barriers and compartmentation. It illustrates how cable fires can spread through interconnected cable systems and disrupt critical electrical and safety functions.

The study further identifies limitations in the experimental programme. Only one type of PVC-insulated copper cable was tested, and the investigations were limited to small-scale experiments. Large-scale cable tray tests, ageing studies and experimental evaluations of intumescent-coated cables were not conducted. These areas are recommended for future research.

Conclusion

1) The PVC cable passed the IEC 60332-1-2 vertical flame test. Residual flame lasted no more than 5 s and damage was limited to 80 mm and 160 mm of a 600 mm specimen. 2) At 40 kW/m² in the cone calorimeter the PVC ignited at 125 s, peaked at 114.89 kW/m², released 70.81 MJ/m², lost 3870 g/m² of mass and burned for about 29 minutes, with a smoke production rate of 0.175 m²/s and a clear CO peak. 3) PVC is hard to ignite with a small flame but is a long-lasting source of heat, smoke and CO under sustained heating. In confined cable galleries this supports passive protection, low-smoke halogen-free cable, or both. 4) Intumescent coatings protect by swelling into an insulating char. Their performance depends on type, thickness, adhesion and ageing, and they are vulnerable to moisture, cracking and fires harsher than those they were certified for. 5) Browns Ferry shows that one combustible penetration seal can undo an otherwise sound design, and that protection must be properly rated and tested at full scale. Cable fire safety is a joint problem of materials, electrical design, fire dynamics and regulation. Passive protection should match the real fire exposure, be installed with care, and be inspected throughout the life of the facility, with detection and suppression working alongside it.

References

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Copyright

Copyright © 2026 Dr. A. R. Sontake, Harsh Chaurasiya , Atharv Tivale, Kamlesh Kumar Yadav , Aditya Diwate, Sanjay M.. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.