Fire behaviour of cables and electric conductors

The fire behavior of cables is essential to the fire safety of modern infrastructures. In the event of fire, cables can spread rapidly and release toxic fumes, complicating evacuation and rescue operations. What's more, these cables may have essential functionality that needs to be preserved for as long as possible. This applies not only to power, control and communication cables, but also to optical fibers. Understanding and controlling this behavior is therefore crucial to minimizing risks and protecting human life and property.

When a fire breaks out, the ambient temperature rises rapidly, leading to the thermal decomposition of wiring materials. This decomposition releases flammable gases, which ignite and contribute to the spread of the fire. Polymer cables give off dense, toxic fumes, making it difficult to evacuate occupants and rescue services. What's more, due to their functionality and geometry, cables allow fire to spread vertically and horizontally, particularly through walls. The phenomenology of cable fires therefore includes ignition, flame propagation and the emission of heat, smoke and toxic combustion products, as well as interaction with various systems such as bushing caulking.

Two key concepts in the study of cable fire behavior are reaction to fire and resistance to fire. Reaction to fire refers to a material's ability to contribute to the ignition and spread of fire. Cables can be classified according to their flammability, the speed at which flames spread, and the amount of heat and smoke they emit. In Europe, the classification of cables in terms of reaction to fire is standardized by the Construction Products Regulation (CPR), which includes specific tests to assess these characteristics.

Fire resistance concerns the ability of a cable system to maintain its integrity and functions for a given period under fire conditions. This includes the ability to continue transmitting electricity or signals under extreme fire conditions, crucial for fire safety systems such as ventilation machinery, alarms and emergency lighting. It's important to differentiate between the fire behavior of cables alone and that of complete cable systems. A cable system integrates not only the cables, but also the cable trays, support and any additional protective devices (e.g. wrapping, dedicated channels, etc.). These components can have a significant influence on overall fire behavior. For example, a protected or encased cable tray can delay the onset of critical temperatures. Fire safety standards therefore take this complexity into account by requiring fire resistance tests on complete systems rather than on isolated cables.

The aim of this article is to provide an in-depth analysis of the fire behavior of electrical...