Role of fire-resistant cables in critical firefighting systems: a comprehensive review

Understanding life-safety and firefighting ‘wiring systems’ is essential, and several countries have now upgraded the testing of fire-resistant cables and wiring systems to adopt and harmonise with a more realistic standard time temperature curve. The logic behind this is that ‘essential’ circuits must at least survive the same fire intensity as all the other fire-rated components, elements and systems of the building exposed to the same fire.

The reliability of electric cables during a fire is crucial for life safety, firefighting and critical emergency systems. If these essential cable systems were to fail, the vital equipment they power would also fail, endangering the lives of occupants, emergency responders and property.

Building regulations frequently stipulate that emergency equipment must maintain operation for the duration necessary to fulfil its intended purpose. There is a widespread expectation that these ‘systems’ should be both suitable for their intended function and in compliance with the minimum code requirements. This article explores how the current BS and IEC cable testing methods can satisfy this requirement.

Building codes and regulation

Numerous fire-code requirements concerning essential cables primarily revolve around the product’s testing and performance criteria, which are incorporated into Building Codes and upheld by regulatory authorities. Certification bodies in many countries audit, test and then certify companies and their fire-performance cable products to specific performance standards on a ‘component only’ basis. This does not validate or imply any ‘installed system performance’ or ‘fitness for purpose’. 

To ensure the validation of an entire system, including all its components and installation methods, it is essential not only to subject them to joint testing and certification but also to ensure that the whole system complies with local regulations during the installation phase with the continuing focus on building safety, fire-resistant cables – and their ability to service critical systems in the event of a fire. 

So, the cable shall be suitably chosen and installed; fire-resistant cables must comply with the following codes of practice:

• BS 5266-1: Emergency lighting – Code of practice for emergency escape lighting in premises.
• BS 5839-1: Fire detection and fire alarm systems for buildings – Code of practice for the design, installation, commissioning, and maintenance of systems in non-domestic premises.
• BS 8519:2010: Code of practice for the selection and installation of fire-resistant power and control cable systems for life safety and fire-fighting applications.

Upgraded fire classification

We know that fire is a dynamic force, exhibiting movement, expansion and altering the shape, size and characteristics of everything it encounters. To simulate real fire scenarios accurately, it is essential for testing to encompass factors like the risk of flashover, falling debris during a fire (including potential impact on cables), and exposure to water, either from sprinkler systems or fire hoses.

British Standards offer exemplary test scenarios that illustrate this approach. For instance, BS 8519 (applied to cables exceeding 20mm) mandates direct impact testing and high-pressure water-jet tests on a single sample. Another example is BS 6387 CWZ (relevant for cables under 20mm), which requires a three-hour fire test, simulating situations where residents may be trapped in a tall building. In such scenarios, critical safety equipment might need to operate for extended periods, irrespective of size or construction. Each cable sample must pass a realistic fire scenario test to ensure reliability.

Many polymeric cable’ insulation and sheath materials can deteriorate rapidly when exposed to high temperatures. Consequently, the enhanced classification of fire-rated cables is pivotal in the integrity of critical firefighting systems.

Types of fire and flammability testing  

• Flame spread: This test focuses on assessing a product or material’s reaction to fire in controlled environments, where specific parameters such as temperature, airflow, or pressure can influence the fire’s propagation. For instance, a cable may undergo testing to determine whether it emits particles that contribute to the fire’s spread.
• Fire resistance: This test concentrates on how effective the product is at enduring a fire and continuing to operate in a fire scenario. Products often tested for fire resistance are designed for withstanding fire for an extended period, such as 120 minutes for a fire-resistant cable.

Fire resistance performance (insulation integrity tests)

BS 6387, BS 8491, BS EN 50200, BS 8434-2 & IEC 60331-1,2&3, IEC 60331-21,23&25

Both British and IEC standards for fire-resistant cable testing do not necessitate the installation of cables on supports or with common fixing components, distances or methods used during typical installations. Test specimens are typically configured horizontally with short laboratory-scale cable lengths. The test flame source typically involves 500mm- or 600mm-long ribbon burners with a flame temperature specified in the test standard. Depending on the cable’s construction, the insulation is usually safeguarded by an outer sheath, which can be copper, steel wire-armoured, or a fire-resistant polymeric sheath, each responding differently to fire conditions.

To meet the requirements of a fire-resistant cable, the construction must align with the appropriate British Standard tailored to the specific type of fire-resistant cable. Several references for cable fire performance exist, including BS 50200, BS 8434, BS 8491, BS 8519, BS 6387 and IEC 60331. These standards specify variations in time and temperature at which cables are tested under different fire conditions, ranging from a 30-minute rated cable tested at 830°C (e.g. PH30 cable as per BS EN 50200) to a three-hour rated cable tested at 940°C (BS 6387 category C). These standards collectively offer confidence to those specifying the cable that it will continue functioning in the event of a fire.

Fire propagation performance (fire spread & flame retardance)

This test ensures the fire behaviour of flame-retardant material prevents flame propagation during a fire emergency. When the material comes into contact with fire, the by-product from the endothermic reaction is gaseous water, which will help envelop the flame and thereby exclude oxygen from the fire.

The best flame-retardant cables are often halogenated because the insulation and outer jacket are flame-retardant. Still, when we need halogen-free cables, we often find only the flame-retardant outer jacket and the inner insulation, which are not. This has significance because cables with a flame-retardant outer jacket may pass flame retardance tests with an external flame source (BS EN 60332-1, BS EN 60332-3). Designers and users of cables claiming must meet to be flame retardant to IEC 60332-3-22/23/24/25.

The primary importance of fire load

Many countries worldwide are moving to greater use of Halogen Free and Flame Retardant (HFFR) cables to increase building safety. To provide halogen-free cables, cable manufacturers often choose polymers like polyethylene (sometimes referred to as polyethene) (PE & XLPE) because it is easy to process and cheap; however, although PE is halogen-free, it has a naturally high fire load.

The table below compares the fire load in MJ/Kg for commonly used cable-insulating materials. While the Heat Release Rate and volatility in the air may vary among these materials, the amount of fuel introduced to a fire per kilogram and the resulting volume of heat produced and oxygen consumed can be assessed comparatively. For instance, the heat release for Petrol is 48MJ/Kg, Coal is 25MJ/Kg, and Wood is 18.5MJ/Kg.

Smoke emissions 

The first and most crucial aspect of smoke is how much smoke is released. Typically, the larger the fire, the more smoke is generated. So, whatever can be done to reduce the spread of fire will also correspondingly reduce the amount of smoke.

Most fire-resistant cables rely on polymers or tapes to increase their resistance to fire, yet these materials can burn away at as little as 80°C, exposing the critical conductors. To give some soft-skinned polymer cables flame-retardant properties, halogens such as chlorine, bromine and fluorine are added to the outer sheath. When exposed to a fire, these halogenated polymers will release extremely toxic halides. This smoke restricts breathing and increases the risk of inhaling when following the common rules during a fire. 

Low-smoke, zero-halogen (LSZH) flame retardant (FRT) cables comply with IEC 60332, IEC 60754 and IEC 61034, which ensure that the flame-retardant cables reduce flame propagation, prevent the release of toxic gases and control smoke emission under fire conditions.

Ensuring a safer and more sustainable future together

As the complexity of new buildings increases, decision-makers in the supply chain must ensure that specified products meet safety standards and compliance requirements, adhering to recognized governance and regulations. The rise in high-rise building fires globally has emphasized the importance of product quality, especially for fire performance circuits.

The latest generation of fire performance cabling guarantees the continued operation of critical fire-safety circuits for a minimum of 30 minutes, extending up to 120 minutes during a fire. In establishments like hospitals, schools, shopping malls and airports, which often feature intricate addressable-loop fire-alarm systems, the choice of cabling becomes crucial.

Recognizing this, industry experts and regulators are advocating for more rigorous testing standards. An upgraded classification of fire survival cables has been introduced for critical systems, enabling them to power essential circuits during a fire and withstand the challenges posed by safety systems, including falling debris, collapsing walls, fire hoses, high-pressure sprinklers and smoke extraction.

While fire survival cables play a crucial role in building safety, there is a lack of understanding about their significance, prompting local regulatory authorities to educate the market on the advantages of specifying these cables. There can be no compromise, and thorough fire-performance testing of cables is essential due to its numerous benefits. Equally important is understanding the correct installation procedures for these cables.

About the Author

Manikandan Annadurai

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Manikandan Annadurai is a Reaction-to-Fire Testing Engineer with Dubai Civil Defense’s Emirates Safety Laboratory. Manikandan is a Chemist and has 18+ years of various industrial experience including Fire Testing, specializing in designing and conducting comprehensive fire tests to evaluate the performance of materials under different conditions.

• Manikandan Annadurai

  Fire performance testing on electric cables/wires