Gary Parker, Technical Manager for ECA, answers this key question.
More than ever, data communications and control cables are built into the fabric of our homes and offices, alongside traditional power cables. However, with more connectivity, there comes a larger amount of containment along which a fire could spread. This is important as data comms, power and control cables come under the CPR, designed to consider the reaction of cables within a fire.
ABCs for CPR
The CPR covers all construction products and classifies them by their reaction to fire. It is also the reason behind the CE marks seen on many construction products. To keep up with the new ways cables in buildings are made, installed, used and maintained, the CPR was updated and became a legal requirement in 2017. This development was met with some confusion, particularly over the new European Classification (or EuroClass) system which replaced the old Construction Products Directive (CPD).
An obvious benefit of the CPR is that it enables designers, specifiers and other industry professionals, as well as consumers, to compare the safety performance of products that may have come from different manufacturers. In other words, it allows easy like-for-like comparison between products.
Stopping fire in its tracks
Government statistics between 2017-18 show that, in England, almost 31,000 fires involving fatalities, casualties or rescues occurred in homes, and over 15,000 occurred in other buildings (offices, shops, hospitals, schools, etc.). In approximately 7% of these fires (around 3,400 fires), wiring insulation was identified as the main material responsible for it propagating.
Clearly, the type of cable installed, and the way it reacts to fire, is a critical consideration for designers and installers. The same statistics also concluded that “the most commonly identified cause of death from a fire incident is being overcome by gas or smoke.” Data communications cables currently available in the UK are insulated, bedded or sheathed with materials such as PVC, TPE, Nylon, metal weaving and mercerised cotton. Each reacts differently to fire and will have a different EuroClass rating.
PVC, one of the more commonly found materials in buildings, has been used to insulate a variety of cables since the 1950s. In the event of a fire, it produces highly toxic black smoke and acidic gases. It also acts as a fuel, helping to propel flames along a cable and through a building and its voids. This danger is further exacerbated by falling flaming droplets caused by melting. The smoke and gases given off by burning cables can hinder a building’s occupants from escaping a building in event of a fire. It can also inhibit firefighters by blocking their vision and reducing the effectiveness of emergency lighting.
Another less immediately obvious side effect of acidic gases may be corrosion of other metallic components – often within electrical and electronic equipment. To fully understand the CPR and EuroClass, it’s important to make the distinction between two similar but separate properties of cables when exposed to fire.
- Reaction to fire – this describes a cable’s behaviour during combustion, as well as how it might contribute to developing or spreading a fire.
- Resistance to fire – this describes a cable’s ability to continue operating as normal (that is, to maintain a circuit’s integrity) during a fire. This is often referred to as ‘fire survival’.
The CPR only relates to the first characteristic described above – a cable’s reaction to fire. At the time of writing, the CPR in terms of cables and their resistance to fire remains under review. It will likely be a long time before this comes into effect.
Top of the class
Under the CPR, European Classification replaces IEC 60332-1-2:2004, which was the previous benchmark for assessing the flammability of cables. Since methods of testing cables have changed drastically, direct comparisons to the old standard are not exactly straightforward. The table below clarifies the classes:
Some readers may notice that these seven classes broadly align with classes A to F used for other construction products, and which are already referred to in UK Building Regulations. It is clear that a cable in class Aca would be the best in terms of fire performance, and an Eca cable would be seen as the worst. Class Fca cables should be used with caution or avoided entirely if possible, as it would be of unknown origin with no identification markings or labelling.
For more information, visit: https://eca.co.uk/