Adam Franczak, TME
Power, control and communication cables have undoubtedly contributed to the spread of many fires due to their flammability and prevalence throughout buildings. Defective cabling can also be an ignition source. To improve success in evacuating burning buildings and quickly extinguishing fires, the European Union (EU) has added rules on cables to its Construction Products Regulations (CPR). These have applied since July 2017.
Past classifications used for cable jackets often concerned only the spread of flames, when in practice the emission of smoke and toxic chemicals from burning cables can be a greater danger. CPR draws all these factors into one standardised and more stringent regulatory system.
Compliance with CPR depends largely on moving from halogenated materials, such as PVC (polyvinyl chloride), to low smoke, zero halogen (LSZH) products (Figure 1). Alternative acronyms for LSZH include LSOH (low smoke, 0 halogen) and LSHF (low smoke, halogen free). These must not be confused with LSF (low smoke, fume) cables, which might contain halogens. Nor should it be assumed that all LSZH products are good at retarding flames.
There is much variation in product performance across all safety criteria, which is why CPR assigns cables to seven Euroclasses for flammability and to further subclasses for specific hazards. For buyer confidence, these product safety designations are backed by a verification system.
In reaction to fire, a standard PVC cable will emit dense black smoke. This makes it difficult for occupants to find an exit, or to breathe, and for firefighters to enter and search the building. LSZH cables produce less optically dense smoke, at a lower rate.
Halogenated cable materials contain elements such as chlorine, fluorine or bromine, whose combustion products can be toxic and corrosive. Hydrogen chloride gas, for instance, which dissolves in water to form hydrochloric acid, may burn respiratory surfaces, eyes and skin. Further risks include damage to electronic equipment and metal structures by acids.
With a rapid proliferation in the amount of cabling needed for data transmission and other modern applications, there is now potentially more fuel for fire than ever before. Extra caution is needed when numerous cables are close to people or sensitive machinery (Figure 2). Fire, smoke and toxic hazards are especially serious in situations where ventilation is poor and evacuation is difficult. Aircraft, ships, submarines, trains, airports, stations, multi-storey buildings, industrial premises and offices with confined spaces would all fit into this category.
Click image to enlarge
Figure 2: Bitner’s LSZH offering includes EB0080 cables for transmission of BUS signals in intelligent building management systems. Their sheath material is self-extinguishing and flame retardant.
Cable Euroclasses and assessment requirements
A simplified summary of CPR cable classification and its test requirements is given in Table 1. Reaction or contribution to fire is assessed in relation to specific European standards. It is unlikely that any cable will qualify for class Aca or Bca.
Click image to enlarge
Table 1. Simplified summary of CPR cable classification and its test requirements
Additional fire performance criteria are considered for classes B1ca to Eca:
· Smoke production – mandatory – scored as s1 (best – with possibility of further division into s1a and s1b), s2 (middle) or s3 (worst)
· Flaming droplets – optional – scored as d0 (none), d1 (few) or d2 (more than d1)
· Acidity – optional – scored as a1 (low), a2 (limited) or a3 (more than a2)
To achieve any Euroclass above Fca, testing must be carried out by an authorised laboratory designated as a ‘notified body’ by the European Commission. For classes B1ca, B2ca and Cca, the system also requires permanent production assessment by an appropriate unit. Tests to establish class Fca can be carried out by the manufacturer itself or by a laboratory of its choice. If the cable fails to qualify for class Eca, it is assigned to Fca.
It should be noted that additional testing and production auditing can be costly. In some cases, a manufacturer may accept a lower Euroclass ranking for a product which, if fully assessed, might have ranked higher.
What does the law demand from you?
CPR places demands on those who manufacture, import or sell cables for permanent use in domestic, commercial or industrial buildings and other civil engineering structures in the EU. It also applies to the installers and engineering companies who buy and use them.
Product assessment must be obtained and verified as summarised in the previous section. Cable packaging must show a CE (Conformité Européene) mark and a reference to the product’s Declaration of Performance (DoP). DoP documentation, containing the cable’s Euroclass, test details and other essential information, must be available on request. Manufacturers and importers must maintain records of cables sold, including their DoP, for up to ten years after sale.
At present, it is left to individual EU states to decide whether a minimum cable class should be specified for certain applications. For instance, France, Italy, the Netherlands and Spain have specified a minimum class of B2, d1, a1 for high-risk buildings like hospitals and multi-storey structures with large numbers of occupants.
Safer cable technology
LSZH cable jacketing may be made from thermoset or thermoplastic materials. Along with PVC, the halogenated cable jacket materials to avoid include CPE (chlorinated polyethylene), CSPE (chlorosulphonated polyethylene) and FEP (fluorinated ethylene propene). Non-halogenated alternatives include PE (polyethylene), PU (polyurethane), XLP (cross-linked polyethylene) and EPR (ethylene propylene rubber) (Figure 3).
Click image to enlarge
Figure 3: Belden is another key manufacturer, with LSZH products like the RG58C/U coaxial cable.
It should be noted that halogenated flame retardants are sometimes added to materials like XLP and EPR which would otherwise be halogen-free. Making cables flame-retardant without using halogens has been a major challenge. Additives such as aluminium trihydrate (ATH) or magnesium hydroxide (MDH) can achieve this.
To meet high flammability standards, large amounts of additive may be needed and the cable’s physical properties – such as flexibility – may be adversely affected. Processing may also be more complicated. However, cable manufacturers have found a variety of material combinations and processing methods to overcome the difficulties. Almost inevitably, these developments add to the cable price (figure 4).
Click image to enlarge
Figure 4: EcoWire hook-up wires are part of the EcoGen wire and cable family from Alpha Wire.
Choose with care
Although the CPR classification makes comparison and selection of safe cables easier, there are still thousands of cable products to choose from – and no two are the same. A few good examples are shown here to illustrate the variety. The advice of a cable specialist is invaluable in identifying the right cable for your application.