Flame retardancy in halogen-free cables

Halogens (meaning “salt formers”) include the chemical elements chlorine (Cl), bromine (Br), fluorine (F), and iodine (I). In cable manufacturing, these elements are used to make certain insulation and sheathing materials flame-retardant. Chlorine (which is a component of PVC plastic or chloroprene rubber) and fluorine (found in the high-temperature materials FEP, PTFE, and ETFE) play a role here. Even bromine is used in flame retardants for cables and wires.

The problem is that halogens burn very aggressively and emit toxic fumes when ignited. They produce halides which, when in contact with moisture, turn into acids that can cause acid burns in the respiratory tract. In addition, the released acids can corrode metal parts, which can damage machinery and even the reinforcement of concrete in buildings. This can result in time-consuming and expensive remediation measures.

The flame retardancy of cables and wires is of course an important criterion for fire prevention measures. There are also a number of applications that explicitly require halogen-free products, which means that cables and wires consist of materials that are free of chlorine, bromine, fluorine and iodine. If these cables catch fire, they produce much less acid and smoke, and are less toxic, which significantly reduces the consequential damage to people, buildings and machines. However, even halogen-free cables still emit toxic gases such as carbon monoxide when they catch fire.

For example, halogen-free cables and wires are required in buildings where people come together and where valuable material goods need to be protected. Examples include:

• Building technology: Public buildings such as offices, shopping malls, schools, hospitals and airports are subject to strict fire and health regulations. Most cables and wires in these buildings are permanently installed and do not have to meet any special chemical or mechanical requirements. PE or PP-based plastic compounds are often used here, which are halogen-free, flame-retardant and produce little smoke or toxic gas. They also often have to pass bundle combustion tests.
• Industrial Automation: Machines and installations often require cables and wires with high chemical and mechanical resistances. When used in flexible applications such as in drag chains or in robotics, these loads are particularly high. Typically, sheathing materials based on TPE-O or TPE-U (PUR or Santoprene) are used here. These are also available in halogen-free versions, but cannot be produced as flame-retardant or low-smoke as cables for building technology.

Over the years, different manufacturers, markets, regions and standards have developed different labels for halogen-free and flame-retardant cables:

• FRNC: Flame Rtarnished Non Ccorrosive
• HFFR: Halgae Fdeer Flame Rtarnished
• LS0H: Low Smoke 0Halgae (also: LSOH)
• LSZH: Low Smoke Zthere Halgae

However, none of these labels provide specific information on flame retardancy, corrosiveness, toxicity and light attenuation. Users should therefore pay close attention to the standards stated in the data sheets of each supplier. The information stated there is the only way to identify the flammability properties of a cable (horizontal, vertical or bundle burning tests).

DIN EN 60754-1 VDE 0482-754-1:2021-02 defines the test machines and test procedures needed to identify total acidity. The test result must show values below 5 mg/g to be certified as halogen free.

DIN EN 60754-2 VDE 0482-754-2:2021-02 defines the measurement of pH and conductivity. The pH must be less than 4.3 and the conductivity must be less than 10 µS/mm to be certified as halogen-free.

DIN EN 61034-2 VDE 0482-1034-2:2021-02 defines the measurement of the smoke gas density of burning cables. The test result must show a light attenuation of maximum 40% to be considered low-smoke. Depending on the application, customer and region, stricter requirements for light attenuation may be imposed. The aim is that people can still recognize the fire source and possible escape routes. These standards are required in public buildings and trains due to the high density of people present.

In many safety-critical applications, halogen-free cables and wires offer significant advantages by reducing the release of toxic gas and smoke in the event of a fire. At the same time, these products must exhibit high flame retardancy to meet various standards and requirements. It is not enough to rely on common labels such as FRNC, HFFR, LS0H or LSZH to determine the actual flame retardancy of a cable. The standards listed in the data sheets are the only information you can rely on. It is through these standards that users can determine whether the product is considered low, medium or high flame retardant, whether it is designed to be low-smoke, or whether it has been tested for light attenuation. As experts in electrical connection technology with over 45 years of experience, HELUKABEL is happy to help you identify the most suitable cables and wires for your application.