In enclosed public areas—such as hotels, hospitals, high-rise buildings, subway systems, and airports—plastic compounds used in wire and cable jacketing and insulation must be formulated with flame retardants that slow the spread of fire and produce low levels of smoke, so that people can be evacuated safely and quickly.
Some are concerned that conventional wire and cable compounds, which use PVC or halogen-containing flame retardants, may produce harmful fumes in a fire. A solution to this concern are low smoke halogen free (LSHF) compounds, which are flame retardant compounds that generate low amounts of smoke and contain no halogenated materials.
These compounds use a non-PVC plastic, and they use halogen-free flame retardants instead of halogen-containing ones. These compounds (and the flame retardants that go into them) are also known as “low smoke zero halogen” (LSZH or LS0H or sometimes LSOH) or as “halogen free flame retardant-low smoke” (HFFR-LS).
LSHF compounds are used in all kinds of industrial, energy, power, and data cable designs, including coaxial cables and fiber optic cables. LSHF compounds can also be used in areas containing expensive or sensitive equipment, including communication exchanges, offshore platforms, military applications, power generation facilities, oil and petrochemical installations and many others, because they produce less acid gas than halogenated compounds during combustion.
Halogen-free compounds are used in both Europe and the United States, although they may not offer enough flame retardancy to meet fire protection codes for certain applications.
What are halogens?
Halogens are a group of elements that include fluorine, chlorine, bromine, and iodine. These elements have many important uses. Any material that contains a halogen is called “halogenated.” If a material does not contain any of these halogens, it can be called “halogen free” or “zero halogen.”
Types of plastic used in wire and cable
PVC (polyvinyl chloride) and chlorinated polyethylene (CPE) are used in wire and cable. These are halogenated polymers because they contain chlorine. Many other types of non-halogenated plastics are also used. These include cross-linked polyethylene (XLPE), thermoplastics elastomers (TPE), thermoplastic olefins (TPO), thermoplastic polyurethane (TPU), and thermoplastic vulcanates (TPV).
Each of these polymers is tough and flexible, but other properties that are important to wire and cable, such as the temperature at which it can be used, its resistance to hydrolysis (i.e., material degradation caused by water), or its electrical properties (for example, how fast it transmits data) can vary.
A material expert can help users select the best material for a specific application. Flame retardants can be added to these materials. A HFFR compound is a non-halogenated plastic combined with a non-halogenated flame retardant.
Types of flame retardants
Bromine and chlorine are used to make halogenated flame retardants. Some types of brominated and chlorinated flame retardants have been phased out of use because of environmental and human health and safety concerns. While other types of brominated flame retardants are considered safe to use, some prefer to use halogen-free.
There are also many types of halogen-free flame retardants that do not contain bromine or chlorine. These HFFRs may be made with phosphorous, nitrogen, or inorganic minerals, such as magnesium hydroxide. Formulating a compound with HFFRs requires expertise to choose what combination of additives will produce the desired flame retardancy as well as performance properties, such as high strength, flexibility, and resistance to heat, moisture, and aging.
Experts at Mexichem Specialty Compounds have developed MEGOLON® LSHF compounds, for example, which have similar performance characteristics to PVC jacketing compounds, yet are non-halogenated. “MEGOLONâ LSHF compounds produce less smoke and less acid gas in a fire, compared to PVC and halogenated olefin systems. The excellent thermomechanical properties of MEGOLONâ compounds make them suitable for use in the manufacture of both power and telecommunication cables,” says Daniel DeLisle, General Manager.
Circuit integrity cables
Keeping people safe during a fire is the top priority, and this can include protecting cables that are vital for keeping power on so that fire alarms can sound, lights can work, and people can get out of harm’s way. Circuit integrity cables are designed to remain intact for as long as possible.
The flame retardant material in these cables forms char, which is a layer of burned material on the surface of a cable that protects the underlying components of the cable to allow it to continue to function.
Mexichem Specialty Compounds developed MEGOLON® S662, a HFFR sheathing compound with low smoke and enhanced char for greater protection. This extra protection can also give cable designers more freedom to use less-expensive protective tapes in the cable while maintaining fire protection.