By Robert Bellassai, Underwriters Laboratories
There is a lot of confusion in the industry regarding claims, mostly self-certified, of low-smoke halogen-free cables and the materials used in these cables.
Product claims about low-smoke halogen-free (LSHF)-also known by the industry as low-smoke zero-halogen (LSZH)-have been with us for some time now. Of note, these claims are frequently self-certified and tests used may not be standards-based. More importantly, there are some misconceptions about what some tests actually cover, which this article aims to clear up.
LSHF products originated in Europe and the U.S. in the 1970s. In the 1980s they were used in applications such as the London Underground, U.K. Navy and North Sea offshore oil drilling platforms. LSHF cables were installed in confined spaces where the toxicity and corrosivity of the smoke generated in a fire would be particularly problematic. The adoption of LSHF cable products has been slow in the U.S., but that has changed due to some high-profile fires. A key example is the January 12, 2015 L’Enfant Plaza incident in Washington D.C., during which a fire caused by an electrical malfunction filled a tunnel with smoke, killing one person and injuring others.
LSHF cable products have traditionally been found in the power and control categories, but now have branched out to categories including data/telecom cables, fiber-optic cables and appliance wire and cable. They also are being used in more locations than the traditional confined spaces (tunnels, subways, ships, submarines and mines), and are now also found in hospitals and data centers. UL will be proposing the optional HF and LSHF Marking for the 2020 edition of the National Electrical Code.
Asia and South America are also adopting LSFH wire and cable, which has been the EU approach to cable standards. In a global economy manufacturers now have access to a standards-based LSFH cable designation, and cable designers can produce one design that can be sold and applied around the world.
To better understand LSHF, we need to consider what a halogen is in terms of the Periodic Table of Elements. The five halogen elements found in Column 17 are fluorine, chlorine, bromine, astatine and iodine. The three primary elements found in insulation, filler and jacket materials/components are chlorine, bromine and fluorine.
Four predominant wire and cable industry standards-IEC 60754-1, IEC 60754-2, IEC 61249-2 Non-halogenated series, and MIL DTL-24643C Part 3.3 (NEMA WC57)-continue to be the source of some of the confusion regarding the halogen content of cable and materials. In particular, there is still an incorrect association, primarily with IEC 60754-1, “Test on Gases Evolved During Combustion of Materials from Cables-Part 1: Determination of the Halogen Acid Gas Content,” and IEC 60754-2, “Test on Gases Evolved During Combustion of Materials from Cables-Part 2: Determination of Acidity (by pH measurement) and Conductivity.”
These standards do not test for or reference chlorine, bromine or fluorine content levels; they are methods to test the halogen acid content-via titration method in the case of IEC 60754-1 and pH and conductivity for IEC 60754-2-established from the combustion of the tested material. Also, for IEC 60754-2, the minimum pH value of 4.3 and maximum conductivity of 10 μS/mm are described as “recommended performance requirements” as shown in Annex A of the standard. This recommendation implies that these requirements are “suggestive” as opposed to “normative” requirements.
The IEC recently developed the LSHF 62821-1, -2, and -3 standard series, “Electric Cables - Halogen-Free, Low-Smoke, Thermoplastic-Insulated and Sheathed Cables of Rated Voltage Up to and Including 450/750 V.” This series is one of the first to provide component material hydrogen free (HF), complete cable smoke requirements and applicable LSHF cable surface marking.
As a result of the publication of this standard, UL launched two new certification programs: a Material Recognition service and an optional Cable Surface Mark program.
The Material Recognition service uses test methods from IEC 60754-1/-2 and IEC 62821-1/-2 as described under Subject Outline UL 2885, “Outline of Investigation for Acid Gas, Acidity and Conductivity of Combusted Material and Assessment of Halogens,” dated 2015-02-12. This service is geared to support suppliers of insulation and jacket compounds, and cable components such as filler, tapes, wraps and the like. It can be summarized as follows.
IEC 60754-1. Under the UL 2885 standard, combustible materials are evaluated for the amount of Hydrogen Chloride (HCl) and then classified to a Performance Level Category (PLC). The PLC chart as shown in Table 8.1 of UL 2885 was developed by UL and is not found in IEC 60754-1. Combustible materials (insulation, jacket, fillers, tapes, etc.) evaluated under this service/standard(s) would not make claims or assertions to the halogen content of the material(s) and are not appropriate for use in validating cable products or their material components as non-halogen (ed.), zero halogen, halogen-free, low halogen or LSZH.
IEC 60754-2. Combustible materials for this standard under UL 2885 are evaluated for pH and conductivity. Combustible materials (insulation, jacket, fillers, tapes, etc.) evaluated under this service/standard(s) and are not appropriate for use in validating cable products or their material components as non-halogen (ed.), zero halogen, halogen-free, low halogen or LSZH.
IEC 62821-2/-2. Under the UL 2885 standard, combustible materials are evaluated for halogen content. Materials evaluated under this standard will allow for the “HF” Material Recognition designation for any combustible compound/component in a finished cable. Suppliers of insulation and jacket compounds and cable components may choose to obtain a Material Recognition for any one or more of the above standards.
For wire and cable manufacturers, UL established a “-HF” and “-LSHF” Cable Surface Mark designation in accordance to IEC 62821-3 (e.g. Type CMR-LSHF or OFNR-LSHF, TC-LSHF, RHHW-HF, CM-HF, SJO-HF, etc.). We announced this program in an Announcement Bulletin, “Halogen Free (HF) and Low Smoke Halogen Free (LSHF) Service Offerings for Wire and Cable,” dated 2015-02-20.
Under the “-HF” and “-LSHF” cable program, all combustible materials (insulation, jacket, fillers, tapes, wraps, shields, etc.) must first be recognized under UL’s Material Recognition Program as per UL 2885 (described above) or tested individually by the cable manufacturer. The cable manufacturer would be authorized to use these HF Recognized materials in order to apply the “-HF’ and “-LSHF” optional Cable Surface Mark.
Under the optional Cable Surface Mark program, no reference is permitted, within the UL print legend surface print, regarding non-halogen, non-halogenated, zero halogen, low halogen or LSZH or reference material provided by the cable manufacturer at these designations are not covered in the IEC 62821-3 standard.
Currently, UL has certified seven wire and cable companies to mark certain cable constructions as “HF” and “LSHF” and 10 suppliers of HF compound material to the wire and cable industry.
Legal fallout remains from fatal tunnel fire
The fatal fire at the Washington, D.C. Metro’s L’Enfant Plaza, which is referenced in this article and occurred on January 12, 2015, spurred a legal battle that is unresolved more than two years after it occurred.
On January 10, 2017, The Washington Post’s Martine Powers reported on the litigation. Dozens of passengers, as well as the family of the late Carol Glover who perished in the fire, filed a civil suit against Washington Metro. In response, Metro sought a dismissal of the case but also filed a counterclaim that cites a “chaotic and ineffective response,” on the part of emergency responders, Powers reported. -Ed.