Fire and smoke safety
Fire and smoke safety
WILLIAM B. GARDNER, AT&T
Power and telecommunications electrical and fiber-optic cables are often cited as the source or route of flame propagation in commercial building fires. On a worldwide basis, these issues have led to the generation of diverse sets of cable fire and smoke prevention standards among countries. Consequently, many international fire prevention tests exist to measure the fire retardation properties of lightwave cables and materials. These tests check ignitability, burning rate, flame spread rate and smoke and corrosive gas evolution rates.
In designing lightwave cables, a basic fabrication tradeoff involves the use of halogenated compounds in insulation and sheath materials. Halogens serve as efficient flame retardants, but in a fire, they often produce corrosive toxic emissions in the form of halogen-based acid gases.
Technical Subcommittee 20C of the International Electrotechnical Commission has therefore issued flame spread and fire retardance tests 331 and 332. The IEC 332, Part 3C large-scale fire test is approximately equivalent to the U.S. Underwriters Laboratories 1581 test. All the U.S. tests are written by National Electrical Code committees, and the tests are conducted and approved by the Underwriters Laboratories in accordance with National Electrical Code Article 800, issued by the National Fire Protection Association.
The European fire test IEC 332-1 describes a Bunsen burner test, for residential use only, which is equivalent to the Underwriters Laboratories VW-1 test. The large- and small-scale European tests are Harmonized Documents 405.3 and 405.1, respectively, and are issued by the European Committee for Electrotechnical Standardization, known as Cenelec. These documents consolidate IEC and European government tests. Although there is no equivalent European cable marking, every communications cable sold in the United States must be marked with a fire resistance measurement level.
The principal smoke-emission building-code standards are contained in the National Electrical Code Article 800; the comparative standards in Europe are found in IEC 1034 and in Cenelec HD 606.S1. The IEC 1034 standard, written by Technical Committee 89, implements the "3-meter-cube" smoke test, named for the volume of the test chamber used.
The U.S. Underwriters Laboratories 1685 test measures the peak smoke release rate and smoke emission; the UL 910 test measures the optical density of the produced smoke. All plenum cables in the United States must pass the UL 910 test.
If all the materials used to make a cable meet the requirements of IEC 754, Part 2, for acidic gas emission, that cable can be classified as zero halogen. Some vendors, however, have designated cables as low-smoke zero halogen when only the sheath material passes the test. In the event of a fire, obviously, there is a high probability that the other cable materials besides the sheath will burn.
If the only cable installation concern is flame spread, then building designers should specify IEC 332, Part 3. If smoke emission is also an installation concern, then IEC 1034 requirements should be incorporated. Moreover, adding corrosion and toxicity requirements calls for the specification of IEC 754, Part 2, which deals with acidic gas emission.
The International Electrotechnical Commission is not the only international standards organization that addresses fire and smoke safety. The International Telecommunication Union`s Study Group 6, Working Party 1, under the leadership of D.J. Dekker of the Royal PTT in The Netherlands, has approved a draft recommendation. This document, drafted by R. Salgado at Telefonica de Argentina, covers fire prevention, detection, extinction and codes for telecommunications facilities. q