Understanding the thermal degradation of an electric fire-resistant cable

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Understanding the thermal degradation of an electric fire-resistant cable Catherine Henrist*, André Rulmont*, Rudi Cloots*, Guenter Beyer+ * Department of Inorganic and Structural Chemistry Sart-Tilman B6, 4000 Liège University of Liège (Belgium) + Kabelwerk Eupen Malmedyerstrasse,9 B-4700 Eupen (Belgium) ABSTRACT The processing of fire-resistant non-halogeneted electric cables is a specific challenge. Metal hydroxides have always been extensively used as fillers in the insulating polymer sheaths. Recently, an hydrated zinc borate has been said to act in synergy with the traditionnal aluminium trihydroxide. We report the results of a microstructural investigation of a cable containing zinc borate in combination with aluminium trihydroxide, submitted to different heat treatments in order to get information about the structural modifications and the degradation of the electrical properties. We conclude with a short proposal to improve its efficiency. INTRODUCTION Fire constitutes a much larger problem than is generally perceived. Losses from all natural disasters combined – floods, hurricanes, tornadoes, earthquakes, etc…- average a fraction of the annual direct dollar losses from fire. Deaths from disasters have tended to be vastly fewer than from fires – on the order of 200 per year in disasters versus nearly 5,000 in fires, for the United States[1]. In the United States, there are millions of fires, thousands of deaths, tens of thousands of injuries and billions of dollars lost. Although much progress have been made in the last two decades, the US continues to have one of the highest per capita fire death rates in the world. In terms of dollar loss, the estimated direct value of property destroyed in fires was $ 9.4 billion for 1996. These casualties and losses come from an average of nearly 2.1 million fires annually. Most fires are relatively small, and their cumulative impact is not easily recognized. Very few of them generate huge losses, but because most of the losses from fire are spread over 2 million fires that are reported each year, the total loss is far more than the impression many people have from the anecdotal reporting of local fires in the media. Fires also are an important cause of accidental deaths. The National Safety Council ranks fires as the fifth leading cause of accidental deaths behind only : vehicle accidents, falls, poisoning and drowning. Classes of fires Fires can belong to several types depending on their combustible[5]. Class A-fires are called "dry fires" because they concern solid materials made of organics such as wood, cotton, paper, plastics… The combustion of these materials can be of two sorts: either flaming or slow combustion without flaming but with glowing embers. Class B-fires are also called "oily fires": grease, paint, varnish, tar, alcohol, solvents, …The vapors emitted by boiling of the liquid, when

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mixed with atmospheric oxygen, are responsible for the combustion. Finally, class C-fires-or "gas-fires" concern gases such as butane, propane, methane, acetylene

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