Flame Retardant Cables Research Articles

Обоснование безопасного расстояния между размещенными в одной пожарной зоне кабелями каналов безопасности атомных электростанций с водо-водяными реакторами

Currently, there are no methods of mathematical modeling of the operability of power and signal cables used at the nuclear power plants in real and standard fire conditions, including the use of intumescent flame retardants. The purpose of the article is a theoretical assessment of the safe distance between the cables of the safety channels of nuclear power plants with pressurized water reactors located in the same fire zone. To achieve it, the time of occurrence of a short circuit in the cables of the channels of safety systems from the beginning of a real fire and depending on the distance between adjacent cable lines was estimated. An integral method of mathematical modeling of the development of a fire in a room is used. To determine the temperature distribution inside the cable insulation, the thermal conductivity equation is solved. The analysis of the obtained results is carried out. The calculation results made it possible to formulate the requirements for the swelling temperature of fire retardant compounds for treating the outer surfaces of SB cables: the above temperature should be no more than 150 °C for the flame retardant cables, and 180 °C for the non-flame retardant cables, as well as at distances between open cables of two safety systems smaller than 2, the outer surfaces of the safety cables must be treated with a fire retardant compound with a fire retardant efficiency of at least 120 minutes. The conducted theoretical assessment of the safe distance between the cables of the safety channels of nuclear power plants with pressurized water reactors located in the same fire zone, using the proposed mathematical model, showed that in a real fire, in order to prevent a short circuit in the cables of the safety systems, as well as ignition of the insulation of adjacent cables, it is required to justify safe distances between the adjacent cables of the safety system of nuclear power plants, taking into account the specific dimensions of the premises and the properties of the cable insulation material and the fire-retardant coatings used.

Application of Magnesium Hydroxide/Diphenoxy Phosphate in Silicone Rubber Flame Retardant Cable Material

Deketoxime–type room–temperature vulcanized silicone rubber cable materials were prepared using α, ω–dihydroxy polydimethylsiloxane, carbon black, calcium carbonate, magnesium hydroxide, piperazine bis (diphenoxy phosphate) salt (PBDP), and melamine diphenoxy phosphate (MDP). The effects of carbon black and flame retardants on the mechanical properties, flame–retardant properties, and electrical insulation properties of silicone cable coatings were investigated. The research results showed that the products obtained had good mechanical and electrical insulation properties, with tensile strength greater than 3.0 MPa, dielectric strength greater than 22 kV/mm, and volume resistivity higher than 6.5 × 1014 Ω·cm. When 30 parts of Mg(OH)2:MDP = 2:1 are added to 100 parts of resin, the flame–retardant performance of wire and cable materials can be significantly improved. Under the thermal radiation illumination of 50 kW/m2, the ignition time (TTI) of the Mg(OH)2/MDP coating increased by 16 s, and the maximum heat release rate (pkHRR) and total heat release rate (THR) decreased by 29.7% and 68.8%, respectively, compared with silicone rubber without flame retardant. The silicone rubber coatings prepared were flame retardant up to the FV–1 level.

Combustion characteristics and thermal decomposition mechanism of the flame-retardant cable in urban utility tunnel

Although urban utility tunnel act as innovative technique for sustainable development, the cable fire of tunnel should be carefully treated. Extensive studies have usually focused on the combustion or pyrolysis stage of cables by a single test, but comprehensive tests still need to further investigation. Therefore, the cable ignition, expansion charring, pyrolysis and combustion from the macro and micro perspectives were comprehensively explored with cone calorimeter and simultaneous thermal analysis infrared gas chromatography (STA-FTIR-GC/MS). It was found that in addition to the outermost sheath material of the cable, its insulation material and flame retardant material play a non-negligible role in the fire. To more accurately reflect the actual pyrolysis and combustion characteristics of the material, a simplified cable ignition model was established, the combustion laws of typical cables in the urban utility tunnel under different radiation intensities were explored, the quantitative characterization and risk assessment of the toxicity of the gas products were studied.What's more, the pyrolysis characteristics and reaction mechanism of cables under different thermal environments were revealed. The work provides the necessary support for the establishment of database and design standard of fire engineering in urban utility tunnel.

On the pyrolysis characteristic parameters of four flame-retardant classes of PVC sheathless cable insulation materials

Flame retardant cables are widely used today, while the comparison of thermal degradation behavior between PVC cable insulation materials with different flame-retardant levels has not been extensively studied so far. The thermal degradation behaviors of four flame-retardant and one non-flame-retardant PVC cable insulation materials were studied using thermogravimetric (TG) analysis and a combination of TG-Fourier transform infrared analysis. Generally, TG data differ at the first peaks but are similar at the second peaks for various types of insulation materials. This is because the reaction mechanisms of the first pyrolysis stage vary with the change of flame-retardant level, while the second pyrolysis stage is similar regardless of the flame-retardant level. Besides, the flame-retardant performance level cannot solely be evaluated based on the activation energy of these insulation materials. The coupled Fourier transform infrared spectroscopy (FTIR) shows that during the pyrolysis of flame-retardant PVC insulation materials (ZA-BV, ZB-BV, ZC-BV, and ZR-BV), the amount of the seven major released components, arranged in order from most to least, is C-H bending > H2O > C-H stretching > CO2 > C-H aliphatic bending > CH2 deformation > C-Cl stretching. While for the non-flame-retardant PVC insulation material (BV), the series is CO2 > C-H bending > C-H stretching> H2O > C-H aliphatic bending > CH2 deformation > C-Cl stretching. The reported results provide a basis to evaluate the thermal degradation behavior of typical PVC cable insulation materials at present and can also provide essential data for the numerical simulation of an electrical fire.

Effects of Quantity and Arrangement of a Flame-Retardant Cable on Burning Characteristics in Open and Compartment Environments

The results of cable burning experiments conducted in a well-controlled or open environment may differ from fire phenomena in an actual installation environment of cables where the effects of ventilation conditions and thermal feedback exist. In order to prevent the misunderstanding of fire phenomena due to these differences, the changes in burning characteristics in open and compartment environments were investigated for a flame-retardant (TFR-8) cable and general PVC (VCTF) cable arranged on three-layer trays. As a result, it was confirmed that the fire scale, fire spread area, and cable damage varied greatly depending on the cable arrangement under the same cable quantity condition. Furthermore, the maximum heat release rate (HRR) and fire growth rate of TFR-8 in the compartment environment increased more than 3-times compared to the open environment, and showed a similar level of fire risk to VCTF even though it is a flame-retardant cable. Additional experiments using vertical and horizontal openings of various shapes were conducted to evaluate the individual contributions of thermal feedbacks from the wall and smoke layer to the changes in burning characteristics within the compartment. The results of this study can be used as basic data to reduce fire damage while providing an essential understanding of cable fire phenomena.

Measurement of Pyrolysis Properties for Fire Spread Simulation of Cables

The analysis and review of the thermal decomposition properties required for the fire spread simulation of cables composed of multiple materials were performed. Thus, a typical two-step pyrolysis reaction was identified independent of cable type. It is expected that the Kissinger and flynn–wall–ozawa (FWO) methods, which are calculated using various heating rates, more accurately predict fire spread than the input method that uses the and values calculated using a single heating rate. Consequently, in the case of flame-retardant cables (CLASS 1E and TFR-8), the Kissinger method is more likely to overestimate the fire spread rate than the FWO method. In the case of polyvinyl chloride (PVC) cables (vinyl cabtire power cable, VCTF), the fire spread rate may be underestimated.

Rheological and Aesthetical Properties of Polyolefin Composites for Flame Retardant Cables with High Loading of Mineral Fillers

It was found that the use of natural magnesium hydroxide (n–MDH) as mineral filler in EVA based composites provided mechanical and rheological properties that did not completely comply with the halogen-free flame-retardant (HFFR) cables parameters. Moreover, the use of n–MDH mostly gave a rough grey surface in the compound extruded by rheometry capillary. In contrast, with the use of synthetic material (s–MDH), a combination of better outcomes was observed. Mechanical and rheological properties were more aligned with the application, and the aesthetics were also improved, i.e., the surface was smooth and whiter. Therefore, with the aim of obtaining good aesthetical quality on the extrudate, we studied formulations by varying the type of polymer matrix and using a mixture of the natural magnesium hydroxide combined with other kind of fillers (in a 3:1 ratio using as main filler n–MDH). On this account, we found a synergistic effect in the mechanical, rheological, and aesthetic properties for the filler blend system containing n–MDH in combination with s–MDH or Böhmite AlO(OH), or using a secondary polymer belonging to the polybutene family combined with EVA.

Experimental investigation on the impact of cable fire products from flame-retardant cables on catalysts used in passive auto-catalytic recombiners

Cable fires in nuclear power plants have a significant probability to occur at any time in the course of a severe accident or may as well be the initiating event of a severe accident sequence. During the combustion process, enormous amounts of aerosols alongside specific combustion gases (e.g. CO, CO2) can be released. Both nature and amount of the cable fire products depend on the combustion conditions. The effect of cable fire products distributing inside the containment and getting in contact with the catalyst surfaces of passive auto-catalytic recombiners (PARs) is of vital interest for safety analyses, in order to assess the hydrogen mitigation efficiency under these conditions.The newly built REKO-Fire facility at Forschungszentrum Jülich combines a flow tube reactor for catalyst investigation with a steady-state tube furnace for the constant generation of cable fire products at varying combustion conditions. That way, simultaneous exposure of 5 × 5 cm2 catalyst samples to cable fire products and hydrogen/air mixtures is possible, enabling to quantify the influence of gaseous and particulate components on the catalysts’ start-up behavior. The installation has been used in the present study to investigate the effect of cable fire products obtained from flame-retardant power cables under three different fire conditions on the start-up of two types of catalysts for hydrogen recombination.For well-ventilated cable fire, neither gaseous nor particulate (mainly soot) cable fire products seem to affect the onset of the catalytic H2 conversion for both Pt and Pd-based catalysts. In under-ventilated fire conditions, the Pt-based catalyst is significantly deactivated, while the only impairment for the Pd-based catalyst is observed at very low hydrogen concentrations. For cable fire products generated from oxidative pyrolysis, the overall picture is ambiguous. On the one side it is obvious that deactivation and start-up delay occur for both catalyst types. However, no clear conclusion can be taken from the experimental data concerning the effect of exposure time. The presence of carbon monoxide in the atmosphere as well as particulate depositions from cable pyrolysis seem to be the most relevant mechanisms for catalyst deactivation and deserve further investigation.

A Method for Determining the Impact of Ambient Temperature on an Electrical Cable during a Fire

Evaluating environmental conditions that trigger fire-fighting equipment is one of the primary design tasks that have to be taken into account when engineering electrical systems supplying such devices. All of the solutions are aimed at, among others, preserving environmental parameters in a building being on fire for an assumed time and at a level enabling safe evacuation. These parameters include temperature, thermal radiation, visibility range, oxygen concentration, and environmental toxicity. This article presents a new mathematical model for heat exchange between the environment and an electric cable under thermal conditions exceeding permissible values for commonly used non-flammable installation cables. The method of analogy between thermal and electrical systems was adopted for modelling heat flow. Determining how the thermal conductivity of the cable and the thermal capacity of a conductor-insulation system can be applied to calculate the wire temperature depending on the heating time t and distance x from the heat source is discussed. Thermal conductivity and capacity were determined based on experimental tests for halogen-free flame-retardant (HFFR) cables with wire cross-sections of 2.5, 4.0, and 6.0 mm2. The conducted experimental tests enable verifying the results calculated by the mathematical model.

Optimization of the Mechanical Properties of Polyolefin Composites Loaded with Mineral Fillers for Flame Retardant Cables

Formulations based on mineral fillers and polymeric matrices of different nature were studied to obtain halogen-free flame retardant compounds (HFFR) for cable applications. The work was carried out by comparing fire-retardant mineral fillers of natural origin with synthetic mineral ones available on the market. As a reference, a formulation based on micronized natural magnesium hydroxide (n-MDH, obtained from brucite) and an ethylene-vinyl acetate copolymer with 28% by weight (11% by moles) of vinyl acetate were selected, and the mechanical and flame retardant properties compared with formulations based on secondary polymers combined with EVA, metal hydroxides, and carbonates. Notably, we found a synergistic effect in the mechanical, rheological and flame retardant properties for the composite containing a mixture of n-MDH and boehmite in a 3:1 weight ratio. Overall, the present work provided a complete and optimized recipe for the formulation of polymer composites characterized by the required flame retardant and mechanical features in electric cables applications.

A comprehensive study on the flame propagation of the horizontal laboratory wires and flame-retardant cables at different thermal circumstances

Experiments were performed to carefully characterize the influence of ambient temperature and incident heat flux on the horizontal flame spread over wires and cables. Results show that the flame spreads evenly along the wire, and the flame spread rate slightly increases with the ambient temperature increasing with a maximum increase of 16 %. However, the change of the flame front position with time for the cable presents a piecewise linear function, and an accelerating process exists. As the incident heat flux increases, the flame spread rate increases significantly with a maximum increase of 110 % and 113 % for both single and double cable. There is no spreading flame over the cable below a lower limit of the incident heat flux. The fastest flame spread along the cable occurs when the incident heat flux causes the flame to extend to the end of the fuel instantly. Compared to the single cable, the flame spread rate of double cable is increased by 13.6%–16.2% due to the enhanced heat feedback by the flame interaction effect. The difference in flame spread behavior in this work may be ascribed to different physical configurations, chemical compositions, reaction mechanisms, and heat transfer mechanisms.

Experimental and Numerical Studies on Major Pyrolysis Properties of Flame Retardant PVC Cables Composed of Multiple Materials.

Flame retardant cables were investigated using thermo-gravimetric analysis to measure the reference temperature and reference rate required for a fire spread simulation using a Fire Dynamics Simulator (FDS). Sensitivity analysis was also performed to understand the effects of the reference temperature and rate on the pyrolysis reactions. A two-step pyrolysis reaction was typically observed regardless of the cable type, and each pyrolysis reaction could be attributed to single or multiple components depending on the cable type and reaction order. Although the structures, compositions, and insulation performances of the cables differed considerably, the reference temperatures of the two-step pyrolysis reaction were extremely similar regardless of the cable type. Conversely, the reference rates of the different types of cables varied significantly. The sensitivity analysis results indicate that the mean values of the reference temperature and rate are sufficient to simulate the pyrolysis reactions of flame retardant cables. The results obtained herein also suggest that the heat transfer and pyrolysis reaction path associated with the multi-layered cable structure may be more important for accurately determining the ignition and fire spread characteristics, which are attributable to differences in cable structure, composition, and insulation performance.

Study on Flame Spread Characteristics of Flame-Retardant Cables in Mine

Polymer combustion is an important factor in mine fires. Based on the actual environment in a mine tunnel, a cable combustion experiment platform was established to study the regularities of the cable fire spread speed and smoke temperature under different conditions, including various fire loads and ventilation speeds. The flame change and molten dripping behaviour during the fire spread process were also analyzed. The experimental results show that the flame-retardant cable can be ignited and continuously burnt at a certain wind speed, but the combustion can be restrained at high wind speed. The combustion speed of the flame-retardant cable is affected by the fire load and ventilation speed. The combustion droplets can change the shape of the flame, which can consequently ignite other combustible materials. The analysis of the experimental results provides an important basis for the prevention of tunnel fires.

Study of gases released under incomplete combustion using PCFC–FTIR

In order to get new insights on cable behavior during real-scale fires, the gases released under incomplete combustion in pyrolysis combustion flow calorimeter were recorded for several PVC and halogen-free flame-retardant cables. Incomplete combustion was monitored by changing combustion temperature between 600 and 900 °C. Gases were identified using PCFC–FTIR coupling. Quantitative assessment of different gases produced during combustion was also carried out. It appears that larger amounts of unburnt gases are produced for PVC cable at low temperature (< 650 °C). Moreover, CO release is observed for PVC cable up to 800 °C while this gas disappears between 700 and 750 °C for halogen-free flame-retardant cables. Interestingly, the CO production is non-monotonous upon the temperature range investigated. These analyses would be useful to assess the risk of multiple re-ignitions during cable burning in real-scale fires, especially in confined compartments.

Effects of Insulating Material Ageing on Ignition Time and Heat Release Rate of the Flame Retardant Cables

Abstract The effects of insulating material ageing on the fire performance of flame retardant cables were investigated experimentally by cone calorimeter in the present study. The ageing time and ageing type of the insulating material were concerned, and the fire hazard of cables was represented by the ignition time and the heat release rate (HRR). The results show that both the ignition time and the peak of HRR increase with the ageing time first and then decrease slightly for the flame retardant control cables with polyvinyl chloride insulated and polyvinyl chloride sheathed (ZR-KVV). For the flame retardant control cables with crosslinked polyethylene insulated and polyvinyl chloride sheathed (ZR-KYJV), the ignition time increase and the peak of HRR decrease with the ageing time. The effects of ageing type of insulting material on fire hazard of cables were investigated with the ZR-KVV cables. The ignition time and the HRR of the thermal aged cables were higher than those of the xenon arc aged cables, the ozone aged cables and the hydrothermal aged cables. The results of fire hazard assessment of aged flame retardant cables according to the ignition time might be opposite to those derived from the HRR of cable fires, which should be paid attentions in cable fire safety evaluations.

Fire behaviors of flame-retardant cables part I: Decomposition, swelling and spontaneous ignition

Electrical cable is a potential ignition source and fire hazard in residential houses, nuclear power plants, aircraft, and spacecraft. In this work, a bench-scale flame-retardant cable, consisted of the outer PVC sheath, middle XLPE insulation, and inner copper core, was heated uniformly inside a novel cylindrical heating chamber. The applied heat flux was transient, which increased with time close to a parabolic function. Once heated, the outer PVC sheath swelled and shrank under multiple stages. Before ignition, the swelling behavior was found to follow the same trend as the mass-loss rate. Analysis showed that the observed spontaneous ignition was likely a result of pyrolysis gas from inner XLPE insulation piloted by the smoldering hot spot (600~700 °C) on the outer charring PVC sheath. For the first time, the spontaneous ignition time was found to linearly increase with the integral heat flux, and it was different from other ignition experiments under the transient heat flux in the literature. Moreover, the measured critical mass flux of ignition increased with the heating power, and the critical surface temperature of PVC was above 500 °C. The results of this work provide important information about the swelling and ignition behaviors of the flame-retardant cable under a real fire, and may guide the design of future fire-safety cable.

Fire behavior of halogen-free flame retardant electrical cables with the cone calorimeter

Fires involving electrical cables are one of the main hazards in Nuclear Power Plants (NPPs). Cables are complex assemblies including several polymeric parts (insulation, bedding, sheath) constituting fuel sources. This study provides an in-depth characterization of the fire behavior of two halogen-free flame retardant cables used in NPPs using the cone calorimeter. The influence of two key parameters, namely the external heat flux and the spacing between cables, on the cable fire characteristics is especially investigated. The prominent role of the outer sheath material on the ignition and the burning at early times was highlighted. A parameter of utmost importance called transition heat flux, was identified and depends on the composition and the structure of the cable. Below this heat flux, the decomposition is limited and concerns only the sheath. Above it, fire hazard is greatly enhanced because most often non-flame retarded insulation part contributes to heat release. The influence of spacing appears complex, and depends on the considered fire property.

Effects of External Heat Radiation on Combustion and Toxic Gas Release of Flame Retardant Cables

The effects of external heat radiation on combustion and toxic gas release characteristics of flame retardant cables, which were XLPE insulated, flame retardant PVC sheathed and steel armoured cables, were investigated. The combustion characteristics of the level A and the level C flame retardant cables were explored by the cone calorimeter. For the level C cables, heat release rate (HRR) and CO concentration in cable fires increased and the ignition time decreased with increase of the external radiation heat flux. For level A cables, the HRR and CO concentration showed two-stage variations with the external radiation heat flux. When the external radiation heat flux was smaller than 35 kW/m2, the cable self-extinguished quickly after the ignition. When the external radiation heat flux was larger than 50 kW/m2, the cables showed continuous burning phenomena after the ignition. The level A cable had smaller HRRs compared with that of the level C cable under the same external radiation heat flux. However, the CO concentration of level A cable was remarkably higher than that of the level C cable in the present study. The high CO release rate of cable with well flame retardant ability under large external radiation heat flux requires more caution in the cable fires.

경년열화 전선케이블의 탄소산화물 및 발연특성변화 감식

본 연구에서는 공동지하구의 밀폐된 환경에서 사용되고 있는 전력용 케이블(CV-Cable)의 연소패턴을 예측하기 위하여 경년열화(29년, 14년, 10년 사용)된 케이블의 외피를 준비하여 열적특성 및 난연특성을 비교 분석하였다. 발연특성 및 난연특성 분석을 위한 실험은 ISO 5659(연기밀도), UL 94(난연성), NES 713(독성가스) 등의 규격에 의하였다. 연구결과, 총연기방출량은 29년 경년은 <TEX>$3554(m^2/m^2)$</TEX>, 14년 경년은 <TEX>$2735(m^2/m^2)$</TEX>, 10년 경년은 <TEX>$2342(m^2/m^2)$</TEX>로 나타나 사용연수가 길수록 총연기방출량은 증가하는 경향을 보였다. 또한, 최대연기밀도는 경년별 924Dm으로 동일하였으나 난연케이블의 연기밀도 성능 기준인 150Dm 이하 보다 6.16배 높은 것으로 나타났다. 독성지수는 29년 경년의 경우 2.7, 14년 경년은 1.7, 10년 경년은 0.6으로 나타나 29년 경년 케이블은 10년 경년 케이블 보다 독성지수가 4배 이상의 높은 것을 알 수 있었다. In this study, outer cover of temperature aging(used for 29 years, 14 years, 10 years) cables were prepared for comparative thermal characteristics and retardant characteristics to predict combustive pattern of power cables(CV-Cable) that are being used in sealed environment of common utility tunnel. ISO 5659(smoke density), UL 94(flame retardancy), and NES 713(toxic gas) standards were followed for tests for analysis of smoke generation characteristics and flame retardant characteristics. As result of research, total smoke release of 29 passed years, 14 passed years, and 10 passed years were shown a <TEX>$3554(m^2/m^2)$</TEX>, <TEX>$2735(m^2/m^2)$</TEX>, and <TEX>$2342(m^2/m^2)$</TEX>, respectively in which tendency of increasing total smoke release was shown as used years increased. Also, maximum smoke density was identical to 924Dm by passed years and was shown to be 6.16 times higher than the smoke density performance standard of flame retardant cables which is 150Dm or lower. Toxic index was shown to be 2.7, 1.7, and 0.6 for 29 passed years, 14 passed years, and 10 passed years, respectively in which 29 passed year cable showed more than 4 times higher toxic index that 10 passed year cable.

트레이용 난연 전력 케이블의 화재특성에 관한 실험적 연구

The present study has been conducted to investigate the fire combustion properties and fire behavior of an IEEE-383 qualified flame retardant cable. The reference reaction rate and reference temperature which are commonly used in pyrolysis model of fire propagation process was obtained by the thermo-gravimetric analysis of the cable component materials. The mass fraction of FR-PVC sheath abruptly decreased near temperature range of <TEX>$250{\sim}260^{\circ}C$</TEX> and its maximum reaction rate was about <TEX>$2.58{\times}10^{-3}$</TEX>[1/s]. For the XLPE insulation of the cable, the temperature causing maximum mass fraction change was ranged about <TEX>$380{\sim}390^{\circ}C$</TEX> and it has reached to the maximum reaction rate of <TEX>$5.10{\times}10^{-3}$</TEX>[1/s]. The flame retardant cable was burned by a pilot flame meker buner and the burning behavior of the cable was observed during the fire test. Heat release rate of the flame retardant cable was measured by a laboratory scale oxygen consumption calorimeter and the mass loss rate of the cable was calculated by the measured cable mass during the burning test. The representative value of the effective heat of combustion was evaluated by the total released energy integrated by the measured heat release rate and burned mass. This study can contribute to study the electric cable fire and provide the pyrolysis properties for the computational modeling.