WCA January 2016

❍ ❍ Table 1 : Fire performance parameters and their correlation to fire risk elements But this class of material is not the perfect solution, either. To achieve a very good fire performance one must use these ingredients in higher concentration. This reduces the mechanical performance of that cable, causes embrittlements or reduces the operating temperature range. If the probability is reduced down to 4 and the impact down to 5, a risk level of 20 as a product of the factors 4*5 is achieved. If the impact remains on its high level of 10, the probability must be reduced down to 2 to achieve the same risk level. Keeping in mind the Pareto principle, it will be clear that the effort to achieve this extremely low level of one factor will exceed the effort to keep both factors on a medium level. The advantage to distribute the efforts of risk reduction to both factors (avoidance and impact reduction) is shown in Figure 2 . The dashed line shows the risk depending on reduction efforts if all efforts are invested into threat avoidance. The continuous line shows the risk if the reduction efforts are distributed to both avoidance and impact reduction in the same quantity. Some simplifying assumptions are done in this approach to show the basic principle easily. It can be clearly seen that just in the medium part of the range, the distribution of efforts to both factors brings clear advantages. This paper does not dive into statistics to investigate the probability of failure nor into economic sciences to quantify financial impacts of any damages. The focus here is the fire protection strategy concerning in-house cabling. 3.3 Cable Fire Performance Cables are important elements in fire protection concepts of buildings. There are different kinds of ingredients which increase the fire performance of cable compounds. Halogenated polymers are self-extinguishing by chemical reactions, but in case of fire they generate toxic gases. Halogens are elements of the 7 th principal group: Cl, Fl, Br, J. In the oxidation process they react to acid radicals, which generate acids by reaction with hydrogen. When halogens are burning at low temperatures, dioxins are generated. The consequences of personal injury or damage of goods are described above. Halogen-free flame retardants, for example Mg(OH) 2 or Al(OH) 3 , prevent fire propagation by catching oxygen. The chemical reaction generates water which gives an additional extinguishing and cooling effect. These mineralic flame retardants generate very little smoke when burning, and the fumes are non-toxic and contain no acids.

❍ ❍ Figure 3 : Test set-up flame propagation

Several cable fire-testing procedures are defined by national and international standardisation bodies. Each of them alone represents just one of the different threats of fire. An overview is given in Table 1 . 3.3.1 Self Ignition Cables should be designed in a proper way so that neither voltage peaks nor high ampacity should lead to self- ignition. Voltage and ampacity testing determines the ability of a cable regarding self-ignition. The parameter self-ignition is connected to the probability of fire. 3.3.2 Flame Propagation Cables are connecting devices. So cables carry the threat that a fire may propagate along the cable from one building part into another. This is the effect of a fuse cord. To determine the flame propagation (or fuse cord) properties of cables, IEC 60332 defines test methods on several levels (eg IEC 60332-1-2, Figure 3 ). The common idea of all these tests is the same: a burning cable in a defined position shall extinguish before the flame has propagated a specified distance. The sample position may be horizontal or vertical, and the sample may be a single cable or a cable bundle. Flame propagation parameters are related to both fire avoidance Especially for cables used in fire protection application there are specific fire resistance requirements defined in IEC 60331. This means a cable in a fire shall maintain its function at least for a defined time. These cable types are used, as an example, for fire exit lighting, alarm and warning devices and similar purposes. and impact reduction. 3.3.3 Fire Resistance

Impact reduction

Parameter

Avoidance

Self-ignition

X X

–

Flame propagation

X X X X

Fire resistance

(X)

Smoke exhaustion

– –

Halogen free

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Wire & Cable ASIA – January/February 2016