WCA September 2011

not propagate fire more than a limited distance from the source. Such cables have been well established in the market since the 1970s for cabling in areas where, because of installation conditions, eg vertically mounted bunched cables, the risk of propagation of fire is high. They are tested to the various parts of IEC60332-3. Low smoke cables which have limits on smoke evolution when assessed in the 3m cube smoke chamber with performance limits chosen to give visibility over 10m distance. They were introduced because cables containing conventional sheathing materials based on PVC were seen to give off large amounts of dense smoke when affected by fire. Such cables have been manufactured since the 1970s, but it was not until advances were made in cable making material technology in the 1980s that cost effective designs became widely available on the market. They are tested to IEC61034-2. Generally cables of this type also combine the properties of low corrosive gas emission and are manufactured using “halogen free” materials. Low corrosive gas emission cables which have limits on acid and corrosive gas emission when assessed by burning samples of materials in a bench tube furnace. They were first introduced when users began to raise concern over the large amounts of acid gas emissions from burning reduced propagation PVC cables. This corrosive and irritant gas had been seen to have devastating effects on electrical panels and instrumentation exposed to cable fire effluent (9,10) .

The cable industry also was aware that it would need to develop its own tests to properly assess the performance of its products. Although this early development led to a series of tests that could be said to lack integration, the approach when taken as a whole still sits well with current thinking. Another important consideration was that large scale tests should be developed wherever relevant so as to assess performance of the total product in something approaching an “as installed” condition. The international work concentrated on the development of test methods so that these could be adopted as an “add on” to product standards such that the widest possible levels of fire performance could be achieved across the full range of product types. Current Situation The relevant IEC test standards have remained largely unchanged over recent years but have been subject to ongoing refinement (5,6,7,8) . For example, IEC 332-3 has developed into a multipart standard with each part covering a different installation condition or time of exposure to the fire source. The principles established in the early development of these standards still serve cable manufacturers and users well and the IEC standards are adopted in many countries. Based on the use of these tests, one can find in the market various types of cables. Reduced flame propagation (RP) cables which when installed in vertical bunches in accordance with the recommended procedures do

❍ ❍ Figure 2 : prEN50399 apparatus

❍ ❍ Figure 3 : Typical SPR and HHR curves

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