Well over a decade ago, fires at Browns Ferry Nuclear Plant in Alabama and the World
Trade Centre in New York City focused the attention of cable manufactures and design engineers on the spread of fire through cabling systems. Today’s fire retardant cables are made from specially-formulated, fire-resistant materials. It is around 20 years since the introduction of Reduced Fire Hazard (RFH) cables. This followed the recognition that the waste matter from burning cable materials posed a particular hazard associated with the very common use of halogenated polymeric compounds in the cable construction.
After a number of well known major incidents, initiatives from the MoD, the offshore
industry and the mass transit sectors gave rise to specified requirements, effectively restricting the use of these materials, to minimise the production of smoke and fumes within fire environment. These detailed specifications lead to the establishment of test methods for evaluating cable fire hazards. These detailed specifications and standards were published in 1986 as a British Standard BS 6724 (600/1,000V power cables) and BS 7211 (Building wire) in 1989.
The first cables to be produced were characterised by low smoke evolution, typically eight
times less than the equivalent smoke production from PVC, and also zero or extremely low acidity production. However, though these cables were state of the art at the time, the materials used had some drawbacks, particularly with respect to sheathing compounds. The cables had relatively poor physical characteristics and resulted in a need for maintance and caution during and after installation, which consequently effected on cost.
These developments continued to improve throughout the years and by 1990 the cable
materials were available with a vast improvement on performance. At this time alternative crosslinked low smoke insulation materials also became more widely available and are still used present today. Whilst the materials were being developed over the years, a comprehensive suite of cable performance testing standards had been produced which included requirements for smoke evolution, acidity production, flame retardant and for assessing the circuit integrity of the cables.
This British Standard BS 6387:1994 ( Performance Requirements for cables Required to
Maintain Circuit Integrity under Fire Conditions) specifies the requirements for construction and
performance, and describes methods of test, for armoured fire-resistant cables with thermosetting insulation and of rated voltage 600/1 000 V and low emission of smoke and corrosive gases when affected by fire. 5 The circuit integrity performance under fire conditions is assessed on the basis of various tests which either separately measure resistance to fire, resistance to fire with water, and resistance to fire with mechanical shock, or in combination measure resistance to fire with mechanical shock and water. Cables specified in this standard are intended for use in fixed installations in industrial areas, buildings and similar applications, where maintenance of power supply during a fire is required for a defined period of time. This standards details the following tests to categorise according to their fire withstand capabilities and are cauterised as shown in the table below:
PERFORMA CE TABLE RESISTA CE TO FIRE 650 0C FOR 3 HOURS 750 0C FOR 3 HOURS 950 0C FOR 3 HOURS 950 0C FOR 20 MINUTES RESISTA CE TO FIRE WITH WATER
A B C S
650 0C W RESISTA CE TO FIRE WITH MECHA ICAL SHOCK 650 0C 750 0C 950 0C X Y Z
Pictures attached to this assignment show various of cables with limited fire resistance
which have been exposed to fire under BS 6387 Category C the 3 hour fire test, however to achieve full fire proof status these cables must undergo two further tests, exposure to fire with water spray and exposure