(i) Hazards and problems associated with electric cable insulation in the event of fire:

The insulation of electric cables is typically made from rubber or plastic. The type and quantity of smoke produced during the combustion of plastic materials depend on various factors, such as:

• The nature of the plastic
• The presence of additives
• Whether the fire is flaming or smouldering
• The availability of ventilation

Most plastics decompose when heated, producing dense to very dense smoke. Ventilation may help in dispersing the smoke, but usually not enough to maintain clear visibility. Plastics that burn cleanly emit less dense smoke when subjected to heat and flame.

Urethane foam, when exposed to both flaming and non-flaming heat, generally produces dense smoke, and visibility can be lost within seconds.

Hydrogen chloride, a deadly gas with a pungent and irritating odour, is released during the combustion of chlorine-containing plastics such as PVC—commonly used in electrical wiring insulation.

Burning rubber produces dense, black, oily smoke, which has toxic properties. Two of the harmful gases released in the combustion of rubber are hydrogen sulphide and sulphur dioxide, both of which are dangerous and potentially lethal.

(ii) Remedies for these problems:

• Use cables with Fire-Resistant (FFR) insulation combined with flame-retardant sheathing, such as FEP or XLPE, and stainless steel (SS) armouring.
• The SS armouring must be properly earthed.
• The combustibility of insulation material is assessed by its oxygen index number, which represents the minimum percentage of oxygen required to sustain combustion:
  • Materials with an oxygen index below 21 will continue to burn.
  • Materials with an oxygen index of 27 or above are self-extinguishing.
• Therefore, insulation materials should have an oxygen index greater than 27 to ensure fire resistance.

• All electric cables installed externally to equipment must be of flame-retardant type and installed in a way that preserves their flame-retarding properties.
• Cables and wiring serving essential or emergency power, lighting, internal communications, or signals should, wherever possible, be routed away from high-risk areas such as galleys, laundries, refrigerated cargo (r/c) spaces of category 'A', their casings, and other hazardous zones.
• In hazardous areas where cables could cause fire or explosions during an electrical fault, special precautions must be taken.
• Cables should be installed and supported in a manner that avoids chafing or other physical damage.
• Terminations and joints must maintain the fire-resistant properties of the original cable.
• Every individual circuit should be protected against short-circuiting and overloading.
• When a cable passes through a bulkhead or exits a gland box, a fireproof compression gland must be fitted to prevent the spread of fire.