8. Describe the safety requirements for the electrical installation in a large locker on deck, designated for the carriage of petrol, or vehicles with fuel in their tanks.(10)
Safety Requirements for the Electrical Installation in a Large Locker on Deck Designated for the Carriage of Petrol or Vehicles with Fuel in Their Tanks (10 marks)
1. Hazard classification (1 mark)
- The interior of such a locker is classified as a hazardous area (Zone 1 or Zone 2) because flammable vapours may be present under normal or abnormal conditions.
- All electrical fittings and wiring within or adjacent to the locker must therefore be suitable for use in a flammable atmosphere.
2. Type of electrical equipment (2 marks)
- Only flameproof (Ex-d) or intrinsically safe (Ex-i) electrical equipment may be fitted inside the locker.
- Equipment must comply with IEC 60079 / ATEX standards for explosive gas atmospheres.
- No ordinary or unprotected lighting, switches, or motors are permitted inside the locker.
3. Location of electrical fittings (1 mark)
- Wherever possible, electrical fittings, switches, and junction boxes should be mounted outside the locker, in a non-hazardous area.
- Where fittings must be installed inside, they should be minimised and positioned near the upper part of the locker to reduce exposure to heavier-than-air petrol vapours.
4. Cable type and installation (2 marks)
- All cables passing through or into the locker must be of marine-approved, gas- and oil-resistant, flame-retardant type.
- Cables must be run in sealed, gas-tight conduit or armoured cable to prevent vapour migration along cable routes.
- Cable entries into junction boxes must be flameproof gland fittings or hermetically sealed.
5. Isolation and protection (1 mark)
- The electrical supply to the locker must be fitted with an isolating switch located outside the locker, clearly marked and easily accessible in an emergency.
- Circuits must include over-current protection (fuses or circuit breakers) installed outside the hazardous zone.
6. Earthing and bonding (1 mark)
- The locker and all metallic fittings must be effectively earthed (bonded) to prevent static electricity build-up that could ignite vapours during loading or movement.
- Electrical continuity should be verified at regular intervals.
7. Lighting requirements (1 mark)
- If lighting is required, it must be vapour-proof and flameproof, with well-sealed glands and lenses resistant to impact and heat.
- Alternatively, lighting can be external through a thick, gas-tight viewing window rather than fitted internally.
8. Ventilation interlock and alarms (1 mark)
- Electrical power should only be enabled when mechanical ventilation is operating.
- An interlock system or gas detection alarm should automatically cut off electrical power if vapour concentration exceeds safe limits (below the lower explosive limit).