To reduce fire hazards in case of a leak in the high-pressure (HP) fuel line (between the fuel pump and injector), jacketed fuel pipes are used for HP fuel delivery lines. If there is a leak, the heated fuel may escape as a jet or spray which, upon contacting a hot surface, could ignite. However, in a jacketed fuel line, any leaked fuel is safely routed away through an outer casing.

In MAN B&W type engines, each fuel pump’s high-pressure jacketed leak-off space is connected via a drain line to a common drain tank. This tank includes a level switch and an overflow pipe with a small drain bore below it.

• Minor leakages: The small drain bore allows the oil to escape without activating the level switch.
• Major leakages or pipe fracture: The bore will be insufficient to drain the larger oil volume, causing the oil level in the tank to rise. Once it reaches the level of the overflow pipe, the level switch is actuated, triggering an alarm.

As per SOLAS Chapter II-2, Regulation 4.7.1, in ships with periodically unattended machinery spaces, provisions must be made for early detection and alarm in case of fire in scavenge spaces.

While the regulation does not specify a temperature for alarm activation, engine makers typically set the alarm at 80°C.

• A temperature sensor is installed in the scavenge air belt.
• This sensor is connected to the machinery space alarm panel.
• When the set temperature is reached, an alarm is triggered to alert the crew to the imminence or possibility of a scavenge fire.

According to SOLAS Chapter II-2, Regulation 4.7.2, for ships operating under UMS conditions:

• Internal combustion engines of 2250 kW and above, and having a bore diameter of 300 mm or more, must be fitted with:
  • Crankcase oil mist detectors
  • Engine bearing temperature monitors
  • Or equivalent monitoring devices

  These are essential for monitoring conditions that may lead to a crankcase explosion.

  A crankcase oil mist detector, based on the photoelectric principle, operates as follows:

  • A bulb emits light, which is reflected by mirrors onto two tubes:
    • One is the reference tube
    • The other is the measuring tube
  • Crankcase gas samples from each unit are directed into the measuring tube.
  • The photoelectric cells compare the light signals from both tubes.
  • If there is oil mist in the gas, the difference in signal activates an alarm.