Scavenge fire is one of the most common reasons for a fire in a ship's engine room.
Scavenge fire has been the reason for several major accidents on ships in the past and is termed as the most dangerous cause for accidents onboard.
Causes of scavenge fire:
- Excessive wear of the liner
- The piston rings worn out or having loose ring grooves
- Broken piston rings or rings seized in the grooves
- Dirty scavenge space
- Poor combustion due to leaking fuel valves or improper timing
- Insufficient or excess cylinder lubrication
Indications of scavenge fire
There are a few signs which indicates a scavenge fire. One should be extremely cautious in case any of the below mentioned conditions are observed.
- Scavenge temperature will start increasing
- The turbochargers will start surging
- High exhaust temperature
- Loss of engine power and reduction in RPM. This happens because back pressure is created under the piston space due to fire
- Smoke coming out of the scavenge drains
- The paint blisters will be formed on the scavenge doors due to high temperature, but this will occur only in large fires and extreme cases
Actions to be taken
Action taken in case of a scavenge fire depends on the type of the fire, whether small or large. In case of large fire the following signs will be easily visible - the peeling or blistering of paint, large reduction in engine RPM and surging of turbocharger.
For small fires:
- Start reducing the engine rpm and reduce it to slow or dead slow
- Increase the cylinder lubrication of the affected unit. Special attention to be given to avoid that lubrication does not feed the fire. In case of increase of fire do not increase the lubrication
- The fire can be due to leaky fuel valves, so lift up the pump of the affected unit
- Keep scavenge drain closed
- Keep monitoring the scavenge and exhaust temperatures and let the fire starve and wait for it to burn itself out
- After confirming that the fire is out, start increasing the RPM slowly
- Keep monitoring the scavenge temperature for any signs of re-ignition
For large fires:
- Stop the engine immediately and engage turning gear, and keep engine rotating with turning gear
- Extinguish the fire with fixed fighting system for scavenge fire. This may be C02 system or a steam connection for smothering the fire
- If steam system is installed, ensure to drain the line before injecting steam, as condensed water, which is at low temperature inside the steam pipe ,will go to engine cylinder causing thermal distortion
- In case fixed system is not available on very old ships an external cooling is provided to prevent distortion due to heat
- Once after confirming that the fire is extinguished, the scavenge space is allowed to cool down and later opened for inspection and cleaning of the scavenge space
References
A Pocket Guide To Fixed Fire Fighting Systems and Emergency Procedures For Ship’s Engine Room (Author: Marine Insight)
