Germany's latest emergency tug can continue operations and accept casualties into its hospital even when the surrounding atmosphere contains toxic or flammable gases as a result of fire or explosion from the large cargo ships it is designed to rescue.
'Nordic' has two citadel areas that can be maintained at an overpressure to exclude potentially harmful gases. These areas cover the vessel's hospital as well as the bridge, engine control room and other key accommodation and deck spaces. Airlocks provide access so that rescuers can still bring in stretchers and a plug-in system on deck enables deck crew wearing breathing apparatus to rest and draw in air from the ship's system if required.
A bank of compressed air tanks maintains the over-pressure, and the tug can operate for at least eight hours before having to withdraw and recharge with fresh air. This arrangement was chosen because the alternative, a more typical air filter system, may not be suitable for every possible type of toxic substance the tug may encounter and would delay the safe entry of the vessel into a hazardous situation while the gases are analysed.
The vessel's twin-screw propulsion system is powered by two MTU 20V8000 M71L GSB diesel engines that can operate in hazardous atmospheres. MTU was chosen as the only provider that could achieve the performance required in atmosphere-independent gas-protected operation mode, though the power output of the engines is still reduced from 8,600kW to 4,000kW in this mode.
The ship automation system, MTU's Callosum, monitors the main and auxiliary engines and controls the transition to gas-protected operation if required. Sensors monitor critical parameters such as the air temperature after compression, which must not be allowed to rise above 135 degrees Celsius. If this occurs, engine power is reduced and intake air and exhaust gases are cooled. The automation system also monitors cylinder-firing so no unburned gas and air mixture enters the exhaust system where it could easily ignite in contact with hot surfaces. The engine is fitted with a flame arrester and emergency air shut-off flaps in the charge air duct. These cut the air supply quickly if emergency shutdown is required.
The onboard power supply is provided by two shaft generators from Leroy Somer, with 12V 4000 M50A diesel engines capable of a power output of 1,140kW. These engines are also able to operate in gas-protected mode. An emergency generator powered by a MAN diesel and an additional auxiliary generator is provide power when the vessel is at anchor and the main auxiliaries are shut down.
Draeger Safety played a key role in the installation of the atmosphere-independent systems on board 'Nordic' including the provision of a network of hazard detection sensors and pressure monitoring equipment.
'Nordic' was delivered from shipyard P+S Werften and commenced operation early this year. The 78-metre vessel was designed by Skipskonsulent of Norway, classed by Germanisher Lloyd and is the result of ten years of planning and project management by three German tug operators and salvors: Bugsier, Fairplay Towage and Unterweser Reederei. The vessel is yet to be involved in a rescue operation but also functions as a training vessel.
Wendy Laursen