Fire in the galley duct
Published: 01 October, 2008
In ships and marine technology fire extinguishing systems for protection of galley deep-fat cooking equipment are becoming particularly popular. Over the past 10 years the use of more efficient cooking appliances and the increased use of vegetable cooking oils has increased the level of risk. Heating cooking oil to its auto-ignition temperature (around 365 °C) can lead to a very intense fire that is very difficult to extinguish and which can involve the inside of the hood and exhaust duct – usually covered with grease and dust – resulting in an uncontrolled fire in the galley area.
According to Solas Chapter II-2, Reg 10.6.4, deep-fat cooking equipment should be fitted with:
• an automatic or manual fire-extinguishing system tested to an international standard acceptable to the organization (eg ISO 15371.2000)
• a primary and back-up thermostat with an alarm to alert the operator in the event of failure of either thermostat
• arrangements for automatically shutting off the electrical power upon activation of the fire-extinguishing system
• an alarm for indicating operation of the fire-extinguishing system in the galley where the equipment is installed
• controls for manual operation of the fire-extinguishing system which are clearly labeled for ready use by the crew.
Furthermore, according to Solas Chapter II-2, Reg 188.8.131.52, in passengers ships carrying more than 36 passengers, exhaust ducts from galley ranges should be fitted with a fixed means for extinguishing a fire within the duct.
In order to achieve the relevant Type Approvals by Maritime Authorities such as RINa, BV, the R&D group at Eusebi Impianti has carried out intense testing to develop two concepts of the EI-Fog high pressure water mist system that are compliant with the internationally recognized fire test protocols (ie ISO 15371.2000 for DFF (deep fat fryers) and UL 300 for galley exhaust ducts).
ISO 15371.2000 – for example – outlines that the vegetable oil fires in DFF should be extinguished without any re-ignition and also avoiding oil spread during the extinguishing medium discharge phase that could lead to operators being injured. Although this is extremely challenging, the cooling capability of the very small droplets produced by the EI-Fog system has been demonstrated to be an optimal solution for this particular application.
A number of full-scale fire tests were carried out to demonstrate the fire extinguishing capability of the water mist system in a galley duct. In one test, typical high-flashpoint cooking oil/grease was sprayed onto the inner surfaces of a duct.
The objective of the test was to demonstrate the extinguishing speed of water mist when used with a fully developed fire. The fire scenario simulated a worst-case accident in which other fire protection measures had failed – typically a duct fire originates from a fire in a deep fat fryer. During the extinguishing test, the gas temperatures everywhere in the duct dropped sharply upon activation of the water mist system, indicating fast extinguishment of the fire. In particular, it should be noted that the temperatures at further locations did not increase again, indicating that the fire did not spread in the duct.
Upon activation, that the fire was extinguished was proved by the sharp decrease in temperature – and in no test did the temperature rise again anywhere. Small residual flames self-extinguished with no additional application of extinguishing agent. At the end of the test, the duct was checked for presence of grease, to ensure that the fire had not self extinguished.
The two applications demonstrated how the small droplets of water mist system can be highly effective in extinguishing intense fires and:
• use very small amount of water;
• extinguish vegetable oil fires without causing splash;
• are effective in local application areas (DFF) as well as narrow spaces (exhaust ducts);
• are not intrusive (being only a connection from the accommodation spaces EI-Fog water mist system or a small self-contained system if required in certain circumstances);
• can be activated by the crew without any training.