Industrial Fire Journal - Fire & Rescue - Hemming Group Ltd
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High pressure success for total engine flooding
Published:  01 October, 2008

High-pressure water mist systems are now widely accepted as an excellent alternative to the controversial CO2 or other gas-based systems for fire fighting in engine rooms, including total flooding and local application systems.

Fast-response, low-cost local application systems have already proven their cost-effectiveness in several cases where this system has prevented fires from spreading, rapidly controlling or often extinguishing the fire before any major damage has occurred.
Before local application systems were implemented, crews were often reluctant to activate CO2 or other gas systems, giving fires more time to develop and causing more damage.


With the introduction of high-pressure water mist local application systems, the low water consumption allowed “live drills” to be carried out, with water actually being released. The crew could then become fully familiar with the system and, in the event of a real fire, would not hesitate to activate the system. This is even possible with personnel in the engine room itself. As a consequence, there is no need to waste valuable time waiting to muster the engine crew in a safe area, as is the case with gas systems. In contrast, fire fighting can be instantaneous, leading to quicker control of the fire, significantly less damage and lower costs.


Currently, the existing main total flooding system would usually be a CO2 or other gas system. However, it is now possible to use water mist for the entire total flood system, and not just for localised applications.


Over the course of extensive live trials and actual installations, high-pressure water mist systems have proved themselves extremely effective, both economically and in terms of fire suppression, in accordance with the demands of MSC 668. The excellent results achieved by high-pressure water mist systems in local applications, together with growing demands from safety-conscious owners, consultants and yards, has led to an ever-increasing demand for high-pressure water mist systems to be deployed in a total flood context as an alternative to the various gas systems on offer.


Unfortunately, the previous MSC 668 regulations only allowed for smaller engine rooms to be protected by water mist. However, this standard has now been revised to MSC 1165, which allows for deployment in larger engine rooms; albeit in practice only up to 4 to 5,000 m3, which does not yet allow ship owners to exploit the full potential of a Danfoss Semco high-pressure water mist systems. However, for these smaller engine rooms, we are already seeing a marked increase in demand for Danfoss Semco water mist systems to provide both local application and total flood fire protection.


Danish ship owner Esvagt was looking for an effective and economical fire fighting system for engine room protection for their new multirole emergency response rescue vessels, under construction in Spain. Esvagt rigorously examined and tested all available solutions, including CO2 and other gas systems – for local applications and total flood – both singly and in various combinations, including using a mix of gas and water mist. In the event, the CTO of Esvagt opted for a comprehensive Danfoss Semco high-pressure water mist system for all applications.


In the course of their extremely detailed analyses, Esvagt examined every possible factor that could potentially lead to a system failure.


As a result of their deliberations, they decided to go way beyond the one-minute pressure tank back-up demanded by the existing MSC 668 regulations. It was eventually decided to specify a full ten-minute system back-up, to allow for potential power supply failure or the delayed start-up of the emergency diesel generator.


Three options for the design and construction of this back-up system were comprehensively reviewed:


1. the use of additional high-pressure cylinders using nitrogen as a propellant
2. the installation of a gas pump/turbine, again using nitrogen as a propellant
3. the installation of an additional pump, outside the engine room, driven by diesel.

Option 1 was rejected due to both the excessive weight of the solution and the difficulty of finding a suitable location for the multiple high-pressure cylinders it required. Another issue was the problem of maintaining and servicing the cylinders, which required easy access and the ability to transport them to a workshop for pressure testing.


Option 2 was rejected for much the same reasons, as it required too many high-pressure nitrogen cylinders and too much maintenance of specialised equipment, in addition to regular pressure testing. A further drawback was that testing was not possible without the actual consumption of nitrogen, which is costly and difficult to replace.


Option 3 proved to be the preferred solution. The direct diesel-driven pump satisfied both the class (DNV) requirements and those of the owner, as well as being a technically satisfactory solution from the yard’s perspective. This was due to the fact that a diesel is light in weight compared to cylinders, as well as being familiar to crews and easy to maintain. The other deciding factor was that it is easy to perform regular system tests, which only involved the consumption of negligible amounts of diesel.


It was decided to locate the diesel-powered pump adjacent to the emergency diesel generator room, with its own water and diesel tanks. The water tank was to serve as an emergency reservoir, containing enough water to supply the system at full deployment for approximately ten minutes. As necessary, the solution also allowed for the possibility of refilling with either fresh water or sea water. In addition, the diesel unit functioned as a redundant pump unit, supporting the main electrical pump in the event of problems other than a power failure.


The diesel-driven pump unit was attached to the main system via a single pipe fitted with a non-return valve. The system was designed to allow testing of the diesel unit either with or without actually releasing water into the engine room.
The diesel unit is activated from a compartment on the upper deck via a push button that activates the electrical starter, which is served by dedicated batteries under constant charge.

Further observations


Safety-conscious owners and operators are increasingly asking for high-pressure water mist systems to be installed to provide total flooding fire protection in engine rooms. However, the practical limit of approximately 4-5,000m3 set by the current MSC 1165 regulations restricts the implementation of high-pressure water mist systems as a substitute for CO2 and other gas-based solutions. Fortunately, the regulators are currently working on ways to expand the volumes at which high-pressure water mist can be permitted to serve as a total flooding agent.


One initiative already under way is the IWMA project for developing and testing a scaling model, to assess the volume potential of water mist systems. Another project is the development of a system and test specification for allowing water mist systems to be “zoned” in engine room compartments. Zoned systems allow for larger engine rooms to be equipped with high-pressure water mist, without placing excessive power or pressure demands on the system.

Conclusion


The excellent results achieved by high-pressure water mist systems in engine rooms, in both local and total flood applications, is providing strong impetus for their development for use in ever-larger engine spaces. This increase in interest is entirely a result of the system’s outstanding functional and logistical advantages, which include:


• extremely rapid response to a fire incident, resulting in greatly reduced fire damage
• excellent cooling effects, enabling personnel to approach the fire area and enhance fire fighting activity
• very efficient use of water, in minute droplets, which both greatly increases fire fighting effectiveness and significantly reduces collateral water damage
• a harmless cooling agent – water – which allows safe and cheap drills to take place, ensuring that personnel are fully familiar with the system
• ease of installation, using small-bore pipes and pre-assembled power units.