DOSSIER

 

Reducing the risk of fire in the engine room(I)


Considering the wide range of both sources of fuel and sources of ignition within the engine room, it should come as little surprise that a large proportion of fires onboard ships originate there.

Research coordinated by IMO1 has indicated that between 30 and 50% of all fires on merchant ships originate in the engine room and 70% of those fires are caused by oil leaks from pressurised systems. Following a major engine room fire it is relatively rare that a ship is able to proceed under her own power. This leads to expensive costs of salvage, towage, repairs, downtime, cancellation of cruises, etc, which can typically run into millions of dollars.

Special attention should be given towards maintaining a clean and tidy engine room where machinery and emergency control equipment are installed and operated in accordance with SOLAS Regulations and IMO Guidelines and that the equipment is routinely serviced and maintained in good working order, and subject to routine testing. IMO MSC.1 /Circ. 1321 dated 11 June 2009 entitled “Guidelines for measures to prevent fires in engine rooms and cargo pump-rooms” is especially relevant. If a failure to carry out proper maintenance or to have proper maintenance systems in place is linked to the cause of a fire, the shipowners or managers could face litigation in which allegations of crew negligence and/or unseaworthiness feature.

Except in certain specialist ships, the engine room is invariably a large enclosed space with limited divisions and compartmentation, with restricted access and with only defined walkways between equipment. It is not surprising, therefore, that engine room fires often present very challenging fire fighting conditions where effective first-hand. Ffire fighting may be limited in time for reasons of safety, and where visiting fire parties may have to fight the fire from above when there is little or no visibility. Frequent and realistic fire drills that are tailored to address foreseeable fire scenarios specific to the particular engine room are essential. Moreover, some ship operators choose to engage specialist fire training companies to provide more advanced training aboard their ships.


Fire essentials


All seamen should be aware of the Fire Triangle principle in that if the three elements of an oxidiser, (invariably oxygen from air), a source of fuel and a viable source of ignition come together a fire will result. The basic principles of fire fighting are to “break” one or more sides of the Fire Triangle so as to limit or eliminate the source of fuel and/or the oxidiser. It is also important to keep the fire triangle in mind when conducting fire risk assessments and implementing fire prevention measures.

In an engine room there is inevitably a plentiful supply of air and very effective ventilation systems. It is helpful, however, to consider in a little more detail the other two elements of the fire triangle; ‘sources of ignition’ and ‘fuels’. An appreciation of the ignition processes will enable engine room personnel to better implement fire risk assessments and fire prevention measures.


Ignition processes


The process of ignition involves the transfer of a sufficient amount of energy to a fuel to initiate a self-sustained combustion reaction. Not all potential sources of ignition will be viable for all types of fuel. For example, whereas a short duration electrical spark is likely to be a viable source of ignition for flammable gases, it will not ignite a liquid fuel unless it is very hot (above its flash point) nor would it ignite most solids. Similarly, although hot particles produced from welding or cutting operations (including angle grinding and disc cutting) are capable of initiating a smouldering fire in fibrous or finely divided solid fuels such as cotton waste, cotton rags, sawdust and cardboard packaging, such sources of ignition are much less likely to ignite solid materials such as timber and plastics. It should be noted that carelessly discarded smokers’ materials (such as cigarettes and matches) provide a potent source of ignition for materials capable of supporting a smouldering fire. Smoking in an engine room should be confined to the control room, where appropriate means of disposing smokers’ waste materials should be provided, such as a sand tray or a suitable safety ashtray. On no account should smokers’ waste materials be disposed of in a general waste container, such as a waste paper bin.

It will be apparent from these considerations that sources of fuel and potential sources of ignition cannot be considered independently from one another. Possible fuels in an engine room exist in the solid, liquid and gaseous states and their physical and chemical properties will determine the way in which they react to a potential source of ignition and whether that ignition source is viable. The table in Appendix 1 summarises the various types of fuel typically encountered, conditions required to achieve ignition and examples of viable sources of ignition for the fuel. For ease of reference the technical terms shown in italics in the table are explained in a glossary.

Although the table in Appendix 1 provides a useful and quick source of reference, it is helpful to illustrate how a failure to comply with SOLAS Regulations and to provide for effective maintenance and tidiness in an engine room can lead to a serious fire with the potential for loss of life and injury, major financial consequences and unnecessary litigation.


Oil fires


Oil fires are invariably the most serious category of engine room fires. Two ships entered with the Club recently suffered significant engine room fires with remarkable similarities. Both fires originated in the region of the generators when leaking oil sprayed onto hot exhaust surfaces and the subsequent efforts to extinguish the fires were hindered because of a failure to maintain the fire smothering systems correctly and/or a lack of understanding by the crew of the correct method of deploying the systems. In one case, two crew members suffered smoke inhalation injuries and in the other, one died while trying to fight the fire. In both cases significant damage to the engine room occurred resulting in towage and expensive repairs.

Fires can result from a failure to attend to small persistent leaks that can, for example, spread across machinery surfaces to reach parts operating at a high temperature, and from larger leaks that develop suddenly. For example those caused by:

  • Loose joints
  • Fractured pipes and mechanically damaged (perforated) pipes on both high and low pressure fuel lines
  • Bleed cocks on generator fuel filters working loose
  • Pipe unions that are over or under tightened
  • The fracture of flange bolts if over tightened
  • The fracture of cyclically stressed bolts or studs that are under-tightened, such as those securing fuel injector pumps
  • The use of unsuitable seals or gaskets which deteriorate due to the effects of heat
  • The rupture of high pressure oil and hydraulic fluid hoses due to mechanical damage or aging

Correct maintenance procedures should be strictly adhered to. High pressure pipes should be sheathed and flange joints enclosed where they are in proximity to hot surfaces in order to comply with SOLAS Regulations. Any hot surface shielding should also be effectively maintained.

Hot surface ignition and preventative measures

 

Oil fires usually occur when oil from a large leak or a smaller but persistent leak comes into contact with a nearby hot surface at a temperature that exceeds the ‘minimum auto ignition temperature’(MAIT) of the oil. MAITs of diesel and fuel oil are typically about 250°C, but MAITs as low as 225°C have been reported. Lube oils and hydraulic oils have somewhat higher MAITs. High pressure sprays comprising fine droplets of oil can ignite immediately on contact with the hot surface, and liquid leaks can ignite after a short period of time sufficient to evaporate the oil and generate a flammable concentration of fuel vapour. Under certain circumstances, such as where flammable concentrations of vapour form in confined spaces, the fire may be preceded by an explosion. Clearly, all oils should remain contained within their intended systems. Oil fires often develop and spread quickly compromising the safety of engine room personnel and, in the case of generators, damaging associated main electrical cabling feeding the switchboard which can lead to a loss of electrical power and, as a result, motive power.

Spray shields should be fitted around flanged joints, flanged bonnets and any other threaded connections in fuel oil piping systems under pressure exceeding 0.18 N/mm2 which are located above or near units of high temperature in accordance with SOLAS II-2 Reg. 4.2.2.5.3 and MSC.1 /Circ1 321. Furthermore, high pressure fuel delivery pipes should be sheathed within jackets capable of containing leaks from pipe failures, the annular spaces of which must be equipped with suitable drainage arrangements to facilitate the rapid drainage of oil to a safe location, such as a drain tank.

It is essential to employ good maintenance systems and engineering principles in order to reduce the risk of oil leaks. This includes, for example:

  • attending to minor leaks without delay
  • tightening connections to fuel injectors and fuel injection pumps to the correct torque to prevent leakage and/or fatigue fractures caused by cyclical stresses induced by operation of the pump
  • maintaining oil leak detection and alarm equipment that can warn of the presence of oil leaks in concealed areas such as a ‘hot box’ enclosing fuel pumps on some types of generator

Potential route for hot oil vapour to spread from the hot box enclosure to the exhaust enclosure (cladding/covers removed for inspection)

The maintenance of leak detection/alarm equipment is especially important where oil vapour from a leak of hot oil at a temperature above its flashpoint can, for example, migrate from the hot box of a generator, across the engine entablature to exhaust system enclosures where the vapour can auto-ignite on exhaust components that are otherwise properly shielded from leaks in accordance with the requirements of SOLAS.

Preventing oil leaks is one half of the problem, the other being effective cladding or shielding of hot surfaces so that they do not present a source of ignition if an oil leak occurs. This is possibly the most effective way to prevent Engine Room fires and fairly easy to implement onboard.

It is a SOLAS requirement that surfaces, with temperatures above 220°C that might come into contact with oil as a result of a system failure are properly insulated. Ship’s crew should, therefore, appreciate that even a small exposed area of no insulated hot surface, such as part of a flange joint or an instrument pipe, can be potentially dangerous. The photographs below illustrate examples of defective protection of hot surfaces ranging from a complete failure to clad generator exhausts to the exposure of parts of exhaust systems.

While every effort may be made to shield or clad large hot surfaces and their appendages, gaps can exist even in what appears to be well maintained insulation. Turbochargers, in particular, by their complex shape canbe particularly challenging to effectively insulate. Therefore, it is sensible practice to carry out routine surface temperature measurements of the critical parts of machinery, especially at bends and flange joints where surface profiles may vary considerably. This can be done effectively by using an Infra­red temperature gun (such as the one illustrated) which is relatively cheap and provides an instantaneous visible reading while being used remotely from the area of interest. It is important to follow the instrument manufacturers’ operation instructions otherwise misleading results will be obtained. Some instruments sound an alarm if a measured temperature is outside set limits. It should be noted that higher surfaces temperatures are likely to be reached when there are higher ambient temperatures (such as when the ship is operating in hotter climates) and engines should be under normal or heavy load and up to maximum operating temperature when measurements are made. The instrument can also be used to warn of potential sites of localized electrical overheating on the main electrical switchboard, electrical circuitry and running machinery and for the correct operation of reefer equipment, as will be discussed later.

 

Alternatively, surveys can be carried out by using more expensive thermal imaging equipment which provides a clear image of the surface temperature profile as illustrated in the example below, where the thermal image is compared with the visible light image.
Uncovered indicator cock with exposed temperature above SOLAS limit
IR001153.IS2-NO1 Auxiliary engine

 

Lagging fires

Visible light image Main image markers

 

 

 

 

 

 

 

 

Emissivity

As a result of such surveys, it was estimated that around 80% of ships checked had exposed areas in excess of the 220°C SOLAS requirement. Recent checks by the Club’s Risk Assessors using an Infra-red temperature gun suggest that this figure may not be exaggerated.

Indicator cocks are another potential source of ignition. IMO MSC.1 /Circ. 1321 Para 1.1.5 recommends that “Exposed indicator cocks should be insulated in order to cover the high temperature surface.”

Again, an IR temperature gun can be used to assess the fire ignition risk of uncovered indicator cocks.

If mineral oils (fuel oil, diesel oil, lube oil) soak into lagging on pipe work operating at a temperature above about 150°C there is a risk that the oil will oxidise slowly within the matrix of the lagging and eventually ignite spontaneously, causing the lagging to disintegrate and oil from a persistent leak to ignite. This process can take many hours, and there may be little external warning of the imminent danger until smoke appears shortly before the fire becomes visible. It is essential, therefore, that oil leaks are attended to promptly and that permanent repairs, including the replacement of oily lagging, are made correctly rather than resorting to makeshift solutions.


Risk of‘spontaneous ignition

 

Tank save-alls
Dirty oil tanks and purifier save-alls present a fire hazard, both from being at a risk of ignition and providing a means of spreading a fire. It is essential to keep drain lines clear and prevent oil accumulation. Oil residues are likely to be at a temperature below their flash points and, therefore, not directly ignitable. However, fibrous solids such as cotton waste and rags partially immersed in the oil can function as a wick. The ‘wick’ may be ignited by contact with a welding spark or a smouldering source, such as a carelessly discarded cigarette, leading to a smouldering fire that eventually undergoes transition to flame. The oil feeds into the wick to sustain the fire and the surrounding oil layer is raised to a temperature at which flame can spread across the oil surface causing the fire to develop. The failure of tank valves and level gauges directly exposed to the save-all fire becomes possible.

Self-closing valves are fitted between the lower end of an oil tank and its gauge glass. The purpose of these valves is to isolate the tank gauge glass from the tank. In normal operation they should be shut and only opened to check the tank contents after which they should be shut automatically under spring pressure or counter balance gravity.

The UK Club’s ship inspectors regularly find that various methods are used to keep these valves permanently in the open position. Chocks of wood, pieces of wire and purpose made clamps are often seen to be used to for this purpose. This is dangerous practice. If a gauge glass breaks in a fire the entire contents of the tank will leak into the burning area, escalating the fire.

 

 

Solid fuels
As summarised in the Table at Appendix 1, solid fuels typically encountered in an engine room include:

- cellulosic materials, such as constructional timber, cardboard packaging, sawdust, cotton waste and rags, and

plastic materials, of which there are two main types: thermosetting plastics, which maintain their form and rigidity - when exposed to high temperatures, and thermoplastics, which tend to melt and drip when exposed to high temperatures.

 

The potential for cellulosic materials to smoulder and to be susceptible to ignition by small ignition sources such as sparks produced by hot work and carelessly discarded smokers’ materials is often overlooked. Smouldering fires can develop slowly, sometimes in concealed spaces, and may not be discovered until several hours later after the transition from smouldering to flaming combustion has occurred. Although the presence of constructional timber in an engine room is unusual, it should be noted that timber insulated from its surroundings and in contact with a hot surface at only a moderately elevated temperature (i.e. above about 120°C) can under certain circumstances ignite after many days. Any constructional timber should, therefore, be well separated from or insulated from hot surfaces.
Angle grinding and disc cutting operations should be included in the ‘hot work’ category because, although the size of incandescent particles produced is generally very much smaller than those produced by welding and flame cutting operations, a stream of grinding or disc cutting sparks landing in the same area of a solid fuel can be sufficient to initiate a smouldering fire. Frictional heating of the work piece may also act as an ignition source, e.g. of oil residues on its surface.

 

It is essential that engine room workshops and stores are kept clean and tidy and that smoking is strictly prohibited. In the stores, packaging materials should be kept to a minimum and cardboard cartons should be stored clear of light fittings. In the workshop, floor areas and work surfaces should be clear of all combustible waste, particularly cellulosic materials susceptible to smouldering combustion. This is especially important when hot work is carried out behind welding curtains to prevent the spread of stray sparks. Cotton waste and rags should be kept in a bin fitted with a lid and bales of cotton waste and rags stored in a metal cabinet.

Oil soaked rags have been known to “self heat” and combust spontaneously so, until they can properly be disposed of, should be kept in a steel container with a lid.

Hot work outside the workshop should be the subject of a hot-work permit system. It should be noted that sparks from welding and flame cutting operations take time to cool to a temperature at which they are no longer incendive, can be projected considerable distances, e.g. more than 10 metres, can travel horizontally by bouncing and can fall though gaps. Careful consideration must be given to the removal of all combustible materials within range of the hot work and the use of proprietary welding blankets or curtains to cover materials that cannot be moved and to cover any gaps to prevent incendive particles falling into unprotected areas. If there is a possibility of a flammable atmosphere being present in the area where hot work is planned, gas testing of the atmosphere within range of flying sparks must be carried out before and frequently during the work out by a competent person using an explosimeter that has been calibrated and serviced in accordance with the instrument manufacturers’ guidelines. Hot work should only be permitted if the reading on the explosimeter registers 10% LEL or less both before and during the hot work.

Another potential source of ignition is an electrical lead light whose unprotected bulb and its filament are perfectly capable of starting a fire.

 

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