Fire and gas detection
Modern ships may not be made of easily flammable wood, but fire is still one of the most feared events onboard a ship. Although a ship afloat is surrounded by the means to fight most fires, the construction of a ship and the flammable and explosive material that may be on board make fire-fighting a very hazardous venture. Prevention and detection is therefore of the utmost importance.
SOLAS requires regular checks for fire which today is mostly done by automatic systems of various types instead of the traditional means of fire patrols, but very often a fire will be discovered by a crewman or passenger before an automatic alarm system activates. For this reason it is important that manual fire alarm points are strategically located throughout the vessel and their locations well signed. Fire patrols are still required by some administrations even if automatic systems are fitted. Engine rooms, personal cabins and cargo spaces are where most fires begin.
Fire detection systems are compulsory in ships that have periodically unattended machinery spaces. In addition to the general fire alarm system, there are other devices on board that will alert crew when a situation that could lead to a fire or explosion is occurring. Temperature sensors on machinery and oil mist detectors fitted to the main engine both fall into this category. So too do gas detectors that can monitor the build-up of explosive gases from oil and gas cargoes.
The vast majority of fire detection and alarm systems are those which make use of detectors and call points. Detectors are usually of three types sensing heat, smoke or flame. The first is by means of temperature sensors, the second by an ion chamber and the third by using infrared light to detect flicker patterns caused by flames.
For cargo holds, a different type of smoke detection is used. Sampling smoke detectors draw air from the cargo hold continually using fans and a pipework system that can also be used to send CO2 gas to extinguish a fire in the hold. In the smoke detection system, the air is tested for smoke and other combustion products before being vented to air.
A fire detection system can be in one of two configurations. These are usually described as conventional or addressable with the latter being able to pinpoint the exact area where a fire has started or where the alarm has been raised.
The choice between the two systems often comes down to a question of cost but there is no doubt that on a large vessel, particularly on a passenger ship, the addressable systems are far more preferable.
In operation, both systems work in much the same way and will use common components. The difference between the two systems is the way in which the detectors and call points are connected to the control panel. In a conventional system, the detectors and call points are linked to the control panel using individual wire connections, whereas in an addressable system a number of detectors and call points will be linked together using what are referred to as loops. This means that in a conventional system, although there are more wires and consequently a more expensive connection operation, the system is not as accurate as the addressable system. Each device along the loop in the addressable system has its own unique identifiable address but in the conventional system this is not the case.
Over the years there have been several incidents involving leakage of hydrocarbon gases from tanker cargoes. Leaks into pump rooms and other machinery spaces present a risk of explosion while leaks into void spaces and ballast tanks present a danger to crew entering those spaces. Gas detectors are used to identify the presence of these gases allowing appropriate action to be taken.
As with much of the equipment on ships, the gas detection equipment is not unique to the marine industry and is identical to devices used in several shore-based applications. The devices can be obtained from several sources including direct from manufacturers, from ship chandlers and specialist safety equipment suppliers.
Gas detection equipment measures a gas’s concentration against a calibration gas that acts as a reference point. In the early days of gas detection, monitors detected a single gas, but a modern unit can detect several toxic or combustible gases, or even combinations of them.
Detection systems for ships come in three basic types: fixed, portable and personal.
Fixed gas detectors are set up in much the same way as a fire detection system with strategically-placed detectors linked to a central control panel. At least one leading manufacturer markets a combined fire and gas detection system.
Portable gas detectors consist of a device that can be carried to any location for testing its atmosphere. They will be used for a variety of purposes such as fire patrols and checking before entry into enclosed spaces is attempted.
Personal devices are intended to be worn by crew when carrying out their duties in areas likely to be affected by gas leaks.
All types of gas detector require regular testing and calibration. Because of their obvious importance to safety, it is advisable for testing to be carried out before each use. SOLAS II-2 regulation 4 requires tankers to be equipped with at least one portable instrument for measuring flammable vapour concentrations, together with a sufficient set of spares and a means for calibrating such instruments. Where the atmosphere in double-hull spaces cannot be reliably measured using flexible gas sampling hoses, the spaces must be fitted with permanent gas sampling lines configured with the design of the spaces taken into account.
In addition, the pump rooms of tankers carrying cargoes with a flashpoint of below 60°C are required to be fitted with a system for continuous monitoring of the concentration of hydrocarbon gases. Sampling points or detector heads must be located in suitable positions in order that potentially dangerous leakages are readily detected.
When the hydrocarbon gas concentration reaches a pre-set level – no higher than 10% of the lower flammable limit – a continuous audible and visual alarm signal must be automatically activated in the pump- room, engine control room, cargo control room and navigation bridge to alert personnel to the potential hazard.
Details of the equipment and performance standards for fixed gas detection systems were formulated some years after the FSS Code was first published and are contained in a new Chapter 16 that was added to the code in 2007. An updated version was approved in 2010 and can be found in MSC.1/Circ.1370.
In September 2013, the IMO amended SOLAS regulation XI-1/7 relating to the carriage requirements for portable instruments to test the atmosphere of enclosed spaces for oxygen, flammable products, H2S and CO.
There is something of an overlap with the requirement for portable instruments and the requirement for enclosed space entry drills and training every two months that became mandatory as of January 2015 under amendments to SOLAS (Regulation III/19). The IMO has urged flag states to accelerate the requirement for testing equipment and it may be that for some ships the need to carry equipment is already in place.
To accompany the new IMO regulation, there is an MSC circular on guidelines to facilitate the selection of portable atmosphere testing instruments for enclosed spaces. As well as a need to purchase suitable equipment, the regulation will also mean that most companies will need to amend their working practices and safety systems.
There is currently no requirement for a portable instrument on any ship type to be able to detect the potential gases that might be found in ballast tanks as a consequence of treating ballast water. Considering that some ballast systems – even explosion- proof versions – can produce highly flammable hydrogen or toxic chlorine, some concerns have been expressed as to what may happen if a fault develops in those systems.
An aspect of the type-approval for the explosion-proof ballast treatment systems is the requirement for alarms when hydrogen levels exceed certain levels and for the system to shut down if levels reach a point below the lower explosive limit, although the exact level can vary from system to system.
For systems where chlorine gas may be present, the main concern of the IMO is ensuring the gas is neutralised before or during discharge to protect the environment. However, for crew required to enter a ballast tank in a possible emergency, determining the level of either gas as well as those already covered may be a matter of life or death.Shipboard fire-fighting systems
Shipboard fire-fighting systems
Over time, new technologies have improved the arsenal of weapons that ship crews have in the battle against fire but fighting fire may well still involve manual means such as fire hoses and hand-held extinguishers, buckets and sand as well as advanced systems such as water mist, sprinklers and gas suppressants.
When it comes to fire extinguishers, the wrong choice can make matters worse. Part of a seafarer’s basic training will cover which type of extinguisher to use in different situations.
There are six different types of handheld extinguishers with each type intended for dealing with one or more of the different types of fires and completely unsuited for others:
- Powder fire extinguishers are ideal for use in mixed risk environments. They are the only effective solution for fires involving flammable gases.
- Foam fire extinguishers are ideal for use on fire involving solid combustible materials and are highly effective on flammable liquid fires. The layer of foam applied by these extinguishers helps to prevent re-ignition after the fire has been extinguished.
- CO2 fire extinguishers are suitable for use on flammable liquid fires and are extremely effective at extinguishing fire involving electrical equipment.
- Water fire extinguishers are suitable for use in environments containing solid combustible materials such as wood, paper and textiles. They should not be used around electrical equipment (unless water extinguishers with additive are used).
- Wet chemical fire extinguishers are usually supplied with a special application lance. They are intended for tackling large burning oil fires and are ideally suited to the kitchen/galley environment.
- Water mist works on the basis of using microscopic particles of water to cool a fire, suffocate it and then cool the burning media to prevent reignition. Water mists extinguishers are ideal for covering areas where multiple fire risks can be found.
Pumps and hoses
Manual fire-fighting when not involving fire extinguishers will rely on pumps and hoses. A sufficient supply of water for fighting fires is not normally a problem for ships unless the pumps and hoses are damaged or inoperable or if the vessel is at a berth where it either lays aground or where the water depth is very shallow. In the latter cases it is always a wise precaution for the ship’s officers and crew to ensure that a shore hydrant is available nearby.
Unlike fighting fires ashore where the volume of water used is not an issue, at sea an excess of water is highly dangerous and cause the ship to capsize. Water can also react with some cargoes releasing hazardous gasses or even causing further fires and explosions. The latest requirement for container ships to carry a water lance capable of penetrating a container may well help extinguish some fires, but some believe that it will be a matter of time before the use of such equipment will actually cause a fire to become much fiercer.
The FSS Code and SOLAS contain regulations that cover all aspects of the fire pumps, hydrants and hoses, including their capacity, placement and numbers. Exact details will be ship-specific and will also be dependent on ship type. The regulations also cover ventilation, dampers and fire doors.
A system will inevitably contain numerous valves to isolate parts of the system when maintenance or repair work is needed. The valves connecting the pumps to the sea chest should only be closed when work is being done so that at all other times there will be a ready supply of water to the system. Checking the status of valves is an essential part of regular inspections.
Piping is an often-neglected part of the fire system, but its condition is as important as any other part since a damaged or leaking pipe can render the whole system useless. Pipes for the fire system are generally of steel construction and therefore subject to corrosion. This is especially true of pipes on deck exposed to the open air and corrosion on these pipes often goes undetected, especially if paint is concealing areas of wastage.
A suitable fire hose should be stored close to each hydrant together with appropriate connectors and nozzles. As with the pipes, hoses should be checked regularly for damage. Visual checks will identify some damage but filling the hose and directing the spray overside on occasions will identify hidden leaks.
All ships are required to carry an international fire hose connector so that in the event of failure of its own firefighting system, a ship in port can have its piping and hosing system connected to a shore water supply. The connector can also be used to connect the system to the pumps of another vessel when in port or at sea.
Sprinklers and water mist
Most modern ships are now equipped with a sprinkler or water mist/fog extinguishing system. In such systems, the sprinkler head is usually a combined detector unit. Sprinkler systems can also be activated manually if a fire is seen before the system activates.
When heat or smoke activates the system, the head water is released to extinguish the fire. The types of systems are basically similar in that they use water released from overhead points when activated but the mist systems use less water and have other claimed advantages.
The water for the systems is supplied through the sea chest but there is also a tank of fresh water that is used in the first instance for priming the system so that the standing water in the pipes is not corrosive. Sprinkler and water mist systems can be brought into action faster than gas systems since it is not necessary to close openings, shut down ventilation or evacuate the space before release. The time needed to extinguish fires with water mist can be longer than for gas, but water mist also cools the space and controls smoke in the process. An unlimited water supply is also usually available.
In a water mist system, the water is under pressure and released through a spray head. The small water droplets allow the mist to control, suppress or extinguish fires by cooling both flame and atmosphere and displacing oxygen by evaporation. The mist is more penetrative than water from sprinklers and also acts as a smoke suppressant thus preventing other heads from being activated by smoke and so reducing water demand.
From a safety point of view, the ship’s stability is far less likely to be compromised by the free surface effect of the amount of water used and, for those systems using fresh water, carrying less of it means more cargo capacity is available or less fuel is needed. Water mist has been shown to be highly effective at extinguishing fires in both demonstrations and actual operational circumstances.
Water mist systems come in both high-pressure and low-pressure variants. Over the years, the pressure needed to produce the fine droplets has reduced from around 100bar to levels around 7bar in some systems. There are, however, still plenty of manufacturers that continue to produce high-pressure systems. Proponents of these argue that the higher pressure produces smaller droplets that aid in rapid extinguishing.
The water droplets can expand to almost 2,000 times in size as they vaporise, depriving the fire of essential oxygen. The more droplets there are and the greater the area they occupy, the more effective will be the suppression.
Although considered an improvement over sprinkler systems, water mist installations are not without problems. After several vessels were detained in US ports as a result of inoperable systems, a number of flag states and P&I clubs considered it necessary to offer advice on
maintenance and checking of systems. It appears that the majority of the detentions were due to systems being secured either by closed supply valves or by placing the system in a manual mode of operation.
When a system requiring an automatic operation capability is placed in manual mode, the sensors and alarms are not engaged and the system’s quick response capability is disabled. The chances of a fire spreading increase when the protected space is unmanned and the overall effectiveness of the water mist system could be reduced, particularly in terms of time needed to extinguish the fire.
Gas extinguishing systems
In addition to water, there are other means that are used to fight fire on ships. Some of the most effective systems, such as those that use Halon, have been banned under the Montreal Convention because of their ozone-depleting effects. An alternative called Novec 1230 is now used instead of Halon.
Novec 1230 systems are individually designed and appropriately sized storage cylinders chosen according to the hydraulics and quantity of agent required. The components are designed and tested to operate in the temperature range 0°C to 50°C. The cylinders are generally stored outside the area being protected although under certain circumstances they can be kept in the same space. Novec 1230 systems are designed to hold both the Novec 1230 in the form of a liquid and nitrogen, which is used to super-pressurise the container to 24.8bar at 20°C.
When the system is activated the contents flow into the distribution pipework to the discharge nozzle(s) where it is dispersed as a vapour in less than 10 seconds. During the discharge the enclosure will be fogged which may reduce visibility. This normally clears rapidly and should not obstruct the ability of personnel to safely exit the protected area.
Under normal conditions, Novec 1230 is a colourless and low-odour fluid with a density around 11 times that of air. It decomposes at temperatures above 500°C and it is therefore important to avoid applications involving hazards where continuously hot surfaces are involved. Upon exposure to flames, Novec 1230 will decompose to form halogen acids. Their presence will be readily detected by a sharp, pungent odour before maximum hazardous exposure levels are reached. Fire toxicity studies show that decomposition products from the fire itself, especially carbon monoxide, smoke, oxygen depletion and heat, may create a greater hazard.
The successful performance of a gaseous total flooding system is largely dependent on the integrity of the protected enclosure. It is essential that a room integrity test is performed on any protected enclosure to establish the total equivalent leakage area and enable a prediction to be made of the enclosure’s ability to retain Novec 1230.
The required retention time will depend on the particulars of the hazard, but MSC/Circ.848 states that this should not be less than 15 minutes. Longer retention times may sometimes be necessary if enclosures contain hazards that may readily become deep seated.CO2 fire extinguishing systems – protection and perils
CO2 fire extinguishing systems – protection and perils
Considering that Halon systems were banned because of their ozone depleting properties, it seems a little ironic that the more common replacement other than Novec 1230 is carbon dioxide (CO2) which is also highly criticised as a modern ‘pollutant’ and greenhouse gas.
CO2 can be used either in a hand-held extinguisher or as a flooding system. In a flooding system it is one of the most commonly used fire-extinguishing agents in ships’ engine rooms. It gas has excellent fire extinguishing capabilities and is relatively inexpensive but can pose a serious risk to personnel because it works by reducing the oxygen content in the atmosphere.
With CO2 systems, the period between detecting a fire and releasing the gas often seems quite long because crew must evacuate the area to avoid the lethal effects of the gas. As a consequence, minor fires have sometimes been allowed to escalate causing loss of life and even total loss of ships.
Issues with CO2 systems feature in many official accident investigations and advice to the industry is regularly promulgated by insurers, P&I clubs, class societies and other bodies. The concentration of CO2 above certain levels in fire-fighting applications is a major concern amongst fire safety regulators.
SOLAS does not prohibit the use of CO2 in systems protecting a ship’s engine room, or other spaces where crew has access during normal operation, but the risks to personnel are clearly recognised and SOLAS calls for various safeguards, such as two separate and interlocked controls, pre-discharge alarms and time-delays, to protect personnel in the engine room. SOLAS does not, however, allow portable CO2 extinguishers to be placed in the accommodation spaces on board ships, due to the associated risk to personnel.
For the typical engine room fire involving flammable liquids, it is important to introduce the required quantities of CO2 quickly to limit the escalation of the fire. Investigations reveal that evacuation, muster and head counts during engine room fires often take longer than expected because crew are not disciplined in mustering.
Because of limited storage capacity, very few ships can carry enough gas for more than a single discharge.
CO2 has a limited cooling effect and the temperature of equipment and structures in the engine room may be very high, in particular if the time taken to release the fixed fire-extinguishing system was long. There is a further risk to fire fighters or crew who enter the space too soon, thus allowing entry of oxygen-rich air, which can cause the fire to reignite. Most advice issued with regard to CO2 systems recommends fostering awareness of the hazards related to their use through detailed and unambiguous procedures, proper training and prescribed maintenance. The dangers of CO2 must be continuously stressed and training and experience transfer between crew should create a common understanding of the functionality, limitations and hazards associated with the ship’s specific installation.
The design of a CO2 system is covered in the FSS Code and will need to be approved by the flag state or the classification society but there are aspects which should be considered as common sense. For example, at least one engine room ventilation fan should be powered by an emergency generator so as to aid in making the engine room safe for entry after use of the system.
In addition, the dangers of a CO2 system are not confined to the spaces they are designed to protect but extend to the CO2 storage area itself. It is not unknown for the cylinders to leak, creating a suffocation hazard in the CO2 storeroom. As a consequence, there should be adequate ventilation and the area should be considered as an enclosed space with appropriate procedures in place for testing prior to entry.Fires on container ships
Fires on container ships
Containerisation has been responsible for a revolution in cargo handling and rapid port turnrounds but the use of containers also has safety implications. Often this is due to shippers deliberately declaring hazardous cargoes as something harmless to avoid paying premium freight rates. In such cases this may mean containers are stowed in inappropriate slots on board. There appears to be an increasing number of cases of hazardous cargoes catching fire or exploding and resulting in the loss of ships and lives.
There is an onus on shore staff when booking cargoes to be more vigilant and there is a requirement under IMDG for staff responsible for accepting hazardous cargoes to have undergone training to understand the requirements with regard to packing and separation of such cargoes. Well trained staff can often identify some cargoes as being hazardous even when the shipper is not aware of the particular hazard involved. For example, swimming pool cleaners can contain some highly-flammable components and the booking staff must be able to recognise proprietary names for some of the more hazardous types. However, dealing with the issue of deliberate concealment is difficult because inspecting cargoes inside containers is not easy to achieve.
Many recent cases of fire that have led to total loss of the ship have involved cargoes inside containers. An article published in 2018 by the Through Transport Club, suggested that container fires may occur on a weekly basis and statistics indicate there is a major container cargo fire at sea roughly every 60 days.
These have presented a particular problem for the industry as a whole and for crews on the ships affected because it is almost impossible to fight such fires using the equipment normally available on board. Some attempt at solving this has been made with the IMO’s new requirement (SOLAS regulations IMO MSC.1/ Circ. 1472) for some new container ships built from 2016 onwards to be equipped with lances able to pierce containers and fire monitors able to assist in directing water jets on to containers in high stacks. Ships with a breadth up to 30m should be provided with at least two mobile water monitors and ships with a breadth exceeding 30m should be provided with at least four mobile water monitors.
A lance is attached to the fire main by a hose and a battery-operated drill is usually used to pierce the container so that it can be inserted into the container. Most lance systems are designed to then be left inserted into the container and to operate continuously without the need for the crew to remain in the vicinity. Although this might extinguish some fires, it should not be forgotten that some chemicals react with water and if these are present in the container, a water lance may actually make matters worse.
However, both of these were available on the 2017-built, 15,262TEU Maersk Honam which suffered a major cargo fire in early March 2018 resulting in the death of four seafarers, but were ineffective in bringing the fire under control. Since then, there have been more container ship fires including two this year in the shape of Yantian Express and APL Vancouver. These are just the latest in a string of fires usually found to be connected to cargo being wrongly packed and wrongly declared.
To many, including classification societies and insurers, the current rules are inadequate and need to be revisited on a regular basis. Class societies are developing voluntary notations that go beyond the IMO requirements. For example, the ABS voluntary notation FOC which covers fire protection on container ships may require not four but 10 portable fire monitors, depending on the beam of the vessel.
ABS justifies this because when considering the sizes of the surface areas that need to be covered, the limited coverage that any one monitor may provide together with the possibility of restricted angles of attack limiting vertical reach and the possible interference due to lashing bridges, the number of monitors being carried would likely need to be split between the area forward and the area aft of the bay engaged in fire so having additional monitors available would be important.
The FOC notation also has requirements relating to the fire main and hydrants that go beyond SOLAS. ABS also has an FOC+ notation which addresses the concern that prolonged exposure to the excessive heat of a fire could weaken the hatch covers, leading to their possible failure and the collapse of deck cargo into the hold. To address this concern, the FOC+ notation identifies specific requirements for a fixed water spray hatch cover cooling system.
The International Union of Marine Insurance (IUMI) has called upon regulators, class and industry stakeholders to explore ways to improve fire detection and fire-fighting capabilities on container ships. One suggestion that has come from one of the IUMI’s own members suggests creating individual fire compartments below deck to prevent fire from spreading. These compartments would be fitted with fixed CO2 and waterbased firefighting systems. Boundary structures would also be fitted above deck to align with the water-cooled bulkheads below and also be fitted with fixed firefighting systems.
While these are all sensible suggestions, unless shipowners adopt them voluntarily or are forced to action by more stringent regulation, the likelihood of the issue of container ship fires being resolved any time soon is very small.
Following a number of container fires on its ships, notably the Maersk Honam in March 2018, Maersk line is considering ways to identify combinations of cargoes, shippers and freight forwarders likely to be connected to containers in areas where fires have started on board ships. If this can be achieved, then spot checks on containers will be made in future in an attempt to determine if cargoes are being deliberately mis-declared.
The spate of containership fires has continued in 2019. With just two months of the year having passed, Hapag Lloyd’s Yantian Express and APL’s APL Vancouver both suffered major fires and needed to be salvaged. In both cases, the seat of the fire was in the cargo holds although exact causes have still to be determined.
In recent years the IMO has laid down new rules for fire extinguishing systems on container ships but there is a widely-held belief that the size of modern container vessels – especially the ultra large ships – makes an effective fire-fighting system impossible to produce.
Another issue with containers is the mis-declaration of weights which has resulted in stowage and stability problems. It is a matter that ship operators have complained about for many years and the IMO has finally taken action and adopted amendments to SOLAS Chapter VI Regulation 2. These have been published as MSC.1/Circ. 1475.
Since 1st July 2016, all packed containers are required to have a verified gross weight (VGW) declared by shippers. This the certified gross cargo weight (including weight of all packing material) plus container tare weight. The measure has not proved popular with shippers, but under the rules containers cannot be loaded onto a vessel unless a certified VGW is provided