Fire Safety
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.
Some
precautions can be taken if cargoes are known to have a particular issue
connected with them such as spontaneous combustion in coal or iron ore cargoes
or the need to be inerted to prevent volatile fumes from oil and gas cargoes
escaping in tankers.
Many
recent cases of fire that have led to total loss of the ship have involved
cargoes inside containers. An article published last year 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 water-based firefighting systems.
Boundary
structures would also be fitted above deck to align with the water-cooled bulkheads
below and also be fitted with fixed fire-fighting systems.
While
these are all sensible suggestions, unless ship owners 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.
Fire and gas detection basics
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 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 has its own unique identifiable address
but in the conventional system this is not the case.
Sniffing out silent killers
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 neutralized 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
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 re-ignition. Water mists extinguishers are ideal for covering areas where multiple fire risks can be found.
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. 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
100 bar to levels around 7 bar 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 protection
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 appropriate 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 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 store room. 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.
