Oil Tankers: Fire Safety by Design

Oil Tankers:
Fire Safety by Design

by P. Galbraith, BA, AIFireE - Training Department, Merseyside Fire Brigade

1. Introduction

The aim of this paper is to give a greater understanding of fire safety design in oil tankers and their firefighting systems. Three aspects have been considered I will show:

The design features that have been built into the ship to reduce the risk of fire, or to help contain a fire.
The fire fighting systems on board ship.
The actions taken by the crew in the event of a fire.

Many of these features will be found on other types of ship. The ship used as an example is the 'SUEZMAX' class of oil tanker. BP Shipping has taken delivery of three of these ships, the Harrier, Hunter and Hawk, from Samsung Heavy Industries, Korea. The Suezmax class is a mid-size oil tanker, with a slow speed diesel engine as the main propulsion unit. It is capable of carrying crude or fuel oil. The Suezmax has the following design specifications:

Tonnage:	137,000 Ton (dead weight)
Length:	274.1m
Breadth:	46m
Draught:	15.85m
Engine:	Samsung B&W 6S70MC, producing 20,700 BHP @ 91rpm
Speed:	14.5 knots @ 90%
Boiler:	2 x Mitsubishi Mac 35B, producing 35 Tons/hr
Crew:	33

2. Fire Prevention and Isolation Design

This ship has been designed to meet the 'safety of life at sea' regulations 1974 (SOLAS) with protocol of 1978 and amendments of 1988/92. It will also meet the Maritime regulations of Bermuda.
The ship has been designed to reduce the risk of fire, or to contain a fire. It has been isolated into Hazardous and Non-Hazardous areas. Effective means have been taken throughout the ship to detect combustible gases, prevent ignition sources and give warning of possible fire.

2.1. Bulkheads

The cargo deck, cofferdams, paint store, chemical store and machinery compartments are classed as hazardous areas. These areas are isolated from the accommodation by A-60 bulkheads. An A-60 bulkhead or deck is constructed of 4.5 mm thick steel, suitably stiffened. The steel is then insulated with 50 mm of glass wool. This type of bulkhead or deck will provide a minimum of 60 minutes protection from smoke or flames.
There is an A-60 deck between the accommodation and the machinery compartments, and the accommodation and the bridge. The A-60 bulkhead runs across the front of the accommodation and 3m down the port and starboard sides. This ensures that the accommodation will not be affected by fire from either the machinery compartments or the cargo deck. The bridge is also protected from an accommodation fire.
The accommodation is classed as a non-hazardous area. The corridors are made from B-0 class panels. These are 1.6 mm thick steel panels with 50 mm of mineral wool to provide insulation. They will provide 30 minutes protection from smoke or flames. Draught stops are fitted in the corridors (less than 14m apart). These stops are fitted from the ceiling panels up to the deckhead and will help prevent smoke from travelling along the corridors.
The cabin walls are made from C class panels which are sandwich panels of galvanised steel coated with a PVC film. They have 50 mm of rock wool insulation. These panels will provide 30 minutes protection from smoke and heat (see Figure 1).
The accommodation, engine room, emergency exit, lift shaft and stairwells are surrounded by A-60 bulkheads to ensure an adequate escape route is provided.

2.2. Fire doors

Doorways between A-60 bulkheads are A class doors, fitted with a self-closing device. Doorways in the accommodation corridor are fitted with B class doors, and magnetic self closing devices, linked to the fire alarm panel. Cabin doors are B class doors.

2.3. Fire loading

Accommodation fittings require Lloyds Fire Certification. This ensures that the accommodation fire loading is kept to a minimum.

2.4. Electrical equipment

In hazardous areas such as the cargo deck, where there is a possible danger of combustible gases, the electrical equipment must be certified as suitable for use in this area to prevent the ignition of explosive gas or air mixtures, should they exist.

2.5. Emergency isolation

Emergency isolation is available in the Foam Generator and Fire Control Centre (FGFC). This is situated on the upper deck, starboard side. The following isolation controls are in this room:

Cargo pump stop.
Control for the engine room fire dampers, showing whether open or closed.
Control for ventilation fans for the fuel oil, lubricating oil, engine room, cargo room, inert gas room, steering gear room and accommodation.
Emergency start/stop for the fire pumps.
Emergency trips for the engine room fuel oil and lubricating oil tanks above 250L.

3. Inert Gas System

Soon after the advent of very large crude carriers (VLCC's), a series of serious explosions occurred during tank cleaning operations on ships sailing in ballast. After these accidents, detailed investigations were carried out involving the International Maritime Organisation (IMO) and several oil companies. The exact cause was not defined, but was thought almost certainly due to static electricity.
Inert gas systems were developed to reduce the oxygen content in the cargo tanks. Hydrocarbon gas will not normally burn in an atmosphere less than 11% of oxygen by vol. Therefore, to prevent an explosion or fire in the cargo tanks, the vapour space oxygen content is kept below 8% by using inert gas from the boilers or an inert gas generator. Boiler flue gasses have the following composition:-

oxygen	4%-5%
CO2	12%-14%
oxides of nitrogen	0.2%-0.4%
nitrogen	remainder
temperature	400^oC

The schematic diagram (Fig 2) shows the layout of the inert gas system on this ship. Flue gas from the boiler uptakes is passed through a scrubber. This cools the gases and removes the sulphur particles. It is then passed through fan blowers and piped to the cargo tanks under slight pressure, (300-1,000 mm W.G.). The system is capable of producing 13,900 m³/hr of inert gas. There is also a diesel inert gas generator and a shore connection for use if the boilers are shut down.
The normal cycle of operation, starting from clean empty tanks is to blow inert gas through all the tanks until the oxygen content has been reduced to the lowest possible level, venting the tank contents to atmosphere.
When cargo is loaded the inert gas is shut down and the tanks vented. Once loaded a positive pressure is maintained in the ullage space to prevent the ingress of air. Whilst discharging the inert gas keeps pace with the falling level of liquid.
The inert gas system can also be used to ventilate the tanks when entering dry dock. As an emergency measure the pump room can be inerted, eg. in the event of a serious oil leak from the pump.
To prevent hydrocarbon gases returning to the uptakes, non return valves and a water seal are placed in the system. The system is continuously monitored in the Cargo and Engine Control Room, with a repeater on the bridge. Alarms will sound on:

High O2 content (above 5%)
Low water seal levels
Low/high pressure (200/1260 mm H.G.)

The cargo pumps will trip if the pressure falls below 100 mm W.G.

4. Automatic Detection and Alarm Systems

Automatic detection and alarm systems are used to alert personnel to a possible fire situation or give early warning.

4.1 Gas detection system

Gas detectors sample the air for the presence of flammable gas. On this ship, infra-red detectors are used; catalytic filament detectors can also be used. Each sensor has its own flame trap. The sniffer lines in the double bottom tanks have a ball valve to stop the lines flooding if full of sea water. The detectors are located at low and high elevations to detect gases which are heavier and lighter than air.
There are two separate detection systems on this ship:

Pump room: This system gives an alarm when two sensors show a 10% mixture. At 30% the system will trip the cargo pumps, assuming there is a leak from the pump or pipe work.
This system detects the gases in the ballast tank, fore peak, paint store, engine room, cofferdams and accommodation ventilation intakes.

The alarm panel is located in the FGFC room and the Cargo and Engine Control Room (CECR). An alarm will also sound if the sniffer pipe becomes blocked or there is a low sample flow.

4.2 Fire alarm system

The fire alarm system on this ship is the addressable type of system. It comprises smoke, heat and ultra-violet light detectors.
Smoke detectors are designed to sense smoke produced by combustion. Ionization detectors are used since they provide a faster response time to high energy fires that produce large numbers of the smaller smoke particles. There are 96 detectors in the accommodation and deck areas; one in each cabin, public room and the corridors; 44 detectors are located throughout the engine room.
Heat detectors are best suited for fire detection in confined spaces subject to rapid and high heat generation, directly over hazards where hot flaming fires are expected. These detectors are located in the galley, the incinerator room and seven in the engine room.
Ultra-violet detectors respond to the ultra-violet light generated by the flames of a fire. Due to their fast detection capabilities, these detectors are used in high hazard areas. There are five of these detectors in the engine room, located so that they have a clear field of vision of the area they cover.
Break glass alarm points are located throughout the ship: 17 in the accommodation and deck, 14 in the engine room.
The system is split into four loops; two in the engine room and two in the accommodation. The master panel is in the FGFC room, with repeaters in the bridge and the CECR room. When the fire alarm is activated a second generator automatically comes onto load, to accommodate the extra electricity demand, ie, fire pump, etc.

5. Fire Fighting Systems

There are a number of fire fighting systems used on this ship, ranging from portable fire extinguishers for small fires to fixed fire fighting systems.

5.1 Portable and wheeled fire extinguishers

Portable and wheeled fire extinguishers are provided throughout the ship in the following quantities:

Type	Location
	E/R	Acc/Deck
9L foam	22	2
45L foam	1	-
135L foam (fixed)	1	-
20L foam applicator	-	10
6kg Dry powder	1	21
45kg Dry powder	-	2
6.8 kg CO2	4	4
18 kg CO2	-	1

5.2 Fire water mains and pumps

The schematic diagram (Fig. 3) shows the fire main and pumps on this ship. It comprises of:

two fire pumps producing 200m³/hr at 12bar.
fire and deluge pump producing 250m³/hr at 12bar.
emergency pump producing 72m³/hr at 8bar.

The following planned water consumption has been used to size the pumps.

deluge system	244 m³/hr
largest foam monitor	338 m³/hr
two hydrants	50 m³/hr
accommodation spray	36 m³/hr

assuming the maximum load is =

foam		two		accommodation
monitor	+	hydrants	+	spray	=	Total
338		50		36		424 m³/hr

or in the case of evacuation.

Deluge		two		accommodation
system	+	hydrants	+	spray	=	Total
244		50		36		330 m³/hr

The pumps are electric centrifugal self-priming pumps. The main fire pumps draw sea-water from a separate sea chest than the emergency pump. All the fire pumps can be started from the following places:

Bridge
Cargo and Engine Control room
Fire Control Centre
Pump side

The fire main feeds ten hydrants in the engine room, two per deck. At the accommodation the main branches feed the port and starboard sides. There are two valves per deck, located at the entrances to the accommodation. The fire main also runs down the cargo deck, feeding hydrants on the port and starboard sides (total 14). There are hose reels (40mm x 18m) placed throughout the ship; two per deck in the engine room; one per deck in the accommodation and seven on the cargo deck.
The International shore connection can be found on the upper deck, port and starboard sides.
A water curtain is provided, running across the front of the bridge and the port and starboard sides. This provides protection against a cargo deck fire. A sprinkler system is also provided for the chemical stores in the engine room and second deck, and the paint stores in the engine room and fore peak. All these sprinkler systems are manually operated.

5.3 Deluge system

This is a new system developed by BP Shipping, in response to the MV British Trent accident. This ship was involved in a collision in fog. In the collision the fire main was severed. On evacuating the ship, one life boat was covered in burning oil, with the loss of ten lives.
The deluge system is designed to give a continuous water curtain around the life boat stations, enabling the boat to be lowered in safety. Spray nozzles are fed from the fire main and provide a water curtain that protects the lifeboat from above, forward and the side. The deluge system is operated manually from the FGFC room on the order to evacuate. Because of the large demand of this system an extra pump has been installed.

5.4 Foam fire fighting system

The foam system on this ship is used for fighting a fire on the cargo deck. Fig. 4 shows the schematic diagram and operating instructions for the system. The system comprises:

Foam bulk storage tank
Foam pump
Variable flow injector (proportioner)

The foam system is operated from the FGFC room. The foam bulk storage tank contains 4m3 of fluoro-protein foam, with an additional 100L tank used for exercises. The foam is pumped from the tank by an electrically driven pump. The foam concentrate is admitted to the foam main via the variable flow injector, where it mixes with sea water at 3%, fed from the fire pumps.
The foam main feeds seven monitors on the cargo deck and seven foam valves, for use with portable foam making equipment. The foam mixture is aerated at the monitors with an expansion rate 12:1. This produces low expansion foam, which is laid across the cargo deck. Low expansion foam is used to give a good throw and make the foam resistant to wind drift.
The fixed monitors have the following specifications:

Manual operation
Inlet pressure:	6 bar
Max capacity:	5,500 L/min
Operating capacity	1,250 L/min
Throw	60m
Rotation	360^o
Elevation	-45^o to 85^o
Locking position	every 8^o
Operating time	20 minutes

The foam monitors can also be used as water jets. In addition to the fixed foam system, there are four foam boxes on the cargo deck containing separate foam branch pipes and 10 x 20L drums of foam concentrate.

5.5 CO2 Fire extinguishing system

On this ship carbon dioxide is used as a smothering agent in:

Engine room
Pump room
Inert gas fan room
Emergency generator room
Incinerator room

Fig. 5 shows the CO2 system and its operating instructions for the engine room and pump room. The system can be used to flood both rooms together or separately. The CO2 system can be operated remotely in the FGFC room or manually in the CO2 room.
When the CO2 control box is opened, alarms are actuated in the engine room and pump room to warn the crew that the CO2 is about to be released. The air conditioning fans will automatically stop and the vents will close for that area of the ship. A head count should be taken before discharging the system.
When CO2 is discharged frozen particles (dry ice) may form in the gas stream. These particles may become electrostatically charged. Therefore, the system should not be discharged into a compartment when flammable vapours have not been ignited. The system will discharge in two minutes. The system can be used once in the engine room and up to three times in the pump room.
Once actuated the compartment should remain isolated, with a watch kept on surrounding bulkheads and decks, until the compartment has cooled.
In addition to the main CO2 system there are separate systems for the inert gas fan room, emergency generator room and the incinerator room. These systems comprise of four CO2 gas cylinders manually operated.
CO2 is an asphyxiant and cannot be detected by sight or smell. No one should enter a compartment after operation without suitable breathing apparatus. The compartment should be fully ventilated after discharge. Emergency B.A. sets (10 mins) are provided in the engine room and pump room.

5.6 Steam smothering system

Steam is an inefficient form of smothering. Large quantities are required and there is a substantial delay before rendering the atmosphere incapable of supporting combustion. Due to the possibility of static electricity generation, steam should not be injected into a compartment containing an un-ignited flammable atmosphere.
On this ship steam is used as a smothering agent in the scavenge air receiver, on the main engine. Quantities of oil can build up in the receiver. If ignited by the hot gases from blowpast of the piston rings, low pressure steam (6bar) is injected into the receiver. Steam is used to reduce thermal shock to the piston and linings of the main engine.

6. Emergency Procedures

Each ship has its own contingency plans that are adopted in an emergency. This can range from a fire, to a burst discharge pipe, a collision between ships or a man overboard.

6.1 Training

BP Shipping sends its ship's officers on a four day firefighting course once every five years. Lectures and exercises are used to train the Philippine crew members. The senior ships officers attend a management and control course, which gives them the skills to manage a major incident. Drills are carried out once a week.

6.2 Emergency organisation

In the event of an emergency, such as a fire, the master is in overall charge. The following actions take place:

The alarm is raised
The incident is located and assessed
The manpower and equipment required to deal with the incident is organised.

The ships' crew is allocated to teams on joining the ship. One team assembles at the FGFC room. A second team assembles at the Fire Control point on 'C' deck. There is a third fire control point on the steering flat. These control points contain the following:

There is a B.A. compressor in the FGFC room.
The incident is assessed and a report made to the Fire Control Centre.
Action should be taken to contain the fire and extinguish it. In all cases of fire, speed of attack and in raising the alarm are essential. Any cargo or ballast operations should be stopped immediately and then all valves closed. All doors, openings and tank apertures should be closed as soon as possible and mechanical ventilation should be stopped. If at sea the tanker should be manoeuvered so as to enable the fire to be restricted and attacked from windward.
Before arrival at a terminal to load or discharge cargo, the ship's fire main should be charged and fire hose connected, one forward and one aft of the ships manifold. Monitors should be ready for use and portable extinguishers should be conveniently placed near the ships manifold.
If at a terminal, the ships personnel should take the same actions and notify the terminal personnel. The following information should be passed onto the local fire brigade:

Name of tanker
Location
Nature of fire
Nature of immediate assistance required
Nature of casualties, if any.

The ship's engines should be brought onto stand-by. When the local fire brigade attends the incident, the ship's fire plans will be found at the head of the gangway (port and starboard). These will show clearly for each deck, the location and particulars of the fire fighting equipment.

7. Conclusion

In order to understand how an oil tanker fire can be contained and extinguished, it is necessary to have a good knowledge of ship design and the fire fighting systems. The Suezmax class of oil tanker has been used as an example to show:

How a ship is designed to contain a fire and to prevent its spread.
The firefighting systems that are available to extinguish a fire.
The procedures that the ships personnel would take in a fire situation.

8. Acknowledgement

The following are gratefully acknowledged for providing the information used in this paper: Mr K Miller, BP Shipping and Samsung Heavy Industries.

The above is an article that appeared in the IFE Journal (January 1999)