Carbon Dioxide (CO2) Extinguishing Systems

Carbon dioxide (C02) extinguishing systems have, for a long time, been approved for ship installation as well as for industrial occupancies ashore. Aboard ship, carbon dioxide has been approved for cargo and tank compartments, spaces containing internal combustion or gas-turbine main propulsion machinery and other spaces.

Properties of Carbon Dioxide

Carbon dioxide is normally a gas, but it may be liquefied or solidified under pressure. At -43°C (-110°F), carbon dioxide exists as a solid, called "dry ice." The critical temperature of carbon dioxide is 31°C (87.8°F). Above that temperature, it is always a gas, regardless of pressure. Carbon dioxide does not support combustion in ordinary materials. However, there are some exceptions, as when C02 reacts with magnesium and other metals. Carbon dioxide is about 1.5 times heavier than air. This adds to its suitability as an extinguishing agent, because CO2 tends to fall through air and blanket a fire. Its weight makes it less prone to dissipate quickly. In addition, carbon dioxide is not an electrical conductor; it is approved for extinguishing fires in energized electrical equipment.

Extinguishing Properties of Carbon Dioxide

Carbon dioxide extinguishes fire mainly by smothering. It dilutes the air surrounding the fire until the oxygen content is too low to support combustion. For this reason it is effective on class B fires, where the main consideration is to keep the flammable vapors separated from oxygen in the air. C02 has a very limited cooling effect. It can be used on class A fires in confined spaces, where the atmosphere may be diluted sufficiently to stop combustion. However, C02 extinguishment takes time. The concentration of carbon dioxide must be maintained until all the fire is out. Constraint and patience are needed.

Carbon dioxide is sometimes used to protect areas containing valuable articles. Unlike water and some other agents, carbon dioxide dissipates without leaving a residue. As mentioned above, it does not conduct electricity and can be used on live electrical equipment. However, fire parties must maintain a reasonable distance when using a portable C02 extinguisher or hoseline from a semiportable system on high voltage gear.

Uses of Carbon Dioxide

Carbon dioxide is used primarily for class Band C fires. It may also be used to knock down a class A fire. It is particularly effective on fires involving flammable oils and greases.

Electrical and electronic equipment, such as motors, generators and navigational devices.

Hazardous and semihazardous solid materials, such as some plastics, except those that contain their own oxygen (like nitrocellulose) machinery spaces, engine rooms and paint and tool lockers.

Cargo spaces where total flooding with carbon dioxide may be accomplished.

Galleys and other cooking areas.

Compartments containing high value cargo, such as works of art, delicate machinery and other material that would be ruined or damaged by water or water-based extinguishing agents.

Spaces where after-fire cleanup would be a problem.

Limitations on the Use of Carbon Dioxide

Effectiveness. C02 is not effective on substances that contain their own oxygen (oxidizing agents). It is not effective on combustible metals such as sodium, potassium, magnesium and zirconium. In fact, when C02 is used on burning magnesium, it reacts with the magnesium to form carbon, oxygen and magnesium oxide. The fire is intensified by the addition of oxygen and carbon, a fuel.

Outside Use

To be fully effective, the gas must be confined. For this reason, C02 is not as effective outside as it is in a confined space. This does not mean that it cannot be used outside. Portable CO2 extinguishers and hoselines have extinguished many fires in the open. An outside fire should be attacked from the windward side; the CO2 should be directed low with a sweeping motion for a spill fire, or down at the center of a confined fire. The effective range for a portable C02 fire extinguisher is about 1.5 m (5 ft).

Possibility of Reignition

Compared with water carbon dioxide has a very limited cooling capacity. It may not cool the fuel below its ignition temperature, and it is more likely than other extinguishing agents to allow reflash. (Its main extinguishing action, as noted above, is oxygen dilution.) When portable C02 extinguishers or hose lines from semiportable extinguishers are used, additional backup water hoselines should be brought to the scene. In case of live electrical equipment, an additional nonconducting agent must be brought to the scene.

When a space is flooded with CO2 the concentration must be kept up to a certain level After the initial application of a set number of C02 cylinders, additional cylinders must be discharged into the space periodically. These backup applications maintain the concentration of C02 for periods varying from hours to days. C02 works well in confined spaces, but it works slowly; patience is the watchword.

If a flooded space is opened before the fire is completely extinguished, air entering the space may cause reignition. Carbon dioxide cannot be purchased at sea. Reignition requires a second attack, at a time when less C02 is available.

Hazards. Although carbon dioxide is not poisonous to the human system, it is suffocating in the concentration necessary for extinguishment. A person exposed to this concentration would suffer dizziness and unconsciousness. Unless removed quickly to fresh air, the victim could die.

Carbon Dioxide Systems

Carbon dioxide extinguishing systems aboard vessels are usually not automatic. However automatic systems may be installed in certain ships and towing vessels with Coast Guard approvaL In the manual system, a fire detector senses fire and actuates an alarm. The engine room is alerted, and the bridge and CO2 room are notified as to the location of the fire (see Chapter 6). After it is verified that a fire actually exists, the amount of carbon dioxide required for the involved space is released from the C02 room.

Coast Guard regulations require that an evacuation alarm be sounded when CO2 is introduced into a space that is normally accessible to persons on board, other than paint and lamp lockers and similar small spaces. However on systems installed since July 1, 1957, an alarm is required only if delayed discharge is used. Delayed discharge is required where large amounts of C02 are released into large spaces. Delayed discharge may also be required for smaller spaces from which there are no horizontal escape routes.

The alarm sounds during a 20-second delay period prior to the discharge of carbon dioxide into the space. It uses no source of power other than the carbon dioxide itself. Every carbon dioxide alarm must be conspicuously identified with the warning "WHEN THE ALARM SOUNDS VACATE AT ONCE. CARBON DIOXIDE IS BEING RELEASED."

Portable and semiportable C02 extinguishers may be located in certain spaces. Small systems, consisting of one to four C02 cylinders, a hose and a nozzle, are often provided to protect against specific hazards. Those who work in the areas protected by these appliances should be familiar with their operation.

PYROMETERS

A pyrometer is an instrument for measuring temperatures too great for an ordinary thermometer. It is used to find the temperature of a fire. An important use of pyrometers is in checking the progress of a fire that cannot be seen, such as a fire that has been confined in a closed compartment or hold.

By taking readings at the same location at various times, one can tell if the fire is gaining or lessening in intensity. By moving the pyrometer to different locations along a bulkhead or deck, you can determine if the fire is extending laterally.

Pyrometers are attached to, or embedded in either of two types of bases. The usual type base may be placed on the deck over the fire space. The magnetic type can be "slapped" onto the outside of a bulkhead of a burning space. A chain should be attached to the base of the pyrometer. It can be used to pull the instrument across a deck that is too hot for personnel. It is also useful in lowering the pyrometer into a hot area.

A pyrometer can be useful in evaluating the success or lack of success when flooding a burning compartment with carbon dioxide. You should keep in mind that great patience is needed to successfully extinguish cargo hold fires with carbon dioxide. One cannot "take a peek" to see how things are going. Opening up would significantly dilute the extinguishing gas within the cargo compartment, which would destroying its effectiveness. Using a pyrometer and checking the variations in temperature should give you your information. A rising temperature after carbon dioxide has been introduced would indicate two possibilities:

1) the amount of carbon dioxide introduced is insufficient and more is required, or

2) the carbon dioxide is not reaching the fire (directed to the wrong fire zone, a control valve is closed or malfunction of the system). A steady lowering of the temperature would indicate that the carbon dioxide has either extinguished the fire or has it under control. However, though a steady lowering of the temperature is observed or even if the temperature reading is down to 66°C (150°F) or less, these encouraging readings should not be interpreted as a signal to open the compartment. There should be no need to open a cargo hatch until port is reached. After all, the damage to the cargo has already been done by the fire.

Fire Aboard The SS African Star

On the morning of March 16, 1968, at about 0340, the dry-cargo vessel SS African Star col­lided in a meeting situation with the tank barge Intercity no. 11 in the lower Mississippi River, in the vicinity of mile 46 Above Head of Passes (AHP). The African Star's bow penetrated the Intercity no. 11 on the after port side, at an angle of 45°. The motor towing vessel Midwest Cities was pushing two tank barges, Intercity no. 11 and Intercity no. 14 (the forward barge). The two tank barges were identical. A few minutes before the collision, the African Star was making about 16 knots on a 140° true course, the Midwest Cities was making 6 knots on a 320° true course with a relative closing speed of 22 knots. Visibility was good and each vessel had been advised of the other vessel's movements on its own radio frequency. Because of the lack of a common radiotelephone frequency, direct communication between the vessels was not possible.

Both vessels were equipped with marine radar units. Both units were in operation prior to and at the time of the casualty, but neither unit was being continuously observed by watch personnel. The pilot of each vessel sighted the navigation lights of the other vessel 1 1/2 miles, and later sighted the other vessel on radar. Witnesses in passing vessels reported that they could easily see the navigation lights on the Mid­west Cities, Intercity no. 14 and African Star. The movements of the vessels were not materially affected by wind or current. The steering gear and machinery of both vessels were in good op­erating order. The African Star had a licensed pilot, but the Midwest Cities had an unlicensed pilot, however, both pilots had extensive experience on the Mis­sissippi River. There was a lookout on the bow of the African Star, but none on the Midwest Cities. The master, third mate and helmsman were also on the bridge of the African Star.

The Collision
Different versions of the maneuvers were given by personnel on each of the two vessels.
Midwest Cities Version - The Midwest Cities was running parallel to the side of the river, about 250 feet from the east bank. The pilot considered it to be a head-and-head meeting situation, and the pilot sounded the appropriate one-blast whistle signal for a port-to-port passing. The African Star responded with one blast. He assumed a safe passage until the African Star sounded two blast when her bow was abeam the lead barge. He saw the African Star's green side­light and responded with one blast. He then blew four blasts on the whistle, backed full astern from full ahead and put the rudder hard right. How­ever, it was too late to avert a collision between the African Star and barge Intercity no. 11.

African Star Version - The pilot of the African Star stated that his vessel was slightly west of mid ­river when he sighted the Midwest Cities two white tow lights and green sidelights on his star­board bow. The tow appeared to be favoring the west bank and running parallel to it. It appeared to him to be a normal starboard-to-starboard meeting situation, not a head-and-head meeting. When the Midwest Cities tow was 1/2 to 3/4 mile ahead, he sounded two short blasts on the whistle, but no reply was heard. As the pilot headed for the radar, the third mate called his attention to the tow crossing his starboard bow showing red sidelights. This was about 2 minutes after the two-blast signal was sounded. Hard right rudder, one blast and then emergency full astern were ordered and executed. By this time, the situation was beyond the point of corrective action a col­lision was unavoidable. Full astern was in effect a minute before the collision.

In his analysis of the incident, the commandant of the U.S. Coast Guard concluded that the wit­nesses gave such conflicting testimony that it was impossible to reconstruct the events leading up to the collision.

The Fire
Intercity no. 11 was loaded to a draft of about 9 feet 6 inches, corresponding to approximately 19,000 barrels of crude oil. An analysis of the Louisiana "sweet" crude it carried revealed a 30.6° API a flash point (Pensky Martens) of 80.0°F, and a Reid vapor pressure of 3.2 psia, which categorized the product as a grade C flam­mable liquid. When the collision occurred, the general alarm was sounded on the order of the master of the African Star. At this time, the oncoming watch personnel were in varying degrees of readiness and, except for those on watch, all crew members and passengers were asleep or resting in their quarters.

In less than a minute, fire broke out and sev­eral explosions occurred. The most likely source of ignition was high heat due to metal-to-metal friction or sparks, produced when the barge was sheared by the bow of the African Star. Another possible source of ignition was sparks generated by the severing of the electrical cable leading to the navigation lights on Intercity no. 14. When fire broke out on the barge and in the surrounding water, the pilot of the Midwest Cities backed full to break the port wire and to clear the intense fire. He estimated it took about a min­ute to get free; his vessel was backing toward the west bank. Intercity no. 11 grounded and sank near the west bank at mile 45.7 (AHP). The Mid­west Cities was downwind of the point of collision and escaped with only minor damage.

The southeasterly wind carried flammable vapors over the African Star from bow to stem (because of the vessel's position relative to the wind direction). The flammable vapors ignited, engulfing the vessel in flames. The pilot backed clear and intentionally grounded the vessel on the west bank at mile 45.8 (AHP). The tarpaulins had been ignited, and there were fires in holds 2, 4 and 5. Containers and other deck cargo were burning, as was the paint on the ship. Dense smoke filled the engine room and accommoda­tion spaces.

Firefighting and Rescue
Problems were encountered in lowering the life­boat and launching the inflatable life raft; the boat cover and man ropes had burned, and the plastic cover of the life raft had ignited. The in­tense fire, heat and smoke in the quarters gutted the passageways, and a number of passengers and crew members were trapped. Several people tried to escape through portholes when they found that the passageways outside their quarters were im­passable. Others were burned when their life preservers and clothing ignited. For a while the fire and heat on the port side were too intense to endure. There was some minor confusion during the first few minutes after the alarm was sounded. However, this was quickly dispelled under the leadership of the master and his officers. After the African Star was grounded, the master went to the cabin deck to see to the safety of the passengers and crew.

During this time, he became seriously burned about the feet, face and hands. As a result, he was immobilized and had to be carried back to the bridge by the crew. At first, burning oil on the water surrounding the vessel prevented personnel from jumping overboard to get away from the burning vessel. The second mate gathered a number of passen­gers and crew into a small room on the African Star for refuge until the fire subsided. He then supervised the extinguishment of small fires in and around no. 1 lifeboat. By this time, the cur­rent and the movement of the African Star had separated the vessel from the oil burning on the water, the lifeboat was lowered to the edge of the deck and the injured crew members and pas­sengers were assisted into the boat and lowered to the water's edge.

Other crewmen and passen­gers were able to climb or jump into the water and swim ashore. The second mate observed large fires burning aft on the main deck. He organized a firefighting team that advanced hoselines to the area. They were successful in confining the deck fires and cooling the flammable-liquid cargo. An oiler in the engine room was forced to leave because of difficulty breathing in the smoke. How­ever, the chief engineer, third assistant engineer, and fireman / watertender continued to maintain the engine room plant in full operation. Power was maintained to keep the vessel aground, the lights on and the fire and bilge pumps in opera­tion.

Rescue operations had commenced fol­lowing the Midwest Cities request for immediate assistance via the marine operator in New Or­leans. Badly burned victims were quickly evacu­ated by U.S. Coast Guard helicopters. This operation is credited with saving the lives of a number of people injured on the African Star. The Midwest Cities, a New Orleans fireboat and a local ferry with fire apparatus on board assisted Coast Guard boats in fighting the fire. Firefighting was complicated by inaccessibility to the cargo manifest of hazardous materials lo­cated in the chief mate's room. In addition, a number of deck fire hoses had been burned. The combustibles on deck and in the holds continued to burn after the vapor and oil spray fires had subsided.

Firefighting by the African Star crew controlled the fire until the U.S. Coast Guard vessels and other help arrived. The fire in hold no. 5 was con­tained by use of the ship's C02 extinguishing system. At about 0530, the fires on board the African Star had been brought under control, and the Midwest Cities departed to retrieve Intercity no. 14, adrift in the river. Intercity no. 14 was un­damaged. The many fatalities and injuries sustained on board the African Star were due to the rapid spread of fire, the heat and smoke in living spaces and the burning oil on the water surrounding the vessel, which kept most personnel from imme­diately jumping overboard. A total of 11 passager and 52 crewmen on the freighter, 2 pas­sengers were killed and 9 were injured, 15 crew members were killed, 4 were missing and pre­sumed dead, 31 were injured, and 2 escaped in­jury. Many more lives would have been lost, but for the gallant efforts and bravery of African Star crewmen and others involved in the rescue and firefighting operations. A collision and fire of this magnitude must point up both weaknesses (areas where sea­men can learn from the mistakes of others) and strengths (examples of leadership, teamwork and heroism). Some of the more important les­sons to be learned include the following:

Whistle signals are not of themselves a re­liable means of communicating a vessel's passing or turning intentions. Bridge-to­ bridge radiotelephone communication on a single frequency would probably have prevented this tragedy. It is now required by law. Uncertainties and difficulties are experi­enced in applying the inland rules of the road to arrange a safe passing. Passing requires the use of visual and verbal com­munication in both directions, plus good judgment. A properly equipped vessel can with stand a serious collision and fire. A disciplined and well-trained crew can keep the vessel afloat, maintain control of the wheelhouse and engine room and successfully combat the lire. Leadership, courage and discipline are essential traits for officers and crewmen in the merchant marine. The value of these traits becomes most evident in an emer­gency situation such as a serious fire.