Blog 89 - A Marine Report of a Fire on a Different Self Unloader

One of the more important contingencies that a Chief Engineer needs to prepare for on a Self Unloader, is the prospect of fire in the Loop Belt spaces, Tranfer Belt spaces and Tunnel spaces. Because of the dust emanating from the cargo, Fire sensors become useless if installed. In fact, they become counter productive, with the dust triggering off alarms frequently. Heat sensors are partially effective.

In the loop spaces, only very narrow spaces on either side of the loop belt is available for to walk up or down the steel inclined ladders.

Fighting a fire in the Loop spaces under these restricted conditions becomes well nigh impossible, with the fire fighters having to move up narrow spaces, wearing heavy fire suits, SCBA sets and a charged fire hose. It is possible for them to get stuck in those spaces, under those extreme conditions, leading to loss of lives.

After nearly a month on board my first Self Unloader, the 'Citadel Hill', I sensed the inherent weakness in the system, in the Loop Belt area, in the event of a fire.

Fire lines providing sea water, fire line valves and fire hoses were in plenty in these spaces but would be of no use in the event of a fire, as one would not be able to gain access to these valves and hoses. They were okay for use in washing purposes, but useless in a fire.

There were water spray (Sprinkler) arrangements. We fabricated larger pipes for a more intense spray.

But, I felt that even this would not be sufficient in the event of a major fire.

The only alternative was constant physical surveillance to prevent a fire from starting when the cargo was being discharged and timely maintenance of suspected rollers and pillow block bearings. 'Training' the Loop Belt assumed great importance, to prevent the belt edges from rubbing against side rollers and inducing frictional heat.

Maybe the more modern Self Unloaders have temperature sensors on the larger bearings which are monitored from the Control Room.

Below is a summary of a different vessel's Transfer Belt spaces fire, a Marine Investigation Report, drawn up the Canadian Authorities, after a Transfer Belt spaces' fire on the Self Unloader "Ambassador".

The Transfer Belts system and construction have an innate flaw that can lead to fires, if not constantly checked and the root cause eliminated again and again y washing.

The Transfer Belts' are of very short lengths and, necessarily, steeply angled over this short length, so that they feed the Loop Belts . Some cargoes, like rock phosphate, have a tendency to stick to the belt and are carried over to the idle side of the belt after passing the main pulley. A return pulley on the idle side of the belt then catches some of the spill over, which accumulates within a few hours.

As this waste cargo build up continues, friction on the belt increases, as it rubs more and more on to the waste cargo. This is happening below the loaded area of the belt, on the returning (supposedly) empty belt.

This increase in friction could lead to a fire.

On later ships, a 'belt scrubber' is incorporated at exactly this spot, which literally scrapes the waste cargo off the belt. Many a time, I had to stop the plant during discharge in order to wash the scrubber itself.

Damaged pillow block bearings could be another cause of fire, if not responded to in time. Sea water (from washing) combined with damaged end seals of the pillow block bearings + the accumulation of cargo dust which enters past the damaged seals, prove to be a 'grinding paste' for the quick wear of the bearing. I have renewed many bearings because they were noisy and hot to the touch, finding the rollers of the bearings either missing or overly worn.

Pillow block bearings take a few hours to renew, for which cargo has to be stopped. As a temporary measure, I used to cool the bearing with a steady stream of fresh water from a small hose, till cargo is completed.

Marine Investigation Report M94M0057

Fire - in the cargo-handling conveyor system

of the self-unloading bulk carrier "AMBASSADOR"

Belledune, New Brunswick

31 December 1994

Summary

In the early morning hours of 31 December 1994, a fire broke out in the conveyor belt system of the "AMBASSADOR" during the unloading of a cargo of rock phosphate. The fire subsequently spread to the vessel's accommodation, and the combined efforts of the ship's crew and several shore-based fire departments were required to bring the fire under control before it was fully extinguished, some 28 hours later. There was no damage to harbour installations, no serious injury and no reported pollution as a result of the fire.

The Board determined that, when the conveyors were stopped, a section of one of the conveyor belts ignited, probably because the belt was in contact with an overheated roller. The roller probably overheated due to a bearing failure or to being jammed with refuse which ignited after contacting the overheated bearing.

1.2 History of Events

1.2.1 Prior to the Fire

Cargo unloading started at 1225

Footnote

on 29 December 1994, shortly after the vessel berthed at Belledune and was intended to be continuous. However, the rock phosphate cargo was found to be most difficult to retain on the conveyor belts and this, in conjunction with a drop of some 2 m between the cargo belts and the transfer belts, gave rise to a lot of dust in the vicinity of the transfer conveyors. There were frequent stoppages because spilled cargo had to be shovelled back on to the belts. Finally, although the tunnelmen were wearing paper face masks, the dust became too dense for work to continue, and, at 0115 on 31 December, it was decided to stop the unloading.

The gates to No. 5 hold, which was being discharged at the time, were closed, and, after inspection of the conveyor system, the crew members left the tunnel area with the intention of returning to resume unloading once the dust had settled. The entire, empty, conveyor system was left running. The operator left his position in the control room and met with the chief engineer on the weather deck to discuss the problem while the tunnelmen proceeded to the control room. A glance through a doorway in the loop belt casing revealed that the dust remained severe, and, because it was believed that the movement of the conveyor system was preventing the dust from settling, the system was stopped at 0205.

Fifteen minutes later, at 0220 (after personnel had left the area), a heat sensor in the transfer belt area (below and slightly forward of the loop belt) indicated a fire and, at about the same time, smoke was seen emanating from the open top of the loop belt casing.

1.2.2 Containing the Fire

After the general alarm went off, the water sprinkler system in the loop belt casing was started and all mechanical ventilation in the tunnel was stopped. The dense smoke prevented personnel from re-entering the area to determine the location of the seat of the fire and to fight the fire, but water from three of the ship's hoses was directed through doorways in the loop belt casing to supplement the sprinklers in an attempt to drench the transfer belt area below. Since all deck hydrants but one were frozen, two of the three hoses were led from hydrants in the engine-room through the accommodation to the loop belt casing.

The master notified the ship's agent of the fire by telephone. The agent and a shore worker, upon becoming aware of the fire, informed the security personnel at a factory in the port, who in turn alerted the fire department and various other community fire departments in the area. The master then contacted the managers, and the owners, who sent two directors to the scene and reportedly set up shore-based response teams to provide assistance in fire-fighting efforts. The fire chief arrived at 0300, followed by a Canadian Coast Guard (CCG) Ship Safety Branch surveyor at about 0530, and the two company directors later in the day. All assisted the master to a varying degree in fighting the fire and coordinating the efforts of the fire-fighters. The fire chief and the two directors remained on the scene throughout.

Heat transference through the engine-room bulkheads indicated that the seat of the fire was in the transfer belt area, and its intensification indicated that the application of water through the loop belt casing was unsuccessful. Following discussions between the master, the fire chief and the Ship Safety Branch surveyor, it was decided to attempt direct action by entering the transfer belt area through the hydraulically operated W/T door leading from the engine-room to the lower part of the loop belt casing. At 0625, a party of three persons opened the W/T door. One of them, dressed in standard fire-fighter's clothing and equipped with a spray nozzle hose, entered the loop belt casing. The heat and smoke forced him to withdraw before he could determine the location of the seat of the fire. A couple of areas on the forward bulkhead and loop belt casing in the engine-room later became so heated that paint on the engine-room side began to ignite in patches which was controlled by boundary cooling.

The heat and smoke also prevented the W/T door from being closed (the local controls having been rendered inaccessible), but the fire door, which was spring-loaded, closed automatically, and this prevented the fire from directly entering the engine-room. Repeated attempts were made to close the W/T door hydraulically using a remote control on the main deck, but this area had also become too hot for personnel. External fire-fighting was continued and supplemented by pumper trucks directing water through the open top of the loop belt casing. Sea water was also pumped into the empty No. 3 hold, running into the tunnel area through the gates and this, in conjunction with the other expended fire-fighting water, flooded the tunnel, eventually immersing the burning longitudinal cargo belts over up to 90 per cent of their lengths.

At 1100, the colour of the smoke began to change from black to grey, and it was believed that the fire had been brought under control. From that time, numerous attempts were made to reach the seat of the fire, but they were always thwarted by heat and smoke. However, at 1320, as no more smoke could be seen, it was believed the fire had been extinguished. At 1330, the ventilation fans were restarted with the intent of removing smoke and fumes so that persons could enter the space and deal with any remaining "hot spots". Until that time, the fire had been confined to the tunnel and conveyor belt system.

One hour later, at 1430, before personnel had entered the area, dense smoke again emanated from the loop belt casing and all external fire-fighting was resumed. The fire then burned to a greater intensity with heat transference through bulkheads igniting fires in the accommodation, despite pre-cooling with water. It took some 28 hours after the initial outbreak before the fire was fully extinguished; continuous shore assistance consisting of both personnel and material was provided throughout. The CCG vessel "SIMON FRASER" arrived on the scene shortly before noon on 01 January 1995 and stood by.

Post-fire examination of the accommodation revealed that some cabin doors were in the open position, which facilitated the spread of fire.

1.3 Injuries to Persons

One crew member suffered a minor case of smoke inhalation, and the master had a minor case of frostbite. While attempting to rig a hose on the superstructure, the attending Ship Safety Branch surveyor jumped onto a platform from a height of 0.9 m to 1.2 m (three to four feet), landed on uneven ice, slipped and injured his foot.

1.4 Damage

The vessel's self-unloading system was heavily damaged; both of the transfer belts and their associated controls and fittings were burnt out as was the interior of the loop belt casing. Some 25 to 30 m of both the port and starboard fore-and-aft belts was burnt, but the section of the loop belt below the transfer belts was not. The vessel's structure bordering the tunnel in way of No. 5 hold was distorted from the heat. A resulting spill of some 200 to 300 tonnes of cargo had to be cleared from the conveyor system before the fire site could be inspected. Approximately 25 per cent of the accommodation was destroyed in the fire with the balance sustaining smoke damage to differing degrees and some water damage. Paint was blistered on some sections of the forward engine-room bulkheads in patches which were common with the loop belt casing. In contrast, a set of oxyacetylene cylinders was discovered toward the after end of the tunnel, unaffected by the fire.

1.10 Possible Origin of the Fire

The report prepared by the TSB Engineering Laboratory states that "the fire or burn pattern was symmetrical from the engine-room bulkhead forward" which "strongly suggests that the fire progressed from the aft end of the tunnel forward."

Post-casualty inspections showed that the most intense heat had been centred in the area of the transfer belts. By process of elimination, it was determined that none of the electrical equipment or electrical and mechanical machinery had been the cause of the fire. Also, there had been no hot work (burning or welding) recently carried out in the area and there was no reason to suspect arson or smoking. Therefore, frictional heat was considered to be the most probable cause of the fire. The transfer conveyor belting and rollers in the area had been completely destroyed, but testing of similar belts and rollers under laboratory conditions at the TSB Engineering Laboratory determined that temperatures in excess of 400C were required to ignite the rubber-tired steel rollers and 450C to ignite the belting. These temperatures could not be reproduced by the small-scale frictional testing carried out at the laboratory, but the tests did show that it would be difficult for rollers or belting to be ignited by friction alone. It is most probable that an intermediary fuel source with a lower ignition temperature was involved.

Indications are that a roller overheated due either to a bearing failure or to being jammed with refuse such as discarded gunny sacking (ignition temperature at the lab of 193C) or nylon securing straps; the overheating causing and sustaining a fire for a period of time. As long as the conveyor system was running, the belting passed rapidly over the heated roller and/or burning refuse but did not ignite. However, when the belting was stopped, the heat source was constant in one area of the belting and sufficient to ignite it.

The TSB Engineering Laboratory report reveals that a TSB photographic record of the burn site shows that one of the end rollers on the starboard transfer conveyor was not properly seated in the support bracket, while the adjacent centre roller appeared to be secure. The report explains that this photographic evidence was not noted until after the assembly had been removed and, therefore, the roller was not available for further examination. However, the report continues that "typically, a bearing failure results in the collapse of the roller as the bearing support is lost" and that "as the bracket appears to be still supporting the centre roller, the displacement of the end roller probably required the failure of the end roller's axle." The report concludes that "Although the origin and cause of the fire ... were not conclusively determined, it is probable that the fire originated in the starboard transfer conveyor and was caused by the heat generated when a bearing failed, seizing and eventually displacing a roller from the idler frame."

1.11 Ventilation of the Tunnel Area

The ventilation system consisted of two blower fans in the forward part of the tunnel and two extractor fans at the after end which had proved adequate when unloading less dusty cargoes. There was no dust-removal or air filtration system. Reportedly, the fans were operating, but it could not be determined if they were operating to capacity. In any case, their major function was to provide a continuous flow of fresh air to the area, not to remove or filter out dust.

The paper face masks worn by the tunnelmen proved inadequate in providing sufficient filtered air to the wearers. The use of the vessel's compressed air packs to provide the tunnelmen with fresh air had been discussed, but not implemented. The air packs, designed to provide air to the fire-fighters for a limited period of time, are part of the vessel's fire-fighting equipment. When the fire broke out, no decision had been taken as regards putting the air packs to a use other than their designed use.

1.12 Loop Belt Casing Structure

Entrances to the tunnel area could be closed off to assist in reducing air flow to the area. However, air was free to flow through the top of the loop belt casing through which the cargo was lifted by the loop belts, and a restricted amount of air could enter through the imperfectly closing hopper gates at the bottom of hopper No. 3. Both of these conditions would allow air to provide oxygen to the fire.

A W/T door provided access to and from the engine-room to facilitate maintenance/repairs and was intended, when closed, to retain the watertight structural integrity of the ship. The remote-closing position on deck was provided as a precautionary measure should the engine-room become inaccessible following collision or in other emergency situations. A spring-loaded fireproof door had been fitted in conjunction with the W/T door.

1.13 Cargo

Rock phosphate is a mined natural product which is not hazardous inasmuch as it is not ignitable, toxic nor hazardously reactive to other materials. In this instance, it was carried in bulk in all of the holds and was in the form of granules, a large proportion of which had broken down into fine dust. This cargo was described as, by far, the dustiest and the most difficult to retain on the conveyor belts of all cargoes which had been unloaded during previous trips. Recent cargoes carried by the "AMBASSADOR" had been homogeneous but varied, consisting of coal, limestone, gypsum and rock phosphate.

Stoppages caused by spilled cargo reduced the rate of discharge to an average of some 240 tonnes per hour during the 36½ hours preceding the outbreak of the fire, whereas continuous discharge could have attained a rate of some 1200 tonnes per hour, the maximum rate requested by the shore plant. The vessel's unloading system was capable of delivering 4000 tonnes per hour. The conveyor belts can be run at two speeds and are normally run at the faster of the two. The crew regulates the amount of cargo being discharged by adjusting the gates at the bottom of the cargo holds.

1.14 Housekeeping in the Tunnel Area

During the investigation, a great deal of discarded material was found in the areas of the tunnel which had not been affected by the fire. This material consisted of gunny sacking and nylon straps used to cover the hopper gates to prevent cargo spillage during the voyage, together with various bits of wood, empty paint cans, etc.

1.15 Vessel Stability

In order to assess the effects of the fire-fighting water which accumulated in the cargo conveyor tunnel, the post-casualty stability report

Footnote

4 analysis focused on establishing the vessel's intact transverse stability characteristics on arrival and also after the fire was extinguished. Comparisons were then made with the regulatory minimum intact stability criteria included in the vessel's Trim and Stability Booklet, as approved by the CCG on 13 February 1984.

Water used to fight the fire in the accommodation quickly escaped from the various decks via the elevator shaft and, because this water was not retained on the upper decks, it caused no significant rise of the vessel's vertical centre of gravity (VCG).

Calculations show that expended water from the fire-fighting plus water used to flood the tunnel and submerge the conveyor system (calculated at some 2244 tonnes), together with the filling and pressing up of two ballast tanks with a further 5746 tonnes of ballast water, lowered the partially unloaded vessel's VCG and more than compensated for the virtual rise of G attributable to the free-surface effect of the water retained in the tunnel area. The calculations revealed that the vessel's intact transverse stability characteristics on arrival, during the fire-fighting effort and after the fire was extinguished, exceeded the minimum safety criteria as specified in the regulations.

Under the still water conditions of the harbour where the ship was not subjected to external wave forces causing rolling or pitching motions, there was no danger from dynamic surging and free-surface effect, and positive initial stability was retained, even though a list of 2.5 developed.

There was no tunnel sounding or calibration table to assist in accurately ascertaining the precise weight, or free-surface area, of the water in the tunnel: an estimate made during fire-fighting gave 1000 tonnes, but post-casualty calculations based on the water marks throughout the tunnel together with calculations based on the final load condition of the ship, determined that there had been some 2244 tonnes of water in the tunnel area.

3.0 Findings

During unloading, considerable difficulty was experienced in preventing cargo from spilling from the conveyors.
The dust from spilled cargo in the tunnel was so thick that crew members found it necessary to suspend the unloading and leave the area.
The empty conveyor belt system was stopped, pending the resumption of the unloading operation.
A section of the stationary conveyor system came into contact with a heat source that caused the belting to ignite.
The fixed sprinkler system in the loop belt casing was ineffective in controlling a major fire.
The open top of the loop belt casing and the hopper gates to No. 3 hold, which were not airtight, allowed a continuous supply of oxygen to the fire.
The preparations of the vessel's fire main for operation in cold weather proved ineffective in the existing extreme conditions and all deck hydrants but one were frozen.
Additional hoses had to be led from engine-room hydrants through the accommodation to the loop belt casing.
After being opened in an unsuccessful attempt to fight the fire, the watertight (W/T) door between the engine-room and the tunnel could not be closed.
A spring-loaded fireproof door on the engine-room side of the W/T door closed automatically and prevented the fire from directly entering the engine-room.
Intentional flooding of the tunnel was instituted to extinguish fires in that area.
Compensatory ballasting, supplementing the partial discharge of cargo, ensured that the vessel maintained positive initial transverse stability when the tunnel was flooded.
The vessel's stability information gave no guidance on the effect of flooding the tunnel on the vessel's stability.
The routine maintenance and testing regime of safety equipment proved ineffective.
The crew had not been drilled in fire-fighting during weekly emergency musters and was consequently unaware of the condition of the equipment.
Although the vessel had passed a safety equipment inspection by a classification society surveyor only two months earlier, some of the shipboard fire-fighting equipment was sub-standard.
The Port Authority had not provided the ship with instructions on emergency alert procedures.
The Port Authority did not require a fire plan to be available and accessible to shore-based fire-fighters.
None of the shore-based fire-fighters had been trained in fighting shipboard fires.
There were no shore fire cabinets close to the scene of the fire.
The Canadian Coast Guard (CCG) had earlier declined to approve or endorse the owners' plan to upgrade the fire-fighting installation in the self-unloading system due to the absence of guidelines or regulatory requirements.
Housekeeping standards in the work area were such that the debris in the tunnel compromised safety.
Open fire doors in the accommodation facilitated the spread of fire between cabins.
The extreme cold weather conditions hampered the fire-fighting efforts.

3.1 Causes and contributing factors

When the conveyors were stopped, a section of one of the conveyor belts ignited, probably because the belt was in contact with an overheated roller. The roller probably overheated due to a bearing failure or to being jammed with refuse which ignited after contacting the overheated bearing.

===== Continues in Blog 80 === "Marine Musings 26" begins =====

Blog 89 - A Marine Report of a Fire on a Different Self Unloader - Must Have Been Frightening