Chapter 2
Past Natech Events
E. Krausmann*
Abstract
Numerous past Natech accidents are testimony to the dangers that can arise when the natural and technological worlds collide. Past experience also teaches that Natech accidents can in principle be triggered by any kind of natural hazard and that it does not necessarily require a major natural-hazard event, such as a strong earthquake or a hurricane, to provoke the release of hazardous materials. In fact, Natech accidents were often caused by rain, lightning, or freeze, to name a few. This chapter provides selected examples of past Natech events to show the wide variety of natural hazard triggers and also the multitude of hazardous target infrastructures.
Keywords
Natech accident
case study
earthquake
tsunami
flood
lightning
storm
volcano
refinery
pipeline
offshore infrastructure
oil spill
Numerous past Natech accidents are testimony to the dangers that can arise when the natural and technological worlds collide. Past experience also teaches that Natech accidents can in principle be triggered by any kind of natural hazard and that it does not necessarily require a major natural-hazard event, such as a strong earthquake or a hurricane, to provoke the release of hazardous materials. In fact, Natech accidents were often caused by rain, lightning or freeze, to name a few. This chapter provides selected examples of past Natech events to show the wide variety of natural hazard triggers and also the multitude of hazardous target infrastructures.
2.1. Characteristics of Natech events
The extent and consequences of Natech accidents have often reached major proportions, indicating low levels of preparedness. The reasons are manifold and cannot be attributed to a single determining factor. The main difficulty probably stems from the fact that Natech risk reduction is fundamentally a multidisciplinary topic that cuts across traditional professional boundaries. In addition, Natech risk is still considered somewhat of an emerging risk that has only been receiving more attention after a number of recent major accidents. As a consequence, there is still a lack of dedicated knowledge on the dynamics of Natech accidents and not much guidance for industry and authorities on how to address this type of risk. This makes scenario development for planning purposes very difficult.
Another factor is the misconception that engineered and organizational protection measures implemented to prevent and mitigate the so-called conventional industrial accidents would also protect against Natech events. However, Natech accidents differ significantly from those caused by, for example, mechanical failure or human error, and therefore require targeted prevention, preparedness, and response activities.
For instance, when impacting hazardous installations, natural hazards can trigger multiple and simultaneous loss-of-containment (LOC) events over extended areas within a very short timeframe. This was observed repeatedly in areas hit by strong earthquakes where it has posed a severe strain on emergency responders who are usually not trained and equipped to handle a large number of hazardous-materials (hazmat) releases simultaneously. In these situations, the risk of cascading events is high.
Furthermore, the very natural event that damages or destroys industrial buildings and equipment, can also render inoperable engineered safety barriers (e.g., containment dikes, deluge systems) and lifelines (power, water for firefighting or cooling, communication) needed for preventing an accident, mitigating its consequences, and keeping it from escalating. This can complicate the successful containment of hazmat releases.
In case of strong natural disasters with releases of dangerous substances, simultaneous emergency-response efforts are required to cope with the consequences of the natural disaster on the population and the Natech accident that poses a secondary hazard. This undoubtedly leads to a competition for scarce resources, possibly leaving some urgently needed response mechanisms unavailable. The hazmat releases can also hamper response to the natural disaster when toxic substances, fires, or explosions endanger the rescue workers themselves. During some Natech accidents an evacuation order was issued to first responders when their lives were in danger, which sometimes meant leaving behind people who were trapped in residential buildings and in need of help.
Another complicating factor is that civil-protection measures, commonly used to protect the population around a hazardous installation from dangerous-substance releases, may not be available or appropriate in the wake of a natural disaster. For instance, in case of toxic releases during conventional technological accidents, residents in close proximity to a damaged chemical plant would likely be asked to shelter in place and close their windows. This measure would not be applicable after an earthquake as the integrity of the residential structures might be compromised. Similarly, evacuation might prove difficult in case roads have been washed away by a flood or are obstructed by a landslide.
These examples clearly show how the characteristics of Natech events differ significantly from those of conventional technological accidents both in terms of prevention and mitigation. They also highlight why the management of Natech accidents can be challenging without proper planning, and it clarifies why dedicated assessment methodologies and tools are necessary for addressing this type of risk.
2.2. Kocaeli Earthquake, 1999, Turkey
The Mw 7.4 Kocaeli earthquake in Turkey occurred at 3 a.m. on Aug. 17, 1999. The earthquake killed over 15,000 people and left over 250,000 homeless. The earthquake affected an area of 41,500 km2 from west Istanbul to the City of Bolu (Tang, 2000). Modified Mercalli Intensity (MMI) values for the Kocaeli earthquake ranged from VIII to X. Roads, bridges, water distribution, power distribution, telecommunications, and ports were also heavily damaged by the earthquake (Steinberg and Cruz, 2004). The affected area was densely populated and the most industrialized region of the country. Not surprisingly, the earthquake damaged more than 350 industrial firms in the Izmit Bay area and resulted in multiple hazardous-materials releases. Cruz and Steinberg (2005) reported that releases occurred from about 8% of industrial plants subject to MMI≥IX.
Steinberg and Cruz (2004) carried out field visits and interviews in the affected areas about a year after the earthquake. The authors visited and analyzed hazardous-materials releases at 19 industrial facilities impacted by the earthquake. They found that 18 of the facilities they visited suffered structural damage, while 14 reported hazardous-materials releases during or immediately following the earthquake. The authors reported that nine of these facilities suffered severe chemical releases, while an additional five had only “minor” releases with little or no adverse effects. It is important to note that some facilities reported multiple releases.
Steinberg and Cruz (2004) identified over 20 cases of hazardous-materials releases in their study. They found that structural failure as the primary cause of the release was reported in six of the 14 facilities that had hazardous-materials releases. Eleven facilities reported liquid sloshing in storage tanks, while nine of these plants indicated that liquid sloshing was the main cause of hazardous-materials releases at their plant. The authors found that damage to containment dike walls resulted in spills in four of six cases while rupture of pipes and connections led to chemical releases in six out of 12 cases. The most important hazardous-materials releases they reported include:
• The intentional air release of 200,000 kg of anhydrous ammonia at a fertilizer plant to avoid tank overpressurization due to loss of refrigeration.
• The leakage of 6.5 million kg of acrylonitrile. The acrylonitrile was released into air, soil, and water from ruptured tanks and connected pipes at an acrylic fiber plant.
• The spill of 50,000 kg of diesel fuel into Izmit Bay from a broken fuel-loading arm at a petrochemical storage facility.
• The release of 1.2 million kg of cryogenic liquid oxygen caused by structural failure of concrete support columns in two oxygen storage tanks at an industrial gas company.
• The multiple fires in the crude-oil unit, naphtha tank farm, and chemical warehouse, the exposure of 350,000 m3 of naphtha and crude oil directly to the atmosphere, and the LPG leakages and oil spills at the port terminal at an oil refinery.
In the following sections, two major Natech accidents triggered by the Kocaeli earthquake are described. The accident reports are based on personal communication with refinery officials, municipal fire fighters, and other responders during field visits carried out in 2000 and 2001, and work published by Steinberg and Cruz (2004), Cruz and Steinberg (2005), and Girgin (2011), unless otherwise indicated.
2.2.1. Fires at a Refinery in Izmit Bay
2.2.1.1. Accident Sequence and Emergency Response
The affected refinery was operating at full capacity at 3 a.m. the morning the earthquake occurred. The refinery was subjected to strong ground motion, surface faulting, and a tsunami wave (Tang, 2000; Tsunami Research Group, 1999). The combined earthquake effects resulted in three fires and multiple hazardous-materials releases at the refinery. The first fire occurred at the facility’s chemical warehouse. It is believed that chemicals stored on the shelves fell down due to the strong ground motion, breaking glass containers and resulting in the spreading and possible mixing and reacting of the released chemicals. The fire, which was ignited either by sparks or by exothermic chemical reactions, was extinguished in less than half an hour (Girgin, 2011; Steinberg and Cruz, 2004).
The second fire started at the crude-oil processing plant due to the structural failure and collapse of a reinforced concrete stack tower measuring 115 m. The collapsed stack fell over the crude-oil charge heater and a pipe rack, breaking 63 product and utility pipes. The fire, which started when the highly flammable substances found in the pipes ignited, was put out by fire-fighters after 4 h, reignited around noon, was extinguished again, and then reignited again at about 6 p.m. on the same evening of the earthquake. The fire kept reigniting due to the continued supply of fuel from the broken pipes. The number of shut-off valves on the product pipelines was insufficient in the vicinity of the charge heater, and flow from the product lines could not be stopped.
The third fire occurred at the refinery’s naphtha tank farm (Fig. 2.1). Four floating roof naphtha storage tanks were simultaneously ignited following the earthquake. The fires were caused by sparking resulting from metal-to-metal contact between the metallic seals and the tank walls due to the bouncing of the floating roofs against the inner side of the tanks. The earthquake also caused damage to a flange connection in one of the tanks which resulted in naphtha leakage into the refinery’s internal open-ditch drainage system. The fire on the roof spread to the flange connection and through the drainage system to two more naphtha tanks about 200-m away.
Control of the fires was difficult due to the competing fires ongoing at the refinery. Initially, the fires were brought under control, but this was only temporary. Multiple fire-fighting teams arrived to provide support (e.g., from the military, the municipalities, and neighboring facilities). Nonetheless, the fire-fighting teams lost control of the fire due to the major conflagration and had to retreat. Efforts to control the fire were made by land, sea, and air. The loss of electricity and shortage of foam chemical hampered the response activities. Flyovers to throw seawater and foam over the fires were carried out by forest-fire- and carrier airplanes. However, these efforts were also not effective as it was not possible to fly low enough to approach the fires. Fire-fighting operations were abandoned at around 7 p.m. the day of the earthquake, and an evacuation order was issued by the crisis center for a zone of 5-km around the refinery.
The Turkish government requested international assistance, which arrived on the second and third days. Efforts were concentrated on preventing the fires from spreading to other parts of the plant and nearby chemical installations.
2.2.1.2. Consequences
Direct impacts and cascading events resulted in severe consequences at the refinery, and had repercussions offsite. The collapsed stack heavily damaged the crude-oil processing plant and pipe rack resulting in a large fire that took hours to control. According to Kilic and Sozen (2003), the stack tower collapsed not due to lack of strength caused by design or material deficiencies but due to the presence of reinforcing-bar splices in the region where flexural yielding occurred.
At the naphtha tank farm, six naphtha tanks were completely destroyed burning 30,500 t of fuel. The fires also damaged five additional storage tanks due to fire impingement. Heat radiation burned one of the two wooden cooling towers at the plant. The second cooling water tower collapsed due to the earthquake, also affecting the connected water pipes which in turn slowed down fire-fighting efforts. The LPG, crude oil, and gasoline storage tanks at the refinery, a large ethylene storage tank at a neighboring facility, and two large refrigerated ammonia gas tanks at a fertilizer plant nearby were unaffected by the fire. However, the ammonia tanks were intentionally vented to avoid overpressurization due to the loss of refrigeration capabilities caused by the earthquake.
All in all, the earthquake damaged a total of thirty storage tanks in the naphtha, crude oil, and LPG tank farms. Typical damage to naphtha and crude-oil tanks included elephant-foot buckling of tank walls, bulging of tank tops due to liquid sloshing, cracking of tank roof-shell wall joints, and damage to roof seals. Damage to roofs resulted in exposure of more than 100,000 m3 of naphtha, and over 250,000 m3 of crude oil directly to the atmosphere, increasing the threat of additional fires (Cruz, 2003). Cruz (2003) reported that all the legs of the pressurized LPG steel tanks were twisted severely, resulting in an LPG release from a broken flange connection. There was no ignition of the LPG reported at the refinery. However, two truck drivers were killed in a fire from the gas leak just outside the refinery. The fire was believed to have been triggered by an ignition source from one of the trucks (EERI, 1999).
The earthquake also caused extensive damage to the refinery’s port facilities, and onsite utilities. Several large-diameter pipelines located near the shoreline, used to transport crude oil from tankers to the storage tanks, fell from their concrete supports but did not break. The loading and unloading jetty was damaged heavily resulting in an oil spill. Nonetheless, sea pollution was largely attributed to oily water runoff from the fire-fighting efforts (Girgin, 2011).
2.2.1.3. Lessons Learned
The multiple fires in the naphtha tank farms called for a reevaluation of floating-roof systems to ensure that during strong ground shaking no metal-to-metal contact occurs. Liquid sloshing caused the sinking of roofs and extensive damage to tanks. While liquid sloshing cannot be prevented, storage tanks can be reinforced to make certain that they do not suffer deformation due to the lateral forces induced by the sloshing liquid.
The spreading of the fires through the internal drainage canal indicates the need for a system of shut-off doors in internal drainage canals to keep spilled oil from entering public areas such as water bodies, sewer systems, or other parts of the plant.
The inability to control the fire at the crude-oil processing unit stemmed from the fact that there were insufficient shut-off valves to stop the flow of flammable materials through the broken pipes. The installation of emergency shut-off valves in critical segments of pipelines is recommended.
Other major problems observed during the Natech accidents at the refinery concerned failures regarding mainly mitigation and emergency response to the Natech accidents. Girgin (2011) summarized these problems based on work by Kilic (1999) as follows:
• lack of foaming systems at the tanks,
• inadequate power generators,
• inadequate diesel pumps,
• limited application of sprinkler systems,
• noninteroperable fire-fighting water connections,
• insufficient containment ponds,
• lack of fire-fighting towers, and
• deficiencies in the coordination and management of the fire-fighting activities.
Based on the lessons identified from these Natech accidents, Girgin (2011) reports that corrective measures have been taken at the refinery since the earthquake. A revision of the emergency-response plan was made taking Natech events into consideration. In particular, the plan now considers the possibility of multiple accidents simultaneously. In order to secure proper coordination and emergency management, regular meetings with all refinery personnel are now held every 2 months to discuss emergency-response practices based on probable scenarios that include Natech risks. Several improvements were made to ensure that there is adequate fire-fighting water supply (e.g., the water capacity was increased and a seawater connection was introduced to the fire-fighting water system) and adequate fire-fighting equipment (e.g., portable diesel pumps with increased capacity, increased length of water hoses, upgrade of fire-fighting vehicles, fixed and mobile water cannons). Water sprinkler and foaming systems have been installed at all tanks. Other measures that have been taken include the installation of gas and flame sensors for the detection of gas leaks and fires, and the maintaining of a higher length of oil containment booms in the case of spills into the sea. The refinery has used the experience from these Natech accidents to learn and improve their disaster preparedness.
2.2.2. Hazardous-Materials Releases at an Acrylic Fiber Plant
2.2.2.1. Accident Sequence and Emergency Response
At an acrylic fiber plant located in Yalova on the south shore of the Marmara Sea, acrylonitrile (AN), a highly toxic, flammable, and volatile liquid, was stored in eight fixed-roof steel tanks at the time of the earthquake. Of these, three partly full tanks suffered major damage during the earthquake from which AN was released. The releases occurred due to sloshing of the liquid in one partly full tank, buckling of the roof in another tank exposing the chemical to the atmosphere, and from a broken outlet pipe in the third tank. 6.5 million kg of AN were released. Simultaneously, the earthquake cracked the concrete containment dikes around the AN tanks, which allowed the leaked chemical to flow through the containment dikes into the plant’s storm-water drainage channel and to the Bay of Izmit.
The emergency response to the AN spill was complicated due to external power outage, damage to the plant-internal power generation turbine, loss of communications, and impassable roads due to debris from the earthquake impact on buildings and roads. Considering that AN is highly volatile and flammable, emergency-power generators strategically placed near the tanks were not started as there was concern that a spark could ignite the AN vapors. Emergency generators and pumps had to be moved to a safe place before they could be put into operation. Fortunately, there were no fires as a result of the AN spill.
Emergency response consisted in applying foaming chemical mixed with water to the release to prevent vaporization. However, the application of foam was delayed due to a loss of water supply as the main water line in the city of Yalova had been damaged by the earthquake. External emergency responders from Yalova and the air force arrived on the same day, but the responders could not enter the spill zone because they did not have appropriate clothing or breathing apparatus to protect them from the harmful effects of the toxic chemical. Eventually, the chemical plant ran out of foaming agent and requested additional supplies from the government and nearby industrial facilities. Additional foam and other resources were brought in by sea or by helicopter. The release was finally contained 48 h after the earthquake (Girgin, 2011; Cruz, 2003).
2.2.2.2. Consequences
Environmental effects were observed as a result of the AN leakage into the air, soil, ground water, and the sea. AN air concentrations were lethal to all animals at a small zoo inside the facility about 200 m from the tanks. Dead vegetation in an area of the same radius was also observed, and domestic animals were reportedly killed in nearby villages (Girgin, 2011; Cruz, 2003). There was also a fish kill reported due to the leakage of AN into Izmit Bay (Türk, 1999).
Poisoning symptoms were reported in the nearby villages and included hoarseness, vertigo, nausea, respiratory problems, skin irritation, headache, eye and nasal irritation (Girgin, 2011; Şenocaklı, 1999). A survey among the residents of Altinkum, which lies about 650 m away from the facility, found that the majority of respondents suffered acute toxicity effects. Less severe effects were reported by residents living as far as 2 and 2.5 km from the facility (Emiroğlu et al., 2000). It was also reported that 27 response workers were poisoned, one member of the military fire-fighting team went into a coma, while others team members were seriously affected (Girgin, 2011).
The toxic release and the subsequent evacuation order given by local authorities hampered search and rescue operations, which were mainly conducted by local people due to a lack of professional search and rescue teams. Similar to the case around the refinery discussed in Section 2.2.1, the evacuation order resulted in local people having to abandon search and rescue of family members, friends, and neighbors.
Soil contamination problems became apparent when harvested products in the affected areas that were put on the market were found to be contaminated with AN. The local government had to issue a ban on the agricultural products of the affected areas (Girgin, 2011).
The groundwater under the tanks reached AN concentrations in the thousands of ppm. After about a year of continuous application of a pump-and-treat regimen, the concentrations had dropped into the hundreds of ppm. There was concern, however, about the long-term effects of AN on the ecosystem of the Bay of Izmit as well as on the affected population.
2.2.2.3. Lessons Learned
The simultaneous damage to three AN storage tanks demonstrated the need for improved storage-tank design to resist the strong ground motion. During the reconstruction, the AN tanks were strengthened against sloshing effects and secondary roofs were constructed to minimize evaporation in case of a leak. Flexible pipe connections between storage tanks and pipelines were introduced to minimize leakage during earthquakes. Containment dikes were lined with impermeable materials and concrete dikes were reinforced. Fire-fighting foam spraying systems were installed around the perimeter of the containment dikes as shown in Fig. 2.2.
Figure 2.2 New Foam Spraying System Secured Along a Reinforced Concrete Containment Dike Photo credit: A.M. Cruz.
Other important measures adopted based on lessons from the accident included an increase in the capacity of emergency power generators. Furthermore, to avoid a fire or explosion, electrically classified power generators, ventilators, and pumps were installed. The location of fixed as well as mobile equipment was carefully evaluated to maximize emergency response when needed. Emergency- response plans were reviewed and improved to consider Natech scenarios.
2.3. Tohoku Earthquake and Tsunami, 2011, Japan
On Mar. 11, 2011, an Mw 9.0 undersea megathrust earthquake off the Pacific coast of Tohoku shook large parts of Japan. The Tohoku or Great East Japan earthquake not only affected a large number of hazardous installations, causing the release of hazardous materials, it also triggered a tsunami of unexpected magnitude which led to even more damage and destruction among chemical facilities. A field survey carried out by the Japanese Fire and Disaster Management Agency found damage at 1404 oil-storage or petrochemical plants due to the earthquake, although no details on the number and type of hazmat releases were provided (Nishi, 2012). In a parallel survey, the Japanese Nuclear and Industrial Safety Agency collected information on damage and in some cases hazmat releases at 50 high-pressure gas facilities and 139 cases of damage in other hazardous facilities (Wada and Wakakura, 2011).
Also other types of structures processing or housing dangerous substances were affected by the earthquake. For instance, in Ibaraki Prefecture, a tailings impoundment full of mining waste containing arsenic failed during the earthquake due to liquefaction. As a consequence, 40,000 m3 of toxic waste were released that flowed into nearby fields and a river, and eventually reached the coast (JX Nippon Mining and Metals, 2012). According to newspaper reports, the toxic concentration of the released tailings exceeded the value considered safe 25-fold (Asahi Shibun, 2011).
Numerous hazmat releases occurred during the Tohoku earthquake and tsunami. In some cases several Natech accidents were triggered at the same time in the same chemical plant, which led to multiple and simultaneous releases of dangerous substances. In addition, the tsunami aggravated the impacts of earthquake-triggered toxic or flammable releases by washing them away with the floodwaters and spreading them over wide areas. Nonetheless, considering that the management of the tsunami impacts and the nuclear emergency in Fukushima were the first and foremost priority, chemical releases were secondary unless they posed a concrete threat to the population or emergency responders. As a consequence, only very little information on hazmat releases and their impact is available, with the exception of a few major Natech accidents that are well documented.
In the following sections, two major accidents (one triggered by the Tohoku earthquake, one by the tsunami) will be described in detail. Unless specifically indicated, the information is based on interviews with competent authorities and emergency responders who were on duty at the time of the disaster, and on public information documented in Krausmann and Cruz (2013). Supplementary information was made available by the operator of one of the affected refineries (Cosmo Oil, 2011).
2.3.1. Fires and Explosions at an LPG Storage Tank Farm in Tokyo Bay
2.3.1.1. Accident Sequence and Emergency Response
The LPG storage tank farm where the Natech accident occurred is part of a refinery located on the eastern shore of Tokyo Bay. The refinery, which went into operation in 1963, has a production capacity of 220,000 barrels/day (b/d). In addition, it has a total storage capacity of 2,323,000 kL (crude oil, finished and semiprocessed products, lubricating oil, asphalt, and LPG), as well as 26,400 t of sulfur. In Mar. 2015, the maximum LPG storage volume was 46,900 kL in 21 tanks.
The accident was initiated in LPG Tank No. 364, which at the time of the earthquake was under regulatory inspection. As a consequence, it was filled with water instead of LPG to remove air from inside the tank. The main earthquake shock with a peak ground acceleration of 0.114 g caused several of the diagonal braces supporting the tank legs to crack. During the 0.99 g aftershock half an hour later, the legs buckled and the tank collapsed, thereby severing the connected LPG pipes and causing flammable LPG releases (Fig. 2.3). The tank met all earthquake design requirements for the area assuming LPG filling. However, with water being 1.8 times heavier than LPG, the support braces and tank legs could not withstand the additional loading due to the earthquake forces. This situation had not been considered in the tanks’ design requirements.
Figure 2.3 The Refinery’s Tank 364 That Collapsed During the Earthquake
The buckled legs are clearly visible. Photo credit: H. Nishi.
The buckled legs are clearly visible. Photo credit: H. Nishi.
The LPG leaking from the ruptured pipes spread and eventually ignited. With the fires heating up the tank contents, the tank adjacent to Tank 364 suffered a boiling liquid expanding vapor explosion (BLEVE), spreading the fire from tank to tank and eventually throughout the whole LPG tank farm. At least five associated explosions were documented at the refinery, the biggest of which created a fireball of about 600 m in height and diameter (Fig. 2.4). Human error contributed to the disaster as a safety valve on one of the LPG pipes had been manually locked in the open position to prevent it from actuating due to minor air leakages during repair work. Once the released LPG ignited, the valve could not be reached and closed, thereby continuously providing LPG to feed the fire. This exacerbated the accident and made the fires burn out of control. By manually overriding the emergency valve, the company was in violation of safety regulations. In a personal communication, the Chiba Prefecture Fire Department expressed its belief that the accident might have been manageable had the safety valve not been locked open.
Figure 2.4 Fireball at the LPG Storage Farm With a Diameter of About 600 m Photo credit: National Research Institute of Fire and Disaster, Japan.
Debris impact from the exploding LPG tanks damaged asphalt tanks located adjacent to the LPG storage area, causing asphalt to leak onto the ground and into the ocean. Moreover, burning missile projection, and dispersion and ignition of LPG vapors triggered fires in the adjacent premises of two petrochemical corporations. These secondary accidents released methyl ethyl ketone (MEK) and polypropylene. No supporting information could be found for a newspaper report claiming that the heat impingement from the LPG storage blaze sparked a fire in a warehouse containing depleted uranium.
The fires at the LPG storage tank farm were extinguished only after 10 days when the LPG supply was depleted. The emergency-response teams, which comprised on-site, local, regional, and national fire-fighting teams, worked from both land and sea. However, due to the many release sources it was decided to let the tanks burn until the fuel was exhausted. In addition, first responders sprayed water on the burning tanks to accelerate LPG evaporation. The company’s emergency-response plan did not take this type of scenario into account, and neither the company itself nor the Chiba competent authorities were by their own admission prepared for an accident of such magnitude.
2.3.1.2. Consequences
The accident caused six injuries at the refinery, one of which was severe. Three injuries were reported in the facility adjacent to the LPG tank farm where a fire was triggered via domino effect. The fires and explosions forced the evacuation of 1142 residents in the vicinity of the industrial area. Pieces of tank insulation and sheet metal were later found at a distance of over 6 km from the refinery and well inside residential areas. Air-quality monitoring in Ichihara Municipality did not indicate excessive amounts of air pollutants due to the fires at the LPG storage tank farm. Overall, there is very little information on the environmental impact of the event, although some asphalt seems to have entered the sea. However, the company indicated that all asphalt was successfully recovered and they highlight that there is no lasting impact on air, water, or soil from the accident.
The accident resulted in significant damage on-site, destroying all 17 storage tanks (Fig. 2.5). The LPG tank farm had to be completely rebuilt and the refinery returned to full operations only in Jul. 2013, more than 2 years after the accident. The explosions also damaged nearby vehicles and ships, and the shock waves broke windows and damaged shutters and roof shingles in nearby residential areas.
Figure 2.5 The Refinery’s LPG Tank Farm After the Fires and Explosions Triggered by the Tohoku Earthquake
Note the damaged asphalt tanks in the upper left corner of the image. © 2012 Google, ZENRIN.
Note the damaged asphalt tanks in the upper left corner of the image. © 2012 Google, ZENRIN.
In terms of economic losses, the refinery reported a loss on disaster of $US 72 million (based on the average 2011 Yen → $US exchange rate) for the fiscal year 2010 which ended in Mar. 2011. For fiscal year 2011, the company posted a net deficit of $US 114 million, largely due to the suspension of operations at the refinery and associated alternative supply costs.
2.3.1.3. Lessons Learned
Locking the safety valve in the open position in violation of safety regulations caused the accident to escalate out of control. This highlights the importance of adhering to and monitoring safety systems and measures at installations with a major-accident potential. As a consequence of the accident, the company has abandoned the practice of locking the emergency shut-off valve open and it carries out inspections to ensure that all personnel are aware of applicable laws and regulations. In addition, the refinery has ramped up preparedness activities for large-scale disasters by organizing emergency drills.
Another factor in the chain of fortuitous events that led to the disaster regards the filling of LPG tanks with water during inspections. It is considered good practice to not leave the water in the tanks for more than 2–3 days. However, Tank 364 had been filled with water for 12 days already at the time of the earthquake. The company has also addressed this issue by minimizing the time tanks remain filled with water.
From a technical point of view, the tank braces have shown to be the weak point of the structure during earthquake loading. Following the disaster, the LPG tank braces were reinforced to increase the resistance of tanks to potential future earthquakes.
2.3.2. Fires at a Refinery in the Sendai Port Area
2.3.2.1. Accident Sequence and Emergency Response
The refinery is located in the port area of Sendai and has a production capacity of 145,000 b/d. In Mar. 2011 it was subject to both earthquake and tsunami impact. The refinery automatically shut down at a PGA of 0.25 g. The PGA sensors stopped measuring at 0.45 g although it is believed that the actual PGA on site was higher. The inundation depth at the refinery was between 2.5 and 3.5 m.
Multiple accidents occurred at the refinery at the same time. When the tsunami hit, a tanker truck was in the process of loading hydrocarbons in the western refinery section. The truck toppled over and a pipe broke near the truck. Gasoline was continuously released from the break and eventually ignited from sources unknown. Sparking from the truck’s battery or static electricity have been advanced as hypotheses. The blaze destroyed the entire (un)loading facility and also engulfed sulfur, asphalt, and gasoline tanks. One gasoline tank was completely melted, others were partially melted and tilted (Fig. 2.6).
Figure 2.6 Burned Tanks at the Sendai Refinery Hit by the Tsunami Photo credit: C. Scawthorn.
In the same refinery section the tsunami caused multiple pipeline breaks with hydrocarbon releases, as well as many flammable leakages from broken pipe connections, which also ignited. The rail-tank loading area was also hit by the tsunami, with some rail cars being overturned by the water and burned by the fires. A significant portion of the refinery’s western section was consumed by the flames.
In another two places in the refinery heavy oil was released (Fig. 2.7). In one case, direct tsunami impact damaged a pipe connected to a tank close to the shore that was used for loading ships, spilling 4400 kL of heavy oil. In the second case, the tsunami waters caused a smaller tank to float. Once the waters receded the tank fell back on the ground, thereby breaking an attached pipe. The spill was aggravated because at the time the tsunami slammed into the refinery, a valve on the tank was open as per normal operating procedure because tank filling was underway. The tank contents continued to be released with a total of 3900 kL spilled.
Figure 2.7 Hydrocarbon Releases From Damaged Pipelines at Sendai Refinery due to Tsunami Impact © Google.
In the eastern part of the refinery, several atmospheric tank roofs vibrated during the earthquake which caused a number of minor spills that stayed, however, confined to the roofs. In addition, although the processing area was not damaged by the tsunami, the earthquake caused some pipe movement and damage and consequently some minor oil spills.
In the Sendai City area of the refinery, the tsunami caused a tanker ship to crash into the pier which resulted in pipeline damage, but no spill occurred. In the Shiogama City area of the refinery, upon hearing the tsunami alarm the workers disconnected the ships which set sail for the open sea.
While the emergency responders knew that there was a fire at the refinery 5 h after ignition due to smoke coming from the facility, they had no means of accessing the site as the debris created by the tsunami had basically obliterated the access roads. Some flyovers with helicopter provided by the Japanese army were made to assess the extent of the fire. Firefighting on land only started on Mar. 15 when an access road was made. The emergency responders had to bring the fire-fighting equipment into the refinery by hand, as a gasoline pipeline that had been moved inland by the tsunami, blocked the gate and had spilled. The on-site equipment could not be used due to tsunami damage.
The fire fighters had to use heavy breathing apparatus to enter the refinery. A significant amount of asphalt was released, as well as sulfur. Some sulfur went underground and continued to burn there. The fire fighters had to drill holes in the ground to be able to inject water to quench the burning sulfur. Mobile pumps were set up at four locations in the western section to pump up river water. Foam was also used but it kept being blown away by the wind. Once the refinery could be accessed there continued to be concern due to the radiation danger from the nuclear accident at the Fukushima Daiichi nuclear power plant. An order was issued according to which all emergency-response activities at the refinery had to stop if radiation levels reached 0.3 μSv. Fortunately, the maximum measured radiation levels did not exceed 0.12 μSv. The fires at the refinery were extinguished after 5 days.
2.3.2.2. Consequences
At the refinery four people were killed by the tsunami. After ignition of the sulfur and the formation of a toxic gas cloud, the mayor issued an evacuation order for a 2-km radius. This also delayed the intervention of the fire fighters. At a park near the refinery, trees and grass were covered with thick oil from the accident. No detailed information on environmental impacts from the accident is available.
Information on economic losses due to the earthquake and tsunami is limited. The refinery owner reported losses of $US 1.2 billion for the Japanese fiscal year 2010. These losses were due to restoration costs, extinguishment of assets, and running cost. The company estimated another $US 300 million losses due to fixed costs during suspended operations for fiscal year 2011. The refinery returned back to full operations in Mar. 2012.
2.3.2.3. Lessons Learned
The widespread damage and fires in the refinery showed that Natech preparedness levels were low and that emergency-response plans did not adequately consider the consequences of tsunami-triggered Natech scenarios. During reconstruction of the damaged and destroyed refinery parts, the owner addressed some of the critical issues identified during the accident. On the one hand, an artificial hill of 5-m height was raised in the eastern part of the refinery to safeguard emergency-response equipment and teams and from which to coordinate response activities in case of a tsunami. On the other hand, the truck (un)loading facility was moved northeast and farther away from the river for better tsunami protection. This followed the realization that it would be more cost-effective to move equipment or facilities out of harm’s way as retrofitting or hardening of the facility would have been difficult to achieve.
From an emergency-response point of view it was noted that the communications flow during the crisis needed to be improved to provide for faster response in situations where telephones are inoperable and access roads to hazardous installations are destroyed or blocked by debris from the tsunami.
2.4. San Jacinto River Flood, 1994, United States
In Oct. 1994, heavy rainfall in the wake of Hurricane Rosa caused serious flooding in the San Jacinto River flood plain, which at the time of the floods was crossed by 69 pipelines operated by 30 different companies. The floods caused significant pipeline damage and spills, which due to their magnitude raised concerns about health impacts and environmental pollution, as well as preparedness levels of operators. The accident description in this section is based on the investigation report of the US National Transportation Safety Board (NTSB, 1996).
2.4.1. Accident Sequence and Emergency Response
During the flooding in the San Jacinto River basin a total of eight hydrocarbon pipelines ruptured, releasing LPG, gasoline, crude oil, diesel fuel, and natural gas. The diameters of the affected pipes ranged from 8 to 40 in. Another 29 pipelines were undermined, and in some cases the length of undermining approached or even exceeded the length of unsupported pipe considered safe for continued operation. Pipe failures and undermining occurred both at river crossings and new channels in the flood plain.
Analyses of the failed pipes showed fatigue cracks from multiple origins that were created when the pipelines were uncovered and undermined. This exposed them to the floodwaters which oscillated and deflected them. The forces acting on the pipes caused the pipe walls to bend and buckle, thereby creating fatigue cracks that continued to grow until the pipes could no longer contain the internal pressure created by the hydrocarbons they transported.
The ruptured pipelines continued spewing hydrocarbons into the fast-flowing floodwaters, and petroleum products pooled in areas where the water flow was slow. Gasoline from a 40-in. pipeline carried downriver on the water surface ignited, causing several explosions and fires that began moving southward.
Operator response to the pipeline failures varied significantly although the failures were very similar. Some operators shut down operations but left valves open and hydrocarbons in the pipes while others closed valves and purged the pipeline of product. Other operators continued operations in spite of several pipeline failures they were aware of. It was reported that 24 mainline valves near the river were inaccessible because they were submerged by the flood. The Coast Guard managed the cleanup from the federal side. This involved the laying of booms downstream of the pipeline ruptures to protect sensitive areas. The booms also deflected the liquids to narrow areas where they were collected with skimmers or vacuum trucks. A portion of the released hydrocarbons were burned in situ, although there is some controversy regarding the decision considering that the water levels had dropped and the liquids could have been removed by mechanical means.
2.4.2. Consequences
In some areas, an evacuation order to residents was issued because of strong fumes from petroleum products in the river. All persons within 9 miles of a failed 40-in. gasoline pipeline were evacuated. Once the situation was considered under control, flood evacuees returning to their houses were advised to stay indoors until the air quality had improved. Overall, the pipeline ruptures and the subsequent fires caused 545 injuries in residential areas primarily due to smoke and vapor inhalation. Two residents suffered burns, one of which serious. It was fortunate that much of the area had already been evacuated due to the flooding prior to the Natech accidents. Two pipeline workers sustained injuries when removing their company’s damaged pipe. The petroleum fires also caused significant damage to residential and commercial buildings, as well as to cars and boats.
During the floods almost 36,000 barrels of crude oil and petroleum products were released into the San Jacinto River, and 7 billion cubic feet of natural gas were lost. Spill response costs exceeded $US 7 million while losses due to property damage amounted to about $US 16 million (in 1994 $US).
2.4.3. Lessons Learned
The investigation into the pipeline failures during the flood highlighted a number of critical issues related to pipeline design, siting, and operator preparedness. The US National Transportation Safety Board concluded that the most severe damage or ruptures of pipelines occurred in those areas where the river exhibited maximum stream meandering, where sand-mining operations had taken place, and where the river width was constricted due to human constructions which facilitated riverbed scouring. Furthermore, it was found that the design bases of most pipelines that failed or were undermined had not benefitted from an analysis of the dangers that floods could pose to pipeline integrity. With no regulations, industry standards, or guidance available on how to address the hazards of pipeline siting in flood-prone areas, the Safety Board called for the establishment of standards for pipeline design across flood plains or at river crossings.
The Safety Board also criticized the fact that most pipeline operators continued operations in the San Jacinto River valley without assessing the capability of the pipeline design to resist the flood hazard. Also, only few operators took effective response actions to minimize the potential loss of product. It is believed that the failure of the US Department of Transport’s Research and Special Programs Administration (RSPA) to require an operator plan with concrete actions to be implemented in case of floods might have contributed to the severity of the Natech accidents.
Another critical issue identified by the Safety Board concerned the lack of effective operational monitoring to promptly identify the location of ruptures and the absence of remote-controlled or automatic valves. This has led to the release of large volumes of hydrocarbons. The Safety Board called upon the RSPA to establish requirements for valves and leak-detection systems in pipelines.
2.5. Hurricanes Katrina and Rita, 2005, United States
Hurricanes Katrina and Rita impacted the Gulf of Mexico (GoM) in the United States within a short period of time. Hurricane Katrina made landfall, at the upper end of Category 3 intensity with estimated maximum sustained winds of 110 kt, in Southern Louisiana at 11:10 UTC on Aug. 29, 2005 (Knabb et al., 2006a). Less than a month later, while the region was still trying to recover from the impact of Katrina, Hurricane Rita made landfall as an upper Category 3 storm at 07:40 UTC on Sep. 24, 2005, with an estimated intensity of 100 kt, in extreme southwestern Louisiana (Knabb et al., 2006b). Several levees separating Lake Pontchartrain and the city of New Orleans were breached, resulting in the flooding of about 80% of the city. Hurricane Katrina is responsible directly and indirectly for at least 1833 deaths making it one of the deadliest hurricanes in US history (Knabb et al. 2006b).
Combined, the two hurricanes triggered hundreds of hazardous-materials releases from onshore and offshore oil and gas installations. Sengul et al. (2012) reported over 800 releases in 2005 and 400 releases in 2006 due to the hurricane impacts. Guidry (2006) notes that the volume of onshore and offshore oil spills from the two hurricanes was 30.2 million liters. The hazardous-materials releases and oil spills represented an additional burden on emergency responders and remaining residents, and affected the supply of fuel needed for emergency-response purposes (Cruz and Krausmann, 2009). Although the storms impacted onshore installations as well as offshore infrastructure, the impacts on the offshore oil and gas industry were unprecedented. Thus, in the next section, a summary of the impacts on the offshore industry is presented.
2.5.1. Accident Sequence and Emergency Response
Over 4,000 offshore platforms and more than 50,000 km of pipeline were exposed to the storms (MMS, 2006). Cruz and Krausmann (2009) identified over 611 releases directly attributed to offshore oil and gas platforms and pipelines due to both hurricanes (reported up to May 2006). Table 2.1 presents a summary of the reported hazardous-materials releases from offshore platforms and pipelines due to Hurricanes Katrina and Rita.
Table 2.1
Hazmat Releases From Offshore Facilities and Pipelines due to Hurricanes Katrina and Rita
| Hurricane Katrina | Hurricane Rita | Total | |
| Platform | 366 | 162 | 528 |
| Pipeline | 42 | 40 | 83 |
| Unknown | 0 | 1 | 1 |
| Total | 408 | 203 | 611 |
Adapted from Cruz and Krausmann (2009).
Table 2.1 shows that the releases from offshore infrastructure during Hurricane Katrina doubled those reported for Hurricane Rita, with about 80% of the releases occurring from destroyed or damaged platforms and rigs. The large number of releases from platforms was attributed to higher exposure of platforms to the storm forces including hurricane winds, wave action, and currents (Cruz and Krausmann, 2009). There were, however, over 450 offshore pipeline breaks, indicating that pipelines were vulnerable, too. The common practice to deinventory pipelines in preparation for an approaching hurricane helps explain the lower number of oil and gas spills from pipelines in spite of the many storm-induced breaks. The main types of substances released were crude oil and other types of oil (e.g., fuel, lubricating, hydraulic) during Hurricane Katrina, and crude oil and natural gas during Rita. A small number of releases of NOx were also reported. However, in a large number of cases the types and quantities of material released were not reported or were unknown. Cruz and Krausmann (2009) found that the number of crude oil and other oil releases during Hurricane Katrina was almost three times higher than during Hurricane Rita, although there were twice as many natural-gas releases attributed to Hurricane Rita.
Damage to offshore platforms and pipelines due to the high winds, wave loading, and strong currents were the main cause of the oil and gas spills (Fig. 2.8). The majority (about 88%) of releases during Hurricane Katrina occurred in the front right quadrant, within a 120-km radius from the storm’s center as it approached land. This is the area that typically experiences the highest wind speeds. Storm surge was also the highest in this area according to the US National Weather Service (Simpson and Riehl, 1981). The higher number of hazmat releases during Katrina may be attributed to the higher wind speeds during Katrina as compared to Rita as it approached land.
Figure 2.8 Oil Rig Washed Aground by Hurricane Katrina Photo credit: LtCdr. M. Moran, NOAA Corps, NMAO/OAC.
There were also a large number of oil spills reported in the near-shore, including spills from Meraux, LA (Murphy Oil Corporation) in the metropolitan area of New Orleans, as well as coastal areas at the mouth of the Mississippi River at Empire (Chevron Oil), Pilot Town (Shell Oil), and Cox Bay (Bass Enterprises Production Company) (Pine, 2006).
The emergency response and cleanup following the hurricanes was difficult given the scale of damage induced by the hurricanes offshore but also onshore across Louisiana, Mississippi, and Alabama. The extensive damage and flooding meant that damaged facilities and offshore oil infrastructure was practically inaccessible. Hurricane Katrina in particular rendered many roads impassable for weeks or even months. Furthermore, communication and electrical power systems were damaged, in some areas for several months. This resulted in limited or no access to fuel for emergency- and repair vehicles. Furthermore, there was limited personnel available because employees had evacuated outside of the impacted areas before the storms, or due to the extensive flooding which resulted in no place to provide boarding and lodging for workers, cleanup crews, and first responders. Delays in providing emergency response and cleanup occurred due to overwhelmed support resources, such as boats and other vessels, diving equipment, etc. Cruz and Krausmann (2009) reported that by May 2006 only in about 30% of the cases had some remedial action been taken at the time the releases were reported.
A multiagency (including local, regional, and federal agencies) Incident Command Post (ICP) was set up at the US Coast Guard offices in Baton Rouge. The ICP coordinated and prioritized sites for cleanup in order to minimize public health threats and environmental impacts (ICP, personal communication). Cleanup efforts in the coastal marshes were implemented through the use of boats and barges. Coastal cleanup methods included use of in-situ burn techniques, which involved fewer response resources and had proven to be one of the best environmental removal methods for reducing impacts to the sensitive coastal marsh (Pine, 2006).
2.5.2. Consequences
The hurricanes completely shut down oil and gas production, importation, refining, and distribution in the Gulf of Mexico for days or even weeks. In addition, the two storms together caused extensive damage offshore including destroying or damaging 276 platforms, 24 rigs, and 457 pipelines (Cruz and Krausmann, 2008). There were no reported human casualties from offshore infrastructure due to the storms’ impacts. The combined extended downtimes, economic losses from the damaged infrastructure, cost of lost products, and environmental clean up resulted in unprecedented losses to the oil and gas industry. This caused a hike in oil prices around the globe in the weeks that followed the storms.
The environmental consequences of the oil and gas spills are less well understood and were even considered low in the direct aftermath of the storms (Koehler, 2007; Pardue et al., 2005). Leahy (2005), however, warned that only time would be able to tell what the true consequences on the coastal ecosystems, and the fisheries and tourism industries might be. Many of the spills affected the immediate area around the location of the spill, or were washed over the coastal wetlands and marshes. In some cases, spilled oil was dispersed by wave action and storm surge. Pine (2006) reports that both the short- and long-term impacts of these oil releases on ecosystems along the many miles of coastline were and will continue to be examined by the teams from NOAA’s Office of Response and Restoration. According to Pine (2006), the teams monitor shallow near-shore and wetland environments in areas impacted by chemical releases in an effort to characterize the magnitude and extent of coastal contamination and ecological effects resulting from this storm.
2.5.3. Lessons Learned
Hurricanes Katrina and Rita together triggered a number of hazardous-materials releases from offshore oil and gas platforms and pipelines that was far greater than that reported for previous storms. A high percentage of hazmat releases occurred not more than 50 km from the coastline where storm-surge values were higher and where most platforms, rigs, and pipelines were destroyed or damaged.
The lower number of releases from pipelines demonstrates the effectiveness of the pipeline deinventory practice prior to the storms. On the other hand, the high number of hazardous-materials releases from platforms was attributed to the destruction or damage of the platform by wind or wave action, which resulted in the discharge of oil and other dangerous substances processed or stored on board. Even in cases where the structural integrity of the platforms was untouched, wave action caused inundation of decks and possibly tipping over of storage tanks and containers holding hazardous materials. A lack of more detailed information on the root causes of failures leading to the releases makes it difficult to make precise recommendations on possible improvements in terms of anchoring mechanisms, flood proofing, etc. Cruz and Krausmann (2009) recommended improvements in damage investigation and reporting in order to facilitate an in-depth analysis of the damage and hazmat release dynamics and hence to prevent the recurrence of future releases.
Even one year later, hazardous-materials releases caused by the storms were still being reported, and only about 30% of the releases had been cleaned up or were under some remedial action. This fact indicates that improvements were needed concerning poststorm damage and release assessment, and prestorm planning for poststorm emergency response and clean up.
2.6. Milford Haven Thunderstorm, 1994, United Kingdom
The case study descriptions in the previous sections are examples of major Natech accidents that can typically accompany natural disasters. However, also natural hazards commonly not considered a serious threat, such as lightning, rain, or freeze, can trigger Natech events with often severe consequences. The following is an example of a major accident in a refinery that was initiated by a thunderstorm. The accident description is based on the investigation report of the UK Health and Safety Executive (HSE, 1997).
2.6.1. Accident Sequence and Emergency Response
The refinery located in Milford Haven was constructed in 1964 and it is one of the largest refineries in Western Europe. It produces gasoline, diesel fuel, kerosene, liquefied petroleum gas (commercial propane and butane), and petrochemical feedstocks with a throughput capacity of 270,000 b/d, including 220,000 b/d of crude oil and 50,000 b/d of other feedstocks, and a storage capacity of 10.5 million barrels. Over the years, significant upgrades to the installation have allowed the plant to increase its production capacity.
The accident on Jul. 24, 1994 involved the refinery’s crude distillation unit (CDU), the fluidized catalytic cracking unit (FCCU), and its flare system. The crude oil was separated in the CDU by fractional distillation into naphtha and gas, kerosene, light and heavy diesel, and vacuum gas oil (VGO). The VGO provided the feed for the vacuum distillation unit which in turn fed the FCCU.
The first accident sequence was initiated when a thunderstorm passed over the refinery between 7:20 and 9:00 a.m. Lightning strikes caused a 0.4 s power loss and subsequent power dips throughout the refinery. This caused the repeated tripping of pumps and coolers and consequently led to the lifting of the crude column pressure safety valves. As a consequence, flammable vapors were released and ignited by a lightning strike. The CDU was shut down as a result of the fire.
The power dips caused by the thunderstorm also initiated the second accident sequence which some 5 h later resulted in a powerful explosion and fires. The HSE investigation concluded that a combination of failures in management, equipment, and control systems led to the actual release of hazardous substances and eventually to the explosion. Due to process upsets caused by the power dips, the FCCU briefly lost and then regained VGO feed between 7:47 and 8:00 a.m., leading to feed level fluctuations. The process upset was exacerbated by additional power interruptions at 8:27 and 8:29 a.m. This, together with valve problems that were not recognized, eventually caused the FCCU’s wet gas compressor to shut down, resulting in a large vapor load on the FCC’s flare system. This led to a high liquid level in the flare knockout drum, thereby exceeding its design capacity and forcing the liquid hydrocarbon into the drum’s outlet line which was, however, not designed to take liquid and ruptured due to mechanical shock at an elbow bend (Fig. 2.9). As a result of the rupture at the flare drum’s outlet line a pulsing leak appeared, releasing about 20 t of flammable hydrocarbons. The released hydrocarbon liquid and vapor mixture reached explosive levels and drifted inside the process area. The hydrocarbon cloud was eventually ignited by a heater and an explosion occurred 30 s after the outlet line break at a distance of about 110 m from the flare drum. After the explosion, several isolated fires continued to burn within the process area, most importantly a major fire at the flare drum outlet itself.
Figure 2.9 The Failed Elbow Bend at the 30-in. Flare Drum Outline Line From Which the Hydrocarbons Were Released From HSE (1997). © Crown Copyright
In response to the accident, the fires were contained and an escalation of the accident was prevented by cooling the nearby vessels containing flammable substances. The explosion and fires incapacitated two of the plant’s three flare systems, and consequently plant personnel shut down and isolated the process equipment. Considering that the explosion had disabled the flare relief system, the fires were allowed to burn until the hydrocarbons were exhausted 2.5 days after the explosion. The accident was mitigated by the on-site and county fire-fighting teams. After much deliberation, only the on-site emergency plan was activated although it did not consider the possibility of a fire burning for more than 24 h.
2.6.2. Consequences
The accident resulted in 26 nonserious injuries on site. According to the accident investigation report, a disaster was averted because the accident occurred on a weekend when less employees were on site, and because the alkylation unit adjacent to the FCCU withstood the explosion unscathed. This is testimony to the high safety standards that the unit was built and operated to.
Large areas of the refinery suffered severe structural damage due to the explosion and the fires on-site. The blast from the explosion caused damage to buildings, vessels, columns, tanks, pipework, and pipe racks (Fig. 2.10). Block wall buildings near the blast location were completely destroyed. Interestingly, the control room suffered some internal damage because the door had been open at the time of the explosion. Staff had opened the door as the earlier power interruptions had disabled the air conditioning control. The accident did not cause any community disruption as off-site damage was limited due to the refinery’s location away from population centers. In Milford Haven town, located at about 3 km from the refinery, some properties sustained glass damage.
As a result of the accident, approximately 10% of the United Kingdom’s refining capacity in 1994 was lost during the refinery’s downtime (4.5 months). According to Marsh (2003) the monetary losses due to business interruption amount to US$ 70,500,000. Costs related to property damage, debris removal, and cleanup were estimated at US$ 77,500,000 (both numbers refer to 1994 monetary value).
2.6.3. Lessons Learned
While the initiating event of the accident was the process upset caused by the electrical storm, the direct causes of and contributing factors to the explosion were several:
• In the FCCU the debutanizer valve was stuck closed, a fact unknown to the operators. This led to hydrocarbon liquid being continuously pumped into a process vessel that had its outlet closed. Consequently, once the vessel was full, the hydrocarbons entered the pressure relief system and the flare line.
• The operators were overwhelmed by too many alarms triggered by the process upset, and the display screen configuration of the operator control system made it difficult to identify the cause of the incident. It was concluded that the operators were not adequately trained to handle a sustained process upset.
• Tests on instruments whose incorrect behavior contributed to the accident revealed maintenance issues. In addition, the flare drum’s outline line was known to be corroded and modifications on the drum’s pump-out system resulted in a reduced liquid handling capacity. However, no recorded safety assessment of this modification was available.
Based on these insights, the HSE formulated recommendations for future accident prevention and mitigation in those areas where deficiencies were identified. Most importantly, these concerned a formal and controlled Hazard and Operability (HAZOP) Study in case of modifications; training for staff to better handle unplanned events and perform well under high-stress conditions; and reconfiguration of alarms to facilitate the distinction between safety-critical and other operational alarms. In view of the possibility of prolonged fires, the HSE also recommended considering the availability of adequate supplies of fire-fighting water.
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