Chapter 3
Lessons Learned From Natech Events
E. Krausmann*
Abstract
Efforts have been launched to systematically collect and analyze information on the causes and dynamics of Natech accidents, as well as of near misses, to support scenario development and the design of better risk-mitigation options. Using postaccident analysis, conclusions can be drawn on the most common damage and failure modes and hazmat release paths, particularly vulnerable storage and process equipment types, and the hazardous materials most commonly involved in these types of accidents. This chapter gives an overview of natural-hazard specific lessons learned and also discusses features common to Natech accidents triggered by different natural hazards.
Keywords
postaccident analysis
damage mode
equipment vulnerability
loss of containment
cascading effect
lesson learned
Efforts have been launched to systematically collect and analyze information on the causes and dynamics of Natech accidents, as well as of near misses, to support scenario development and the design of better risk-mitigation options. Using postaccident analysis, conclusions can be drawn on the most common damage and failure modes and hazmat release paths, particularly vulnerable storage and process equipment types, and the hazardous materials most commonly involved in these types of accidents. This chapter gives an overview of natural-hazard specific lessons learned and also discusses features common to Natech accidents triggered by different natural hazards.
3.1. Data sources and quality
Lessons can be learned in all phases of risk and accident management, from prevention and preparedness to response and recovery. Depending on the scope of the study, there are analyses of single accidents, which produce immediate lessons specific to the event, or analyses of a set of similar accidents from a broader data pool which yield lessons learned that are more widely applicable. The latter type of study facilitates, for example, the identification of commonly occurring causes of accidents involving specific substances or industries, which may not be easily recognizable within a single occurrence. This analysis also lends itself to identifying technical and organizational risk-reduction measures that require improvement or are missing.
Industrial-accident databases are commonly used for retrieving sets of Natech accident case histories for further analysis. These databases contain accident data from the open literature, government authorities, or in-company sources. Examples of such data repositories are the French ARIA database, the European Commission’s Major Accident Reporting System (MARS), The Accident Database of the UK Institution of Chemical Engineers, or the US Coast Guard National Response Center (NRC) database. The quality of information reported in the various industrial-accident databases is not uniform and exhibits different levels of detail and accuracy. This is due to the difficulty of finding qualified information sources, especially in situations where accident reporting by the industry or by authorities is not compulsory, for example, when spill quantities are below reporting thresholds. Data collection has to then rely on voluntary record keeping which is often done by nonexperts. Industrial-accident databases also suffer from a lack of information on near misses, which would be of particular value for learning lessons as they give examples of effective risk-reduction approaches and techniques.
The level of detail is particularly nonuniform for Natech accident data depending on whether the consequences of the Natech event were major or minor, and whether comprehensive information was available for reporting. In addition to the reporting bias toward high-consequence events, industrial-accident databases frequently lack information on the severity of the triggering natural hazard, as well as on failure modes that led to the hazmat release. This makes it difficult to reconstruct the dynamics of the accident and renders the development of equipment vulnerability models linking the natural-hazard severity to the observed damage almost impossible. Consequently, the European Commission has set up the eNATECH database for the systematic collection of Natech accident data and near misses. The database exhibits the more sophisticated accident representation required to capture the characteristics of Natech events and is publicly accessible at http://enatech.jrc.ec.europa.eu.
As yet, most Natech accident analyses concerned accidents triggered by earthquakes, floods, or lightning. Priority was given to these hazards due to the generally greater severity of Natech events caused by earthquakes (Antonioni et al., 2009), and the high frequency of accidents initiated by floods and lightning in the European Union and the OECD (Krausmann and Baranzini, 2012). Systematic analyses of the dynamics and consequences of Natech accidents caused by other natural hazards are scarce.
3.2. General Lessons Learned
Postaccident analyses of a multitude of Natech events caused by specific types of natural hazards soon revealed that there are certain commonalities regardless of the natural-hazard trigger. These studies indicated, for instance, that atmospheric storage tanks, and in particular those with floating roofs, appear to be particularly vulnerable to earthquake, flood, and lightning impact (Krausmann et al., 2011). While no systematic studies for other types of natural hazards are readily available, individual case histories seem to support this conclusion also in case of storms or heavy rain (MAHB, 2014; Bailey and Levitan, 2008; Godoy, 2007).
From an industrial-safety point of view, the high susceptibility of storage tanks to natural-hazard impact is problematic, as these plant units often contain crude oil, gasoline, or other types of flammable liquid hydrocarbons in large quantities. It is therefore not surprising that many Natech accidents involve hydrocarbon releases that often ignite and escalate into major fires or explosions (Table 3.1). With hazmat releases possibly occurring from several sources at the same time, an increased ignition probability coupled with concomitant damage to safety barriers and systems and the frequent loss of lifelines, the likelihood of domino or cascading disasters is also higher for Natech events compared to conventional industrial accidents.
Table 3.1
Substances Involved in a Sample of Flood-Triggered Natech Accidents According to an Analysis by Cozzani et al. (2010)
| Substance Category | Number of Accidents |
| Oil, diesel fuel, gasoline; liquid hydrocarbons | 158 |
| Propane, butane, LPG | 12 |
| Fertilizers | 11 |
| Acid products | 7 |
| Cyanides | 5 |
| Oxides | 5 |
| Ammonia | 5 |
| Chlorine | 3 |
| Explosives | 3 |
| Calcium carbide | 3 |
| Soap and detergents | 1 |
The good news is that risk mitigation generally seems to pay off. Facilities fare better during natural events if they have benefitted from natural-hazard specific design and the implementation of Natech risk-reduction measures (e.g., Cruz et al., 2016; Pawirokromo, 2014; Cruz and Steinberg, 2005; Bureau and Kokkas, 1992; Lopez et al., 1992). Where these measures are inadequate or totally lacking, damage is more severe or even catastrophic. Problem areas that stand out in most Natech accidents are related to insufficient prevention and preparedness, often caused by the lack of structural design features to withstand the natural-hazard loads, the absence of or the weak enforcement of safety regulations, and by a lack of guidance on how to address the problem of Natech risks in the chemical- process industry.
The biggest challenge for the industry and authorities is a change in mindset to accept that Natech hazards can have significant impacts. In-depth analyses of accident data often indicate grossly inadequate design bases of hazardous installations in natural-hazard prone areas due to the use of generic design criteria instead of acknowledging the specific requirements of process equipment under natural-event loading. Ignorance of the need for Natech-specific additional safety measures and a lack of Natech risk assessment contribute to low preparedness levels. Another common risk factor that was identified is the reliance of industry on external lifelines and emergency-response resources for managing a Natech accident rather than preparing a “stand-alone” emergency plan that considers the failure of response systems during a natural disaster. If response resources are overwhelmed the accident can quickly escalate.
3.3. Earthquakes
The postaccident analysis of data sets related to earthquake-triggered Natech events indicates that multiple and simultaneous hazmat releases are particularly common during earthquakes accompanied by an increased risk of cascading events. Damage to industrial facilities due to direct shaking impact or ground deformation induced by soil liquefaction are the main damage and failure modes of structures built in susceptible areas (e.g., Lanzano et al., 2014; Krausmann et al., 2011). From a safety point of view, damage to buildings or equipment that do not contain hazardous materials is of no immediate concern although the associated economic losses can be huge. The predominant damage modes in this category include elephant-foot- or diamond buckling (Fig. 3.1), the stretching or detachment of anchor bolts causing lateral displacement or uplifting of equipment, or the deformation or failure of support columns and other types of foundation structures. The main hazmat-release mechanisms during earthquakes are tank damage with losses from the tank’s roof top due to liquid sloshing, the sinking of floating tank roofs, failure of flanges or rigid tank-pipe connections due to direct shaking impact, or liquefaction-induced ground deformation that leads to pipe ruptures and foundation failures (Lanzano et al., 2015; Krausmann and Cruz, 2013; Zama et al., 2008; 2012; Krausmann et al., 2010). Examples are shown in Figs. 3.2 and 3.3. These releases can be minor or severe. Major releases are caused by tank overturning or collapse due to earthquake loading. Liquid sloshing, for instance, can compromise the structural integrity of tanks which are full or nearly full (Zama et al., 2008, 2012; Salzano et al., 2009; Campedel, 2008).
Figure 3.1 Diamond Buckling of Silos Near the Epicenter of the 2011 Tohoku Earthquake in Japan Photo credit: E. Krausmann.
Figure 3.2 Collapse of a Dryer and Pipe Severing at a Fertilizer Factory Hit by the 2008 Wenchuan Earthquake in China Photo credit: E. Krausmann.
Figure 3.3 Flange Failure at a Fertilizer Plant in the Area Hit by the Wenchuan Earthquake Photo credit: E. Krausmann.
Release modes from chemical containers in warehouses involve the collapse or overturning of storage racks or the toppling and falling of chemical drums or intermediate bulk containers (IBCs). Dynamics analyses support the conclusion that racks loaded with IBCs are more vulnerable to ground motion than those loaded with drums. The analysis also showed that while robust anchorage reduces the likelihood of rack collapse, it also increases the potential for drum or IBC toppling (Arcidiacono et al., 2014).
Accident analyses also showed that flammable hazmat releases are likely to ignite during earthquakes. Floating roof tanks in particular are prone to fire scenarios as liquid sloshing can bounce the tank’s metallic roof against the tank wall, which can create sparks and ignite the tank content. From the statistical analysis of the available accident data set, an ignition probability of 0.76 was calculated by comparing the number of accidents with only release to those with release and ignition (Campedel, 2008). With a reporting bias toward high-consequence events, this number should be considered an upper limit.
3.4. Tsunami
A significant number of industrial installations are located in tsunami-prone areas all over the globe. Nevertheless, quantitative data on tsunami damage to industrial structures is scarce, in particular when compared to damage data related to earthquake impacts. The reason is likely related to the low frequency of large tsunami events, and the very recent (post 2004 Indian Ocean tsunami) efforts to start collecting and analyzing information on industry-specific tsunami impacts.
The tsunami triggered by the 2011 Great East Japan earthquake and the extensive damage and destruction it caused in vast parts of the Japanese industry offers an opportunity to learn important lessons. Post-tsunami analyses identified direct hydrostatic and hydrodynamic forces from water inundation, as well as impact forces from water-borne debris as important damage and hazmat-release mechanisms. The high speeds obtained by the water can also drag large floating objects, such as ships, into a hazardous installation which can significantly aggravate the damage severity. Salzano and Basco (2015) contend that while debris impact can be assessed using impact analysis, the large uncertainties related to the type and number of objects (including ships) transported by the tsunami waters render the assessment difficult.
The tsunami forces caused washing away of equipment foundations, tank and pipe floating and displacement, tank overturning and collapse (Fig. 3.4), and the breaking of pipe connections and ripping off of valves which were often accompanied by the release of significant amounts of hydrocarbons (Krausmann and Cruz, 2013; Nishi, 2012). The sheer force of a strong tsunami would be able to affect a large variety of structures and equipment, however, storage tanks, and in particular atmospheric ones, appear to be especially vulnerable.
Figure 3.4 Destroyed Heavy Oil Tank at a Thermal Power Plant Battered by the Mega Tsunami in the Wake of the 2011 Tohoku Earthquake in Japan Photo credit: A. Kouchiyama.
Damage to industrial facilities was also observed in cases where the tsunami compromised the structural integrity of buildings which then collapsed onto the hazardous equipment housed within. FEMA (2012) attributes structural tsunami damage also to wind forces induced by wave motion and scour and slope/foundation failure.
Like earthquakes, strong tsunamis can have a large impact zone, and multiple releases of different types of hazardous substances are expected to occur at the same time with potentially manifold consequences. In addition to possibly driving debris-laden water into a hazardous installation, tsunamis would also widely disperse flammable spills or toxic releases triggered by a preceding earthquake or by the tsunami itself. The ignition probability is high under these circumstances, as is the resulting risk of large-scale fires and the likelihood of cascading effects with severe secondary consequences. This also raises questions about the risk of medium- to long-term soil contamination, in particular if the released substances are toxic or environmentally persistent (Bird and Grossman, 2011). While no detailed study on the consequences of hazardous-substance releases due to tsunami exists, by analogy with river floods it is likely that some substances would react with the tsunami waters and thereby create other chemical compounds that could be even more toxic or flammable.
3.5. Floods
River floods can affect individual equipment but also entire hazardous installations through buoyancy and drag forces. Flotation of equipment off its foundations due to flooding of catch basins, as well as subsequent displacement due to water drag, can strain or break tank-pipe connections, leading to minor hazmat leaks but also to more severe, continuous releases (Cozzani et al., 2010). This is a particular problem for empty or nearly empty storage tanks in case anchoring is inadequate or completely missing. While an empty tank by itself does not pose a Natech risk, if it starts floating and is displaced it can become a collision hazard for other equipment onsite. If the force of the floodwaters is sufficiently high, it can cause tanks to collapse or implode, thereby releasing the complete inventory of hazardous substances contained in the unit. Water intrusion in electrical equipment and subsequent power failure or short circuits can affect process and storage conditions and indirectly trigger a Natech accident, for example, via loss of cooling and pressure build up in vessels and emergency flaring of hazardous substances.
Another important hazmat release mode is the impact of floating debris dragged along with the floodwaters on sensitive equipment. This is very similar to debris impact during tsunamis, although the water speed is generally lower during river floods. Depending on the flood height and speed, these floating objects can be smaller items, such as branches, cylinders, or barrels, but also cars or vessels which can do a lot of damage to hazardous facilities. Debris is also a major issue for overland pipelines during flood conditions and an important cause of pipe ruptures. At river crossings, flood-induced erosion and scouring of the river bed can uncover buried pipelines and undermine their foundations, leaving them exposed to debris impact and water pressure (Fig. 3.5). In addition, if too much length of pipe is undermined, it might break due to the unsupported weight. An in-depth analysis of hazardous liquid pipeline Natech accidents in the United States indicates that the highest amounts of hazmats were released during pipe ruptures caused by floods as opposed to other types of natural hazards (Girgin and Krausmann, 2015).
Figure 3.5 Exposed Petroleum Pipeline Due to Flooding in Pennsylvania, USA Photo credit: C. Kafer.
Like tsunamis, floods usually affect large areas and can carry released hazardous materials over great distances. Consequently, there is the additional risk of the floodwaters becoming a vector for the dispersion of toxic or flammable substances over wide stretches of land with the associated elevated risk of cascading events (Fig. 3.6). Interestingly, floods can also lift flammable waste from an installation’s sewer system when the drainage of waste and surface water are not segregated. Contact of these substances with hot surfaces or ignition by a lightning strike can cause fires that spread with the floodwaters (Krausmann et al., 2011; Cruz et al., 2001).
Figure 3.6 Hydrocarbon Release at a Refinery During the Coffeyville Floods in the USA in 2007
The flood caused a spill of 90,000 gallons of crude oil that polluted a wide swath of land. Photo credit: Kansas Wing of the Civil Air Patrol.
The flood caused a spill of 90,000 gallons of crude oil that polluted a wide swath of land. Photo credit: Kansas Wing of the Civil Air Patrol.
Depending on the hazardous substances involved in the accident, the consequences can be manifold. Nevertheless, water contamination is the most common outcome of flood-triggered Natech events and can include the pollution of surface and underground water, as well as extensive soil contamination in the inundated areas. The severity of the consequences strongly depends on the amount of substances released, their solubility and density (Cozzani et al., 2010). Ignition of flammable substances stratified on the floodwaters, explosions, and the atmospheric dispersion of toxic materials are also common.
The postaccident analyses also highlighted additional scenarios ordinarily not considered in conventional industrial accidents. Some chemicals react violently with water and create toxic or flammable vapors in the process. This adds to the risks of the primary substance release by creating a secondary hazard to the population and the environment, but also to emergency responders. Examples of such chemicals are calcium carbide which after contact with water forms flammable acetylene, or cyanide salts which react with water to create hydrogen cyanide, a toxic gas (Cozzani et al., 2010).
3.6. Storms
Storms comprise a number of phenomena, each of which can adversely affect the chemical-process industry or hazmat-storage areas. These phenomena can cause damage on-shore via flooding from storm surge, that is, high-speed water driven by gale-force winds, and through wind pressure and wind-driven rain (McIntyre and Ford, 2009; Godoy, 2007; Cruz et al., 2001). Offshore facilities are not only affected by high winds but also by wave loading. Blackburn and Bedient (2010) note that storm surge and wave elevations are significantly underrepresented in the engineering literature.
Although no systematic analyses of storm-triggered Natech accident data exist, damage and failure modes can be deduced from single accidents. Flood impacts due to storm surge or heavy rain associated with storms lead to the same types of damage as for river floods discussed in the previous section. Equipment flotation and displacement due to storm surge and wind, the associated breaking of vessel-pipe connections, short circuits, and power outages can cause small but also major chemical releases (Fig. 3.7). Heavy rain can tip or sink floating tank roofs, thereby exposing the tank contents to the air and making them easily accessible to potential ignition sources, such as lightning. Since storm surge can cause a rise in water levels of canals or rivers connected to the ocean, also installations not sited directly at the coast can be subject to storm-surge effects (Cruz and Krausmann, 2013).
Figure 3.7 The Water and Gale-force Winds Accompanying Hurricane Katrina Floated and Displaced Two Half-Filled Tanks Along the Mississippi River With 3.8 Million Gallons of Oil Pouring From the Tanks Photo credit: Louisiana Department of Environmental Quality.
Wind-related damage includes shell buckling, toppling of process units and tanks, and tank-roof damage (Godoy, 2007; Cruz et al., 2001). Bailey and Levitan (2008) note that larger tanks have a tendency to fail due to inward collapse of the tank shell, in particular if they are nearly empty, while smaller tanks are more prone to shell buckling after being hit by wind-borne debris, or toppling over. Tank roof damage is caused by the uplift forces of strong winds which exceed the weight of the roof plate (Carson, 2011). For fixed roofs this can result in the tearing of roof-to-shell joints, peeling away of the roof plate, and dislodging of the roof structure (Braune, 2006). Fig. 3.8 gives an example of roof destruction during Hurricane Katrina. In the case of floating roofs, the wind pressure can cause water on the roof to shift, thereby creating an unsymmetrical load which may result in the structural failure of the roof.
Figure 3.8 Wind-Induced Destruction of a Fixed Tank Roof at an Oil Refinery During Hurricane Katrina Photo credit: NOAA.
High winds, storm surge, and underwater currents can also affect offshore oil and gas infrastructure causing rig tie-down problems and wave loading on platform decks, the breaking of platform-riser connections, and mooring failure with subsequent loss of station keeping that can set mobile offshore drilling units adrift (Cruz and Krausmann, 2008; Det Norske Veritas, 2007; Energo Engineering, 2007). Anchor dragging of drifting drilling units and submarine landslides can damage the underwater pipeline network and other subsea facilities.
The type of design and filling level determine the susceptibility of equipment to storm surge or wind impact. Minor, moderate, but also major releases of toxic, flammable, or explosive chemicals are possible both on- and offshore (Cruz and Krausmann, 2009; Cruz et al., 2001). These substances disperse in the air, stratify on or dissolve in water, and are carried away by the flood once the catch basin is overtopped by storm surge or rain-related flooding. Like for floods and tsunamis, the presence of water can trigger chemical reactions that generate additional toxic or flammable substances. During storm conditions the control of hazmat releases from hazardous installations is extremely challenging due to potentially widespread storm damage with power outages, disruption of communication, destruction or blocking of access roads, and the absence of workers displaced by a major storm.
3.7. Lightning
Several studies indicate that lightning is one of the most frequent natural-hazard accident triggers in chemical processing and storage activities (Krausmann and Baranzini, 2012; Chang and Lin, 2006; Rasmussen, 1995). In pipeline systems, lightning might be a more important accident initiator than previously thought (Kinsman and Lewis, 2000). It is interesting to note that the effectiveness of commonly implemented lightning protection measures, such as grounding of equipment, lightning rods, or circuit breakers, in preventing fires or damage in industry has proven to be inconclusive (Goethals et al., 2008).
The analysis of lightning-triggered Natech accidents showed that there exist different mechanisms for equipment damage and failure (Renni et al., 2010; ARIA, 2007). Direct structural damage is caused by thermal heating from the lightning strike. This can lead to the puncturing and rupture of tank shells and pipelines. If the lightning energy is not sufficient to pierce the pipe body, it might still disable the pipeline’s cathodic corrosion protection system and cause pitting. This spot can become the source of corrosion and failure months after the lightning strike. Indirect structural damage can occur via the collapse of structural components (e.g., flare stacks) struck by lightning that damage hazardous equipment when falling. Another often underestimated indirect damage mechanism is lightning impact on the power grid, or on electrically operated control and safety systems whose disruption could create process upsets and subsequent hazmat releases, for example, from vent and blow-down systems (Renni et al., 2010). This can turn out to be a particular problem during start-up of a hazardous installation following a thunderstorm.
Flammable vapors are often present at the rim seal of floating roof tanks. If lightning strikes the tank roof or in its vicinity, immediate ignition can occur (Fig. 3.9). The energy carried by lightning can also ignite flammable gaseous releases from other types of equipment or stratified substance spills on the ground. Fires are therefore a frequent consequence of lightning strikes involving flammable substances. In fact, fires and explosions are the most frequent outcome of lightning impact for storage tanks. A statistical analysis of selected accident data yields an ignition probability of 0.82 which is not surprising considering that lightning is an ignition source itself. As for earthquakes, this number is likely an upper limit due to the reporting bias toward high-consequence accidents in industrial accident databases (Krausmann et al., 2011).
Figure 3.9 Lightning-Triggered Fire in a Gasoline Storage Tank in Oklahoma Photo credit: Assistant Chief D. Brasuell (ret.), Bixby (OK) Fire Department; Courtesy of Industrial Fire World Magazine.
The majority of lightning-triggered Natech accidents seem to result in hazmat releases that do not ignite or explode. However, once loss of containment has occurred, the released chemicals can disperse in the air, or cause water and soil contamination. Furthermore, lightning-triggered release quantities can be significant, with almost 40% of the accidents analyzed in Renni et al. (2010) exceeding 1000 kg. Matters are further complicated during lightning storms accompanied by heavy rain which can cause releases from spills in catch basins that overflow or from drainage-water segregation systems whose capacity is exceeded.
3.8. Others
3.8.1. Extreme Temperatures
Recent studies showed that low temperatures were among the top three causes of Natech accidents in the European Union and OECD between 1990 and 2009, together with lightning and floods (Krausmann and Baranzini, 2009, 2012). These studies also found that while cold weather and freeze pose an important threat to hazardous installations, the associated risk is in most cases severely underestimated.
During conditions of extreme or prolonged cold weather with temperatures below zero, or quickly alternating freeze and thaw phases, various types of industrial equipment and their appurtenances are vulnerable to malfunction and damage. This includes pipework (e.g., transfer or drainage lines) that is not adequately insulated or lacks insulation, pumps, valves, and flanges on tanks or pipes, pipe welds and joints, but also control systems and sensors performing safety-relevant functions (ARIA, 2012a; CSB, 2008).
There are different mechanisms by which low temperatures can cause damage in hazardous installations. The freezing of industrial equipment or pipeline network components can lead to component malfunction and leaks, for instance due to valve or control-system failures (e.g., overfilling caused by a frozen level detector). Ice formation in pipes can cause blockage of auxiliary pipes and overpressure which might eventually lead to pipe rupture, or tank overflow if an overflow line is blocked by ice. In the pipeline network the most important cold-weather related damage mode is the expansion of freezing water and subsequent pipe cracking or bursting by mechanical forces. Water naturally present in the transported hazardous substances is the main source of the ice. Another important damage mechanism is frost heave in which a section of the ground is lifted upward due to the freezing of water present in the soil. If a buried pipeline crosses this area, it will be affected by the vertical ground displacement and can buckle. Falling ice and snow can create physical loads on the equipment that could also cause cracks and hazardous-materials releases (Girgin and Krausmann, 2015).
Although severely underestimated as an accident initiator, cold-weather related damage to hazardous equipment is frequent and has caused ground, water, and atmospheric pollution, as well as fires and explosions with sometimes significant emergency-response, cleanup, and restoration costs.
Hot weather can affect hazardous installations in different ways. A recent analysis of heat-related accidents in France concluded that direct exposure to solar radiation and thermal stresses can cause reactive substances to evaporate and self-ignite (ARIA, 2012b, 2015). High temperatures can lead to the decomposition and polymerization of substances, or the formation and accumulation of flammable vapors in confined spaces with an elevated risk of ignition. In pressurized systems, excessive heat can trigger pressure surges with the subsequent actuation of safety valves and leaks of hazardous gases. Auxiliary equipment, such as pumps or compressors, can also be a source of releases and spills if they overheat and break down. In pipeline systems, Girgin and Krausmann (2015) identified heat-induced valve and strainer failures, as well as collar joint failures due to ground shifts brought about by extended drought periods. While pollution and explosions have been observed in relation to hot weather conditions, fires appear to be the predominant outcome.
3.8.2. Volcanoes
There are very few studies related to Natech risks due to volcanic eruptions. Milazzo et al. (2013a,b) and Salzano and Basco (2009) analyzed the danger to industrial facilities around Mt. Etna and Mt. Vesuvius volcanoes in Italy. These areas are characterized by strong seismic activity triggered by the volcanoes, a high population density, and intense industrialization, including large industrial ports.
These studies focused on the potential risks to atmospheric storage tanks due to volcanic ash fallout which is considered to be an important phenomenon potentially affecting large areas by which the integrity of industrial facilities could be compromised. In this context, the main damage and failure mechanisms are an increase in the loading on fixed or floating tank roofs due to ash accumulation, or damage to rubber seals caused by the abrasiveness of the ash. Assessing the resistance of fixed roofs to damage by ash loading, and of floating roofs to sinking or capsizing, Milazzo et al. (2013a) estimated threshold values for ash deposits for both wet and dry conditions. Saturation of volcanic ash with rainwater and the associated increase in density reduce the ash load required to cause damage to atmospheric tank roofs. Overall, the study showed that only extremely large explosive eruptions could damage tank roofs or cause them to sink or capsize. Simple mitigation actions, such as removing the ash by blowing or brushing it from the roof, can be effective.
Another volcano-related phenomenon that can endanger industrial facilities and lead to hazardous-materials releases are lahar flows. Lahars are volcanic mudflows triggered by the melting of ice and snow that while descending the volcano can damage or bury infrastructures in exposed areas. During the 1989/1990 eruptions of Redoubt Volcano in Alaska, lahar flows caused partial flooding of a crude-oil terminal in the Drift River valley. Although no oil was spilled, in the aftermath of the event the operator of the terminal built dikes of 6-m height around almost all the terminal and raised critical electrical equipment to a minimum of 1-m above the ground (Brantley, 1990). The oil terminal was again affected by lahars during Redoubt’s 2009 eruption, but the dikes around the tank farm effectively protected it from a potentially catastrophic inundation and oil spills (Fig. 3.10). Pierson et al. (2014) argue that exclusion dikes can effectively enclose and protect valuable infrastructure from lahar impact.
Figure 3.10 View West of the Oil Terminal in Drift River Valley, Alaska
Lahar deposits have ramped up to the top of the west dike and spilled over in a couple of locations. Water entered the compound along an existing roadway in the foreground. Photo credit: G. McGimsey, AVO/USGS.
Lahar deposits have ramped up to the top of the west dike and spilled over in a couple of locations. Water entered the compound along an existing roadway in the foreground. Photo credit: G. McGimsey, AVO/USGS.
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