Chapter 13
Reducing Natech Risk: Structural Measures
A.M. Cruz*
E. Krausmann**
N. Kato†
Abstract
Structural prevention and mitigation measures can help prevent damage and hazardous-materials releases at industrial facilities, and contribute to reducing their consequences if releases do occur. This chapter introduces a selection of available structural protection measures for different types of natural hazards.
Keywords
risk reduction
structural measure
protection
safety goal
prevention
mitigation
Structural prevention and mitigation measures can help prevent damage and hazardous-materials releases at industrial facilities, and contribute to reducing their consequences if releases do occur. This chapter introduces a selection of available structural protection measures for different types of natural hazards.
13.1. Introduction
Releases of hazardous materials from damaged process or storage equipment pose a substantial threat to human health and the environment. Often, industrial facilities that handle hazardous materials are located in urbanized areas subject to natural-hazard events. In these cases, a Natech event can endanger not only plant personnel, but also residents of the neighboring community. The danger of releases in highly urbanized areas has been explicitly recognized by many developed and developing countries (OECD, 2012).
Limiting industrial development in areas prone to natural hazards is the most efficient way to minimize the danger associated with the potential natural-hazard impact. However, land-use-planning restrictions for existing installations are often very costly and difficult to implement. In this case, supplementary measures are required to protect hazardous facilities. There are various ways in which the risk of Natech accidents can be reduced, including through structural risk-reduction measures, that is, using engineering solutions, as well as through organizational measures. Furthermore, these can be divided into:
• prevention measures—actions or measures that are put in place to reduce the likelihood of damage and occurrence of a hazardous-materials release and
• mitigation measures—actions or measures that are put in place to reduce the impact of hazardous-materials releases if they do occur.
In the following sections we discuss passive and dynamic structural accident prevention and mitigation measures for different types of industrial equipment and building structures, and for different types of natural-hazard events.
13.2. Prevention Measures
13.2.1. Earthquakes
In areas of high seismic risk, large earthquakes (Mw 7.0 or greater) pose one of the greatest threats to industrial plants and other infrastructures housing hazardous materials. The examples described in previous chapters highlight that concrete buildings, steel storage tanks, open steel structures, and other equipment present at industrial facilities are vulnerable to earthquake loads. Steel storage tanks are generally classified as anchored or unanchored depending on the restraint provided to the ground. Unanchored storage tanks may be subjected to uplifting and/or sliding motion with the subsequent tearing of connected pipes in case of strong ground motions (Salzano et al., 2003). Welds in steel tanks are sensitive to corrosion and can lead to wide cracks during earthquake events, particularly in the shell/roof and shell/base-plate joint zones. Liquid sloshing in full (or nearly full) steel storage tanks can result in large axial compressive stresses of the tank shell, causing elephant-foot buckling due to the seismic overturning forces. Sloshing of the liquid near the free surface can damage the roof and upper shell of the tanks (Ballantyne and Crouse, 1997; Salzano et al., 2003; Hosseinzadeh and Valaee, 2006).
Damage or collapse of buildings at adjacent structures at process plants can also cause hazardous-materials releases, major process upsets, or even human casualties (Fig. 13.1). Moreover, industrial installations are a combination of buildings and warehouses, industrial equipment, and lifeline systems, such as plumbing, electrical, heating, ventilation, and air-conditioning systems. An earthquake can damage one or a combination of these infrastructures, thereby causing failures in other parts of the facility through these interconnected systems (Cruz, 2014). In fact, often chemical accidents occur not necessarily because of the earthquake itself but due to the secondary effects of the earthquake, such as power outages, loss of water supply (e.g., collapse of water cooling towers, damage to water pipes), lack of process air, damage of critical equipment (e.g., inoperability of boilers), or failure of standard prevention and mitigation measures.
Figure 13.1 Pipes Collapsed Onto a Building at a Fertilizer Plant During the 2008 Wenchuan Earthquake in China Photo credit: E. Krausmann.
With earthquakes remaining unpredictable despite advances in the natural and engineering sciences, the adoption of appropriate seismic building codes for new plant structures and the retrofitting of older facilities to comply with the latest design codes can help minimize loss of life and property. Building structures related to the operation and administration of a plant or as part of the plant infrastructure (e.g., control rooms, communications, pumping stations, water treatment), or for materials and equipment storage may require special design to ensure that they remain operational following a major disaster.
The impacts of large earthquakes on industrial installations may be severe as the examples of the Kocaeli (cf. Section 2.2) and Wenchuan earthquakes (Krausmann et al., 2010) demonstrated. Lessons from past earthquakes suggest that industrial facilities that adopted earthquake design codes or implemented retrofitting generally performed better (even in earthquakes exceeding design loads) than facilities that had not embraced seismic design. The example of the Great East Japan earthquake in Japan in 2011 (cf. Section 2.3), demonstrated the effectiveness of earthquake prevention measures in Japan through performance-based earthquake design as relatively little damage of major severity occurred due to the earthquake.
Different countries use different seismic building codes. For example, the United States leaves the decision of which building code to adopt to each State, although seismic requirements for new and existing federal buildings exist. The State of California adopted the 2016 California Building Standards Code, which is based on the International Building Code (IBC, 2015). As was mentioned in Chapter 4, chemical accident prevention is regulated in California by the CalARP program. CalARP updated its Guidance for Seismic Assessment in Dec. 2013 (CalARP, 2013), which specifically requires the assessment of:
1. Regulated processes as defined by CalARP Program regulations.
2. Adjacent facilities whose structural failure or excessive displacement could result in the significant release of regulated substances.
3. Onsite utility systems and emergency systems which would be required to operate following an earthquake for emergency reaction or to maintain the facility in a safe condition (e.g., emergency power, leak detectors, pressure relief valves, etc.).
Most importantly, the seismic assessment guidelines provide several performance criteria that apply to individual equipment items, structures, and systems (e.g., power, water, etc.). These criteria may include one or more of the following:
• maintain structural integrity,
• maintain position,
• maintain containment of material, and
• function immediately following an earthquake.
Japan follows the Building Standard (BS) Law revised in 1981 and the Act for Promoting Earthquake Proof Retrofitting of Buildings enacted in 1995 following the Kobe earthquake (Cruz and Okada, 2008). It is generally agreed that engineered buildings in Japan are designed for greater strength and stiffness than similar buildings in the United States and tend to be more resilient (Whittaker et al., 1998). One important aspect of the revised BS law is that it uses performance-based standards where the building is required to satisfy performance criteria with respect to materials, equipment, and structural methods (Japan External Trade Organization, 2005). As explained in Chapter 4, the seismic code was modified to account for lessons learned from the Great East Japan Earthquake in 2011. Furthermore, in Mar. 2016 the Institute for Disaster Mitigation of Industrial Complexes at Waseda University in Tokyo published Guidelines for Earthquake Risk Management at Industrial Parks (IDMIC, 2016). The Guidelines are similar to the CalARP seismic guidance document emphasizing various performance levels, addressing soil problems and structural design issues, as well as prevention and mitigation measures. It differs from the CalARP in that the Japanese guidelines are meant for area-wide assessment at industrial agglomerated areas.
13.2.1.1. Storage Tanks
Storage tanks may be directly damaged by both short- and long-period earthquake ground motions. Typical failure modes of storage tanks during past earthquakes include shell buckling, roof damage, anchorage failure, tank-support system failure, foundation failure, hydrodynamic pressure failure, connected pipe failure, and manhole failure (ALA, 2001; Salzano et al., 2003). Storage tanks may suffer damage due to earthquake-induced liquid sloshing and soil liquefaction. Liquid sloshing and the resulting dynamic loading on the tank wall need to be taken into account in the design of storage tanks in earthquake-prone areas. During the Great East Japan earthquake most storage tanks performed well except along the northwest Japan Sea coast and the Tokyo Bay area, which experienced long-period strong ground motions. This caused liquid sloshing of oil in storage tanks with resultant sinking of floating roofs and other damage, such as failure of pontoons (Zama et al., 2012).
The earthquake prevention measures adopted should consider the tank’s intended use, size, structure type, materials, design lifetime, location, and environment in order to assure life safety and to maintain their essential functions following an earthquake. The Architectural Institute of Japan, which published the 10th edition of “Design Recommendation for Storage Tanks and Their Supports With Emphasis on Seismic Design” (AIJ, 2010), noted that the trend in recent years has been for larger storage tanks, and as such the seismic design for these larger tanks has become more important to guarantee public safety and environmental protection. In addition to the seismic design of the tank structure and foundation, the appropriate Japanese codes (e.g., Fire Safety Code) and standards (e.g., API Standard 650 for welded steel oil storage tanks) should be followed.
Anchoring of above-ground storage tanks can prevent horizontal sliding, tank uplifting, and tank overturning. Anchor and anchor-chair design must be considered carefully to avoid damage between anchor chair and tank shell due to excessive rigidity of anchors (Sakai et al., 1990). Furthermore, some industry guidelines, such as the Process Industry Practice (PIP, 2005) Guidelines for Tank Foundation Designs, do not recommend the use of anchors on large cylindrical storage tanks. Bakhshi and Hassanikhah (2008) studied the performance of anchored and unanchored storage tanks during the Kobe earthquake in 1995 and found that the main differences are related to uplifting phenomena. The authors found that tall and medium storage tanks are more sensitive to anchorage conditions than larger, broader storage tanks.
Damage to tank flanges and connected pipes can be reduced by the use of flexible pipe coupling and flexible pipes as shown in Fig. 13.2.
Figure 13.2 Flexible Pipe Coupling (A) and Flexible Steel Pipe (B) on Large Oil Tanks (20 × 40 m) Photo credit: A.M. Cruz.
Damage of support legs of spherical storage tanks during the Great East Japan earthquake demonstrated the need for improved design and strengthening of leg braces. Furthermore, the need to consider situations where the equipment may be under higher stresses than those experienced during normal operation, e.g., during equipment maintenance and checks, need to be reviewed, and factored into the design of these storage tanks if needed.
13.2.1.2. Pipework and Pipelines
With respect to overland transport pipelines, the cheapest and most effective way to protect the pipeline and its network components (pump/metering stations, valve sites, terminal/tank farms) is adequate siting to keep the vulnerable equipment away from earthquake-prone areas. As this may not always be possible, the risk of accidents in such situations can be significantly reduced by the careful selection of pipeline routes, the line pipe’s orientation with respect to fault lines, and hazard-aware choices for the siting of critical components of the pipeline network (Yokel and Mathey, 1992).
In addition to sensible siting, design safety is the most important pipeline protection mechanism. It relies on the availability and implementation of modern design standards, and it includes the use of resistant pipe materials and novel techniques for the strengthening of joints to better resist seismic loading. In areas of permanent ground deformation induced by liquefaction or at fault crossings, additional measures are required to effectively protect a pipeline. Adjusting the orientation of the line pipe with respect to the fault direction or using low-density backfill material at the trench are common practices in such situations (Girgin and Krausmann, 2015; STREST, 2014).
The Trans-Alaska oil pipeline is an excellent example of how engineering solutions can successfully protect pipelines from even severe seismic activity. The Trans-Alaska pipeline dates back to the 1970s when it was built according to stringent earthquake design specifications to accommodate the possibility of a M = 8 earthquake from the Denali Fault which the pipeline crosses. The implemented earthquake design was put to the test in Nov. 2002 when the fault ruptured during a M = 7.9 earthquake. The strong shaking forces damaged a number of the pipeline’s supports near the fault area, but the pipeline easily accommodated the 4.3-m horizontal and 0.8-m vertical shift at the fault crossing without breaking (USGS, 2003). Having been aware of the possibility of strong earthquakes in the area, pipeline designers had given the line pipe Teflon shoes with which it could slide on long horizontal beams, thereby allowing the pipe to move and giving it flexibility under seismic stress (Fig. 13.3). The overall cost of implementing this measure [about 3 million US$ (in 1970 US$)] was considered significantly below the potential economic losses due to lost revenue and repair costs, as well as environmental cleanup, had the pipeline ruptured.
Figure 13.3 Engineered Seismic Protection Measures Implemented for the Trans-Alaska Pipeline at the Denali Fault Crossing Adapted from USGS (2003), Courtesy of the US Geological Survey.
In case an earthquake occurs, quick operator action might be necessary, such as reducing the flow in the pipeline or shutting it down completely to reduce the stresses on the pipeline wall. In this context, Griesser et al. (2004) discuss the installation of strong-motion detectors on pipelines in seismic areas. Based on the information provided by these detectors, control signals can be issued to support quick shutdown or other types of preventive action.
13.2.2. Tsunami and Coastal Storm Surge
Buildings, storage tanks, and pipelines located in coastal areas subject to tsunami hazards may be vulnerable to wave impact and flooding. Site conditions in the run-up zone will determine the depth of tsunami inundation, water flow velocities, the presence of breaking wave or bore conditions, debris load, and warning time, and can vary greatly from site to site (NTHMP, 2001). The vulnerability of buildings to tsunami loads will depend on several factors including number of floors, the presence of open ground floors with movable objects, building materials, age and design, and building surroundings, such as the presence of barriers (Dominey-Howes and Papathoma, 2007).
The National Tsunami Hazard Mitigation Program (NTHMP, 2001, 2013) in the United States recommends four basic techniques that can be applied to buildings and other infrastructure to reduce tsunami risk, including:
• Avoiding development in inundation areas: This is the most effective prevention strategy but not always possible particularly for existing buildings.
• Slowing techniques: These include the use of specially designed forests, ditches, slopes, and berms which can slow and drain debris from waves.
• Steering techniques: These are used to guide tsunamis away from vulnerable structures and people by placing structures, walls, and ditches and using paved surfaces that create a low-friction path for water to follow.
• Blocking water forces: This technique consists in building hardened structures, such as break walls and other rigid construction that can block the force of the waves.
Until recently, there were no tsunami-specific building codes. Structural design to protect buildings in tsunami-prone regions is generally based on loading due to riverine floods and storm waves, providing little guidance for loads specifically induced by tsunami effects on coastal structures (Yeh et al., 2005). Recently, a new chapter on “Tsunami Loads and Effects” for the 2016 edition of the American Society of Civil Engineer’s ASCE 7-16 Standard “Minimum design loads and associated criteria for buildings and other structures” was introduced in the United States. According to Chock (2015), the ASCE 7-16 Tsunami Loads and Effects chapter will become the first of its kind in the United States for use in the states of Alaska, Washington, Oregon, California, and Hawaii. Chock (2015) explains that the new ASCE 7 provisions implement a unified set of analysis and design methodologies that are consistent with probabilistic hazard analysis, tsunami physics, and structural target reliability analysis. The approach developed results in the first unification of tsunami hazard mapping for design and reflects a modern approach of performance-based engineering.
In Europe there has been an effort at the European Community level, through the Tsunami Risk and Strategies for the European Region (TRANSFER) project, cofunded under the European Union 6th Framework Programme, to improve the knowledge of tsunami processes and risks in tsunami-prone regions particularly in areas, such as Southern Italy, Southern Spain, and Greece. Efforts have centered on modeling hazards, hazard mapping, and vulnerability assessment of critical and essential infrastructure systems [see, e.g., Cruz et al. (2009) for a study on tsunami impact at a refinery in the south of Italy]. One of the key goals of the project was the development of strategies and policies to manage, mitigate, and deal with risks stemming from future tsunami hazards.
13.2.2.1. Storage Tanks
Storage tanks are vulnerable to tsunami loads. Ibata et al. (2013) report that damage to many cylindrical oil storage tanks during the Great East Japan earthquake and tsunami occurred due to sliding, floating, overturning, steel wall buckling, and collapse due to the forces of the tsunami. Fig. 13.4 gives an overview of the various failure modes of tanks under tsunami loading, while Fig. 13.5 presents photos of two tanks damaged by the Great East Japan tsunami. Of the 167 tanks reported damaged, 120 tanks had capacities of less than 500 kL. There was no damage to tanks with capacities larger than 10,000 kL, but the pipework for 27 of these tanks was affected. Slowing, steering, and blocking water techniques may be used for storage-tank protection. Their structural design and heights should be carefully evaluated based on a tsunami-hazard assessment. During the Great East Japan tsunami, earthen dikes around storage tanks at a refinery in Sendai were overtopped. Although the tanks did not float off their foundation, debris impacts caused damage to connected pipes resulting in oil releases. Since the earthquake and tsunami, the earthen dikes have been reconstructed and their height increased. Fig. 13.6 shows the reconstruction of a damaged earthen dike at the refinery in Sendai, Japan.
Figure 13.4 Failure Modes Observed During the Great East Japan Tsunami in 2011 Adapted from Ibata et al. (2013).
Figure 13.5 Examples of Damage to Oil Storage Tanks in Miyagi Prefecture During the Great East Japan Tsunami in 2011 Photo credit: C. Scawthorn.
Figure 13.6 Reconstruction of an Earthen Dike at a Refinery in Japan After the 2011 Tohoku Earthquake Photo credit: A.M. Cruz.
Submersion and subsequent buoyancy are of particular concern for storage tanks that may float off their foundations, thereby tearing pipe connections and resulting in the release of possibly flammable and/or toxic materials. According to Ibata et al. (2013) damage to storage tanks in the Great East Japan tsunami increased with inundation depth higher than 3 m. The authors reported that for inundation depths between 3 and 5 m damage to attached piping and tank body were documented. At inundation depths of over 5 m, most of the storage tanks were damaged.
Research is ongoing to improve the protection of storage tanks during tsunami. Examples include the development of a method to reduce damage by tsunami through design and the application of flexible pipes to reduce tsunami flow loads (Okubayashi et al., 2016; Tar et al., 2016), and tsunami impact minimization based on storage tank distribution.
13.2.2.2. Pipework and Pipelines
Pipework and pipelines are vulnerable to direct tsunami impact and debris loads, as well as hydrostatic and buoyancy loads which may result in pipes floating off and breaking. Overland pipelines were especially vulnerable to tsunami debris impact during the Great East Japan tsunami resulting in several oil spills (Ibata et al., 2013). Commonly used guidelines suggest that a pipe should not suffer any displacement from wave action with a 5-year return period but can experience minor displacement from wave action with a 50-year return period. Major displacement is possible for wave loading with a 100-year return period, but nevertheless the pipe should never collapse. Submerged pipes or pipes near the coastline in tsunami-prone areas should be anchored or braced, and have ballast weights to avoid flotation. Support structures should take into account tsunami wave scouring and soil erosion, or soil liquefaction. Furthermore, lessons from the Great East Japan tsunami showed the need to protect pipelines from debris impact.
13.2.2.3. Other
In addition to implementing equipment-specific structural protection measures, the tsunami risk to hazardous installations in coastal areas can be reduced by lowering the impact forces of tsunami waves. This can be achieved by putting into place offshore breakwalls or other types of barriers onshore (Ergin and Balas, 2006; Jayappa, 2008; Maheshwari et al., 2005). These physical barriers could also keep tsunami-driven debris from washing into the plant. In locations where a facility is not protected by external tsunami barriers, it is advisable to take measures to avoid wave-load damage and water intrusion for all structures containing hazardous substances and all systems that are critical for the safety of the installation (Cruz et al., 2011).
13.2.3. Floods
Flood loads are similar to tsunami loads and include hydrostatic, buoyant, hydrodynamic, and breaking-wave forces, as well as impact loading which results from floating debris (Yeh et al., 2005). Buildings located in river basins and near large water bodies may be subject to flood loads. Similar to tsunamis, flood protection measures include avoiding building in flood-prone areas, particularly within the 100-year flood plain, water proofing of buildings, and slowing, steering, and blocking techniques. Elevation of buildings or important building components above the 100-year flood contour level can protect building functionality and contents. The United States Army Corps of Engineers (USACE) has done extensive work in flood mitigation and control. The report “Flood proofing techniques, programs, and references,” prepared by the USACE, presents a comprehensive review of flood-proofing techniques (USACE, 1997).
Most wealthier nations (e.g., the United States, Germany, Italy, Spain, France) as well as many developing countries (e.g., Mexico, Colombia) limit or prohibit development in the 100-year flood plain. However, the law generally applies to new construction. Thus, existing buildings located within the 100-year flood plains may not be sufficiently protected. Furthermore, political pressure and corruption sometimes result in concession of building permits or illegal development in flood-prone areas (Sierra, 2005; Santander, 2010).
In Japan, the Ministry of Land, Infrastructure and Transport established the comprehensive Flood Control Measures, which consolidate the combined use of facilities to maintain the water-retaining and retarding functions of river basins, the creation of incentives to use land safely and to build flood-resistant buildings, and the establishment of warning and evacuation systems for both tsunami and riverine flooding. Development in high flood-risk areas (within the 100-year flood plain) is regulated through land-use planning controls and flood plain zoning. In addition, the Building Standard law provides provisions for flood proofing of engineered structures, including construction of seawalls and other barriers to protect port terminal facilities from flooding, storm surge, and tsunami waves (Cruz and Okada, 2008).
13.2.3.1. Storage Tanks
Postaccident analyses showed that storage tanks are particularly vulnerable to flood impact. The main damage and failure mechanisms are buoyancy, water drag, and debris impact (cf. Section 3.5). Adequate anchoring with bolts or other types of restraining systems should effectively prevent tanks and other equipment from floating off their foundations under most flood or storm-surge conditions. Another risk-reduction measure is the filling of empty tanks with water in preparation for a flood situation to avoid tank floating and subsequent displacement. This measure is, however, controversial as product residues might still be in the tank, and safety procedures are required to avoid contamination or reaction of the water with the product. Consequently, the implementation of these procedures requires some lead time and, therefore, reliable early warning. Instead of water, a specified amount of product could be left in the tanks at all times, thereby increasing its weight and decreasing the risk of buoyancy. However, should the tank fail, the consequences could be more severe (Krausmann et al., 2011).
Storage tanks are commonly surrounded by containment dikes or concrete walls which retain accidental releases from the tanks. While these catch basins are not designed to keep the floodwaters out, they can provide some protection provided that they are not overtopped or that erosion from the flooding has not compromised the structural integrity of the dikes.
The risk of debris impacts on vulnerable equipment and the associated hazardous-materials releases can be controlled by creating barriers that steer the floodwaters away from an industrial plant. External barriers, such as earthen berms, sheet pile, or concrete walls, can contribute to keep flood-driven debris from washing into a facility (Cruz and Krausmann, 2013).
13.2.3.2. Pipework and Pipelines
There are various standards or codes to ensure that pipelines are able to withstand anticipated external pressures and loads that will be imposed on the pipelines after installation. Furthermore, most codes will provide guidance on the number of shutoff valves to be installed at intervals ranging from somewhere between 5 and 30 km, depending on the population density or presence of sensitive areas along the route of the pipeline. Pipelines should be protected from floods and flash floods that may result in pipe displacement or cause the pipe to sustain abnormal loads. Pipelines installed in a navigable river, stream, or harbor should be buried and have a minimum cover of soil or consolidated rock (NTSB, 1996). Most importantly, a detailed flood risk assessment should accompany any pipeline design to ensure that the maximum flood-hazard risks have been considered in the design, installation, management, and monitoring of the pipeline.
13.2.3.3. Other
Water intrusion in hazardous or auxiliary equipment can cause short circuits or power loss which could trigger or exacerbate a major accident. Similar to tsunamis, also in the case of floods or storm surge, safety-critical systems in a hazardous installation need to be protected from wave-load damage and water intrusion to guarantee their continued functioning. This can be achieved by waterproofing of vulnerable equipment and systems. The implementation of safe equipment design that makes use of, for example, interlocks, fail-open or fail-closed valves contributes toward ensuring safe emergency shutdown in situations in which onsite power is lost due to flooding (Krausmann et al., 2011).
It has been observed during past Natech accidents that waste oil in a plant’s drainage system can be lifted by the floodwaters and be dispersed after stratification on the water surface. Upon contact with an ignition source, which can be a hot plant unit or a lightning strike, major fires and/or explosions can be sparked (Cruz et al., 2001). In areas prone to flooding, including those where a rise in groundwater level is common during periods of long, sustained rainfall, the drainage systems for waste flammable substances and surface run-off water should be segregated.
13.2.4. High Winds
Buildings, storage tanks, and other structures may be subject to wind damage, particularly storm-induced winds, hurricane winds, and tornadoes. Engineering design codes are used to insure that buildings and structures are constructed to withstand particular wind speeds depending on the characteristics of each region. In the United States, the American Society of Civil Engineers (ASCE) provides guidelines for the design and calculation of wind loads in the design standard ASCE 7-05 “Minimum Design Loads for Buildings and Other Structures” (ASCE, 2006). ASCE 7 requires design for the 50-year wind speed with an importance factor for critical infrastructures and industrial facilities containing hazardous materials. This results in the equivalent of a 500-year wind speed for these structures (Steinberg, 2004).
It is important to note that very often wind damage to buildings is due to failure of roofing materials, doors, and windows. These failures, which are often less expensive to prevent or mitigate, lead to weather penetration and damage (Heaney et al., 2000).
In Japan, wind loads are addressed using a performance-based approach. The requirements for building structures in areas subject to high winds in Japan are given by the Wind Load Provisions of the Building Standard law and Building Control System (Cruz and Okada, 2008). These requirements are classified into three categories: life safety, damage prevention, and continuous normal operation. Each of these categories assumes a specific level of load/forces (Hiraishi et al., 1998). Critical facilities and essential building structures will require that they remain operational after being exposed to high wind loads.
13.2.4.1. Storage Tanks
Wind loads on storage tanks include wind pressure on vertical projected areas of cylindrical surfaces and uplift pressures on horizontal projected areas of conical or curved surfaces and roofs. The recently updated design standard ASCE 7-16, “Minimum Design Loads and Associated Criteria for Buildings and Other Structures” provides guidelines for the design and calculation of wind loads on storage tanks (ASCE, 2016).
13.2.5. Lightning
Lightning is a common accident trigger in processing and storage activities (Krausmann and Baranzini, 2012; Rasmussen, 1995). With climate change and the predicted increase in the frequency of severe hydrometeorological hazards, lightning hazards are expected to become more pronounced in the future (IPCC, 2007).
The main purpose of lightning protection is to keep lightning away from flammable and explosive substances, and avoid sparking and flashovers, as well as overheating in conductors. Bouquegneau (2007) emphasizes that in the oil and gas industry, lightning protection systems of class I or even I+ should be adopted in sensitive areas to ensure high safety levels. A number of common protection measures and systems, such as grounding of equipment, lightning rods, or circuit breakers, are available. It has, however, been found that these measures may not prevent equipment damage or failure and the ignition of flammable substances effectively (Renni et al., 2010; Goethals et al., 2008; EPA, 1997). Moreover, lightning protection measures and systems require regular inspections and maintenance as they tend to deteriorate due to chemical corrosion, weather-related effects, and mechanical damage. Protection measures in poor conditions are not effective in preventing an accident.
13.2.5.1. Storage Tanks
Lightning is a frequent source of fires in storage tanks containing flammable substances (Renni et al., 2010; Chang and Lin, 2006). The rim seal of atmospheric floating-roof tanks has been identified as the most likely point of ignition during a lightning strike. Regular checks of the rim seal and maintaining it in good condition will limit the escaping of flammable vapors and hence the risk of ignition during a lightning storm.
The International Standard on protection against lightning (IEC, 2006) indicates that tanks are essentially self-protecting provided they are continuous metallic containers with a minimum shell thickness that depends on the metal the tank is made of (e.g., 4 mm for steel tanks). Additional protection measures might be required for instrumentation and electric systems associated with the operation of these tanks. Bouquegneau (2007) notes that measures for lightning protection should be taken in accordance with the type of tank. Isolated tanks and containers should be earthed at least every 20 m.
The situation is somewhat different for floating-roof tanks containing flammable substances. For more effective lightning protection, the roof should be bonded to the tank shell, and tank seals and shunts that safely conduct stray currents to the ground should be designed with the objective to minimize the risk of ignition. This includes the determination of the optimum number of tank shunts and their location. For floating roof tanks, multiple shunt connections at 1.5-m intervals around the roof perimeter are recommended (Bouquegneau, 2007). Interestingly, in some cases tank shunts have been found to actually increase the risk of fires during lightning storms, as they are a source of sparking when hit by lightning (LEC, 2006).
Currently, no consolidated methodology is available for analyzing the risk of lightning impacts at hazardous installations. However, first attempts in this direction have been made by developing a quantitative methodology for determining the lightning capture frequency of hazardous equipment and the associated damage potential (Necci et al., 2014, 2013). These studies also discussed the benefits of selected types of lightning protection systems and how their positioning onsite can influence risk-reduction efforts.
13.2.5.2. Pipework and Pipelines
The International Standard on protection against lightning also defines protection measures for overland transport pipelines. For instance, it recommends that above-ground metal pipelines should be earthed every 30 m (IEC, 2006). For pipeline stations, surge-protection devices should be implemented to prevent disturbances in control systems. Cathodic protection systems, implemented to reduce the risk of pipe corrosion by establishing a pipe-ground voltage differential, are generally safeguarded against surges and lightning currents. Several incidents suggest, however, that lightning can overcome this system which causes concern as to the effectiveness of corrosion protection.
13.2.5.3. Other
Lightning can cause onsite power blackouts and power dips which can upset processes, affect electrically operated safety systems, and as a consequence lead to loss of containment. It is crucial to identify the dangerous conditions which can result from a power loss to be able to prioritize the processes that should receive emergency power from internal backup systems. It should also be considered to shut down highly hazardous processes under these conditions, blow-down pressurized equipment, and put process units into safe mode. During the starting-up of the installation in the wake of a lightning storm, processes need to be monitored carefully to detect possible malfunctions that could threaten plant safety, as early as possible (Krausmann et al., 2011).
13.3. Mitigation Measures
The design and implementation of mitigation measures to reduce the impact of hazardous-materials releases concurrent with natural disasters requires a careful risk assessment to make certain that these remain functional or operational following a natural disaster. Typical mitigation measures include containment walls/dikes around storage tanks to contain any liquid release and to limit the spill surface area for vaporization in case of volatile substance, the installation of oil-spill detectors and automated emergency shutoff valves to decrease spill quantities, water cannons and foaming systems with in situ and easily accessible (e.g., next to each tank) foam stocks to insulate the spill surface and prevent vaporization, water curtains to wash out toxic gas releases, water sprinkler systems around and over the storage tanks for fighting fires and to cool off tanks in the case of fire in nearby area (Fig. 13.7), fire walls to protect control rooms or other sensitive areas (e.g., residential areas), a sufficient number of fire hydrants, above-ground water pipelines with pumps and inlets for external water feed to reduce the risk of pipe breaks due to ground displacement, and high-capacity backup power generators in the case of power outages, etc. (Girgin, 2011; Steinberg and Cruz, 2004). The effectiveness of the existing protection measures should be tested periodically to ensure that they function properly during natural-hazard conditions. Wherever possible, multiple mitigation measures should be implemented to prevent the escalation of the accident.
Figure 13.7 Retrofitting of a Storage Tank Affected by the 1999 Kocaeli Earthquake in Turkey With a Sophisticated Sprinkler System Photo credit: S. Girgin.
Unfortunately, natural hazards are still commonly overlooked in the design of engineered protection measures and systems at hazardous facilities. Damage to safety and mitigation measures can render them inoperable and hence unable to perform their functions (Fig. 13.8). Past earthquakes have shown that containment dikes may fail during strong ground motion (Steinberg and Cruz, 2004; Ibata et al., 2013). The use of liners inside containment dikes or walls to prevent leakage in case of tank rupture and dike/wall break will provide added protection. Nevertheless, during the Great East Japan earthquake, soil liquefaction and large ground displacement caused damage to dike walls as well as dike liners (Ibata et al., 2013). Thus, seismic design should also be applied to containment dikes/walls. Moreover, all critical active and passive safety barriers (e.g., water curtains/deluges, containment dikes, retention walls) in a hazardous installation need to be designed to withstand the forces of relevant natural-hazard loads (e.g., from earthquakes, tsunamis, floods, etc.). The use of automatic shutdown systems activated by sensors in the wake of natural-hazard loading may prevent releases if plant units have been damaged during a natural event.
Figure 13.8 Damaged Retention Wall During the 2008 Wenchuan Earthquake Photo credit: A.M. Cruz.
Damage to utilities is a generally occurring and major problem during natural hazards. Although emergency- and backup systems for electricity and water supply are usually available at large plants, they might be inadequate to meet the high demand in case of simultaneous multiple Natech accidents. Backup power generators designed not only to maintain lighting, but sufficiently powerful for the operation of critical equipment and/or other plant operations should be considered and planned for.
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