Case Studies on the Application of HAZOP Methodology for Loss of Primary Containment (LOPC) Scenarios in Tank Farms

Michael B. Saura, Reyson G. Dela Cruz, and Marian D. Mendoza

Keywords: PHA, HAZOP, safety, tank farm, LOPC, Highly Hazardous Chemicals

Abstract. The Philippines hosts numerous tank farms essential for the storage of chemicals in diverse applications. About 36% of the nation’s total import terminal storage has a combined capacity of approximately 6 million barrels (bbls). These facilities carry high risks due to the flammable, reactive, explosive, and toxic nature of the stored chemicals.

As of 2023, there have been 650 recorded tank farm fire incidents globally, with 10 to 29 fires each year causing numerous injuries and fatalities. These incidents highlight the need for awareness of robust risk assessment methodologies and safety practices. In August 2024, the Philippine National Standard (PNS) for Process Safety Management was published, offering essential guidance on PSM implementation. This includes clauses corresponding to Process Hazard Analysis (PHA), which systematically identifies and analyzes potential hazards in facilities handling highly hazardous chemicals. A PHA methodology, Hazard and Operability Study (HAZOP), can effectively mitigate risks in tank farms with significant Loss of Primary Containment (LOPC) potential.

HAZOP examines deviations, documents consequences, assesses risks and recommends engineered safeguards to mitigate unacceptable risks. This paper demonstrates the importance of HAZOP through a consequence-based analysis of tank scenarios in a petroleum refinery. It covers high-severity consequences for each storage tank handling specific chemicals: (1) large pool fire from a crude tank (50,000 bbls), (2) large flash fire from an asphalt tank (15,000 bbls), (3) overpressure and leak from a propane tank (5,000 bbls), and (4) overpressure and rupture of a butane tank (20,000 bbls).

This study highlights the critical role of HAZOP in enhancing safety in tank farms and the Chemical Process Industry (CPI). It demonstrates the methodology’s ability to prevent incidents and mitigate risks, thereby protecting people, businesses, and the environment. The proponents recommend conducting such analyses, as they are essential for preventing LOPC scenarios and consequences in the CPI, either as a proactive practice or in compliance with regulatory standards and requirements.

Introduction

Tank farms are critical infrastructure in the Philippines, essential for supporting the country’s energy and industrial sectors. These facilities serve as vital storage sites for diverse products, primarily petroleum products, which are stored in stationary bulk tanks above and below ground [1]. Notably, Keppel Infrastructure Trust (KIT) and Metro Pacific Investments Corporation (MPIC) collectively hold a significant portion, accounting for 36% of the nation’s total import terminal storage capacity, equivalent to 6 million barrels (bbl) [2]. This infrastructure is pivotal in driving the country’s economic growth, particularly in densely populated regions such as Metro Manila, central Luzon, and northern Luzon [2].

Despite tank farms’ significant industrial and economic impact, their safety assumptions should not be taken for granted [3]. Tanks store a wide range of substances, often including hazardous chemicals that are flammable, reactive, explosive, and toxic (FRET), posing challenges in preventing loss of primary containment (LOPC) [1]. Tank farms are associated with various risks, such as fire, explosions, spills, toxic releases, adverse environmental conditions, static discharge, and runaway reactions [1, 3]. These incidents often result from inadequate maintenance, insufficient training, inappropriate operational procedures, inadequate control of ignition sources, and poor housekeeping [1].

As of 2023, around 650 tank farm fire incidents occur globally, each year with 10 to 29 causing injuries and fatalities [4]. One notable incident at International Terminals Company, LLC (ITC) on March 17, 2019, involved a fire sparked by a tank’s circulation pump failure, spreading to 14 other tanks and releasing 470,000 to 523,000 barrels of hydrocarbons [5]. Another fire due to a naphtha leak at Marathon Petroleum Refinery in Garyville, Louisiana, on August 25, 2023, was contained by surrounding dykes without casualties [6, 7]. In addition to fires, chemical spills are a significant concern at tank farms. For example, on November 7, 2023, a spill from IMPEX Philippine Company Inc. in Bauan, Batangas, prompted the evacuation of 460 families (1,464 residents) and resulted in two hospitalizations. The spill occurred due to a partially open gate valve in the bund wall, allowing naphtha solvent to flow into the sea [8].

These incidents underscore the need for robust risk assessment methodologies and rigorous safety practices in tank farms. Implementing hazard identification, risk assessments, and sound engineering practices can prevent such incidents. For instance, Process Hazard Analysis (PHA) systematically identifies and analyzes potential hazards in facilities handling hazardous chemicals. In August 2024, the Philippine National Standard (PNS) for Process Safety Management was published, offering essential guidance on PSM implementation. This includes clauses corresponding to PHA, which systematically identifies and analyzes potential hazards in facilities handling highly hazardous chemicals. A PHA methodology, Hazard and Operability Study (HAZOP), can effectively mitigate risks in tank farms with significant Loss of Primary Containment (LOPC) potential.

HAZOP is a systematic qualitative technique for identifying process hazards and potential operational issues. It involves scrutinizing every aspect of a process using specific guide words to detect deviations from the intended design and understand their causes and consequences.

This paper illustrates the significance of HAZOP through a consequence-based analysis of tank scenarios in a petroleum refinery, focusing on high-severity outcomes associated with each storage tank handling specific chemicals. The primary objective of this study is to demonstrate how HAZOP enhances safety in tank farms and the Chemical Process Industry (CPI) by preventing and mitigating risks to safeguard people, businesses, and the environment. This research aims to illustrate the importance of HAZOP to deviating scenarios in tank farms from escalating to LOPC and assess consequences in the CPI, either as a proactive practice or in compliance with regulatory standards and requirements.

The present study focuses on applying the HAZOP methodology to assess and mitigate potential LOPC—scenarios in oil and gas industry tank farms. The scenarios considered in this study include a large pool fire from a crude oil tank, a large flash fire from an asphalt tank, overpressure and leak from a propane tank, and overpressure and rupture of a butane tank. The study particularly emphasizes the need for comprehensive HAZOP studies in tank farms that handle crude oil, bunker oil, asphalt, propane, and butane.

This research is limited explicitly to tank farms dealing with these chemicals, excluding other chemicals tank farm facilities may manage. As a result, while the findings and recommendations presented in this study are highly relevant to tank farms within the petroleum industry, they may need to fully address the unique risks and challenges associated with other varieties of chemicals in tank farms. The study underscores the application of the HAZOP methodology for LOPC scenarios in tank farms to prevent and mitigate the given high-severity scenarios related to the chemicals mentioned.

Literature Review

Process Hazard Analysis (PHA). PHA is a systematic evaluation conducted in chemical and manufacturing plants to review operational procedures methodically. It aims to identify and assess potential causes and consequences of hazardous chemical releases. By analyzing equipment reliability, human actions, and environmental impact, PHA helps organizations identify risks that could harm safety, disrupt operations, or affect the environment. PHA aims to enhance safety measures, facilitate informed decision-making, and implement proactive actions to mitigate risks associated with handling hazardous materials [9, 10].

PHA encompasses assembling a team of experts, identifying hazards, assessing risks, implementing controls, and consistently reviewing and updating the analysis. It is a regulatory requirement in numerous countries for industrial processes that handle hazardous chemicals [10, 11].

As OSHA and other regulatory bodies require, employers must do a PHA for each covered process, emphasizing its importance as part of OSHA’s PSM standard and EPA’s RMP. PHAs must prioritize evaluating the most hazardous processes first, identify and assess risks, and apply controls. To guarantee continued safety and compliance, PHAs must be finished on time and updated at least once every five years [9].

PHA Applications. PHAs are critical in ensuring safety during new process designs by identifying hazards early, managing risks during operational changes, and maintaining ongoing safety through regular reviews to address new hazards and technological modifications [12].

Common PHA Methodologies. Various PHA methodologies are employed to evaluate process hazards effectively. Standard methods include checklists that compare processes using established codes and standards, a “What If” analysis that identifies risks through hypothetical questioning, and a Hazard and Operability Study (HAZOP) focusing on equipment design deviations. Failure Mode and Effect Analysis (FMEA) also assesses the consequences of equipment failures, while Fault-Tree Analysis uses graphical models to identify the root causes of potential accidents [9].

Choosing the suitable PHA methodology depends on factors like the process’s complexity, duration of operation, and whether a previous PHA has been conducted.

Fig. 1. Common PHA Methodologies

Hazard and Operability (HAZOP). HAZOP, a systematic approach applied in chemical, pharmaceutical, oil and gas, and nuclear industries, is essential for assessing risks and operational challenges in complex processes. It is recognized under OSHA’s Process Safety Management (PSM) standard as a PHA methodology. The method aims to identify, evaluate, and mitigate hazards associated with hazardous chemicals, which are critical for preventing severe injuries, property damage, and reputational risks. By examining operational deviations and human factors, HAZOP enables organizations to proactively manage risks during project planning, design phases, and modifications to existing processes [13, 14].

Another objective is ensuring that deviations are promptly recognized and effective control measures are implemented to protect the process. Its structured approach thoroughly evaluates potential deviations from intended operations, facilitating proactive risk mitigation and compliance with regulatory standards [13, 14].

HAZOP Methodology. The HAZOP methodology involves a systematic approach to identifying and mitigating risks in complex processes involving hazardous chemicals. It begins with forming a multidisciplinary team of experts to review Process and Instrumentation Diagrams (P&IDs) and operating procedures, identifying nodes where deviations occur. During a HAZOP session, an interdisciplinary team systematically analyzes a process by selecting specific nodes and using guide words like “More,” “Less,” and “Reverse” to identify potential deviations from the intended operation. The team determines possible causes for each deviation, such as equipment failure or human error, and assesses the resulting top events and their consequences, like fires or explosions. They evaluate existing safeguards and, if necessary, recommend additional controls to mitigate risks. The session concludes with documenting findings and developing a risk management plan, ensuring ongoing safety and compliance through continuous monitoring [13].

HAZOP as the Most Commonly Used PHA Methodology. HAZOP is the most commonly used PHA methodology due to its rigorous and systematic approach, making it highly adaptable across various industries, including petroleum refineries, nuclear facilities, and pharmaceuticals. Its key strengths lie in its ability to foresee and mitigate potential hazards, enhancing overall safety for employees, facilities, and the environment. HAZOP also promotes valuable collaboration and training opportunities, enabling participants to gain fresh perspectives on process evaluation. However, the comprehensive nature of HAZOP requires significant time, multidisciplinary team involvement, and meticulous planning to ensure effective risk assessment and management strategies [15].

Tank Farm Incidents. This section discusses previous studies on tank farm incidents and risk assessments.

Intercontinental Terminals Company (ITC) Tank Farm Fire [5]. On March 17, 2019, a significant tank farm fire occurred at the Intercontinental Terminals Company (ITC) bulk liquid storage terminal in Deer Park, Texas. The fire originated in Tank 80-8, an 80,000-barrel aboveground storage tank containing flammable butane and naphtha. Over three days, the fire spread to 14 surrounding tanks, causing over $150 million in property damage. Additionally, approximately 470,000–523,000 barrels of hydrocarbons, petrochemicals, firefighting foam, and contaminated water were released into Tucker Bayou and Buffalo Bayou due to breaches in containment walls, severely impacting the local ecosystem. This contamination led to the closure of a seven-mile section of the Houston Ship Channel and surrounding parks, disrupting the community and triggering multiple shelter-in-place orders due to elevated benzene levels in the air.

Fig. 2. Aftermath of ITC Tank Farm Fire Incident

The US Chemical Safety Board (CSB) investigation identified several critical factors that exacerbated the incident. The primary cause was the ignition of flammable vapors in Tank 80-8 due to a malfunctioning circulation pump. The severity of the fire was worsened by the absence of remotely operated emergency isolation valves and inadequate gas detection systems, which could have alerted personnel to the hazardous mixture before ignition. Additionally, design deficiencies in the tank farm layout facilitated the spread of the fire. The CSB also noted that regulatory exemptions from Process Safety Management (PSM) standards for atmospheric storage tanks contributed to the incident. The CSB recommended several measures, including establishing a comprehensive process safety management system, installing flammable gas detection systems, and revising the PSM standards to remove exemptions for atmospheric storage tanks.

Caribbean Petroleum Corporation (CAPECO) Tank Terminal Explosion and Multiple Tank Fires [16]. The explosion at Caribbean Petroleum Corporation (CAPECO) in Bayamón, Puerto Rico, on October 23, 2009, serves as a stark example of the catastrophic effects of industrial accidents involving large-scale petroleum storage. The incident occurred when an aboveground storage tank overflowed during the transfer of gasoline from a ship to onshore tanks. The spilled gasoline created a vapor cloud that ignited upon contact with a source at the wastewater treatment facility, resulting in multiple explosions. These explosions severely damaged 17 out of 48 storage tanks, as well as nearby residences, commercial buildings, and military installations. The event lasted nearly 60 hours and also led to significant environmental contamination as oil and firefighting foam leaked into wetlands, soil, and waterways.

Fig. 3. CAPECO Tank Farm Fire Incident

The US Chemical Safety Board (CSB) investigation highlighted numerous deficiencies in CAPECO’s safety procedures and regulatory oversight, which exacerbated the incident’s severity. Key issues included unreliable tank gauging equipment, inadequate tank filling procedures, lack of high-level alarms, and the absence of automatic overfill prevention systems. Additionally, there needed to be more risk assessment requirements, emergency response preparedness, and a general failure to implement industry consensus standards. The CSB also noted that exemptions from OSHA’s Process Safety Management (PSM) standard and the EPA’s Risk Management Plan (RMP) contributed to the need for proper safety measures. The CSB recommended that regulatory bodies and industry organizations, such as the EPA, OSHA, and the National Fire Protection Association (NFPA), implement stricter regulations and improve safety standards to prevent similar incidents in the future.

Buncefield Tank Farm Fire [17]. The Buncefield oil storage depot catastrophe, which occurred on December 11, 2005, in Hertfordshire, England, was a devastating event marked by large-scale explosions and a massive fire. The incident began when a fuel storage tank overflowed, releasing significant amounts of gasoline vapor into the atmosphere. The vapor cloud eventually ignited, leading to multiple explosions and a fire that burned for five days, destroying most of the site. The damage extended to twenty-three storage tanks and nearby buildings, with the overall cost of destruction estimated to exceed £1 billion. The catastrophe severely impacted the surrounding community, causing widespread disruption, closing major highways and rail lines, and necessitating the evacuation of 2,000 people. Despite the extensive damage, there were no fatalities, though 43 people sustained injuries, and the environmental impact was significant, requiring extensive soil and groundwater remediation.

Fig. 4. Buncefield Tank Farm Fire Incident

The Buncefield Major Incident Investigation Board (MIIB) identified several key factors that contributed to the incident, including the failure of the high-level alarm system, inadequate safety management systems, and poor operational procedures. Additionally, the need for adequate containment and drainage systems and regulatory gaps in the storage and handling of hazardous chemicals exacerbated the situation. To prevent similar incidents in the future, the MIIB recommended enhancing the design, installation, and maintenance of high-level alarm systems, strengthening safety management through comprehensive training and operator competence, and updating regulatory frameworks. They also emphasized the need to adopt inherently safer design principles in storage facilities and improve emergency response planning with better coordination between site operators and local authorities.

IMPEX Philippine Company Inc. [8]. On November 7, 2023, a chemical spill in Barangay San Miguel, Bauan, Batangas, caused by IMPEX Philippine Company, led to the evacuation of 468 families (1,464 residents) due to the dangers posed by naphtha, a paint-making chemical. While no serious injuries were reported, two people were hospitalized for breathing difficulties. The spill, caused by a partially opened gate valve, affected approximately 6,000 square meters and resulted in the death of some fish. Although one naphtha drum was lost, 11 drums were later recovered, and the chemical naturally dispersed the following day. The incident caused significant environmental contamination and forced evacuations.

Synthesis

Over the past few years, numerous tank farm incidents involving loss of primary containment (LOPC), fires, or explosions have been attributed to inadequate risk assessments and incomplete hazard analyses of tanks and their components. This issue arises from exemptions that certain tanks or components in tank farms or storage facilities have from undergoing comprehensive risk assessments or formal process safety management. Historically, standards such as OSHA’s PSM and EPA’s RMP lacked coverage for these specific equipment types in tank farms, leading to major accidents like the Buncefield tank farm fire and the CAPECO Tank terminal incident. Consequently, the CSB and MIIB frequently recommend removing these exemptions and mandating comprehensive risk assessments and formal process safety management for tank farms to prevent similar incidents in the future.

A notable instance highlighting the consequences of inadequate process safety management in tank farms is the ITC tank farm fire, where atmospheric storage tanks were exempt from these standards and not covered by OSHA’s PSM or EPA’s RMP. Therefore, the CSB recently recommended to OSHA and EPA that these exemptions for atmospheric storage tanks be eliminated from the PSM standard.

In contrast, until the Philippines published the Philippine National Standard (PNS) for Process Safety Management in August 2024, no specific risk management standards or laws mandating PSM or PHA existed. Most safety practitioners were only familiar with occupational safety and health and had little knowledge of process safety. This gap contributed to incidents like the chemical spills from IMPEX Philippine Company that damaged the coastal area of Bauan, Batangas.

Methodology

This research applies the HAZOP (Hazard and Operability) methodology to analyze high-severity scenarios within tank farms in a petroleum refinery. The study is designed to systematically identify and assess potential Loss of Primary Containment (LOPC) events by selecting cases representing the most common types of LOPC scenarios. The methodology outlined here details the steps taken to conduct a consequence-based HAZOP analysis, the selection criteria for case scenarios, and the documentation process.

The first step in the research methodology involved selecting specific case scenarios from a reference HAZOP worksheet. The selection criteria were based on severity levels, where only scenarios with high severity (Severity A and B) were chosen to ensure the focus remained on scenarios with significant potential impact. Additionally, particular LOPC events that represent the most common types of LOPC scenarios in tank farms were selected. These scenarios were identified as critical due to their potential for severe consequences. Based on this, the following case scenarios were identified:

Large Pool Fire from a Crude Oil Tank. Crude oil is a flammable liquid that is heterogeneously sourced from nature, with its physical and chemical properties varying wildly depending on the location and time of extraction [18]. It is a mixture of liquid hydrocarbons with some nitrogen, sulfur, and oxygen compounds. Paraffin, naphthenes, and aromatics are typical hydrocarbon structures found in crude oil [19]. The American Petroleum Institute, API, classifies crude oils depending on their specific gravity, such as heavy, medium, or light. Its appearance also ranges from colorless to black. Crude oils are classified either as “sweet” or “sour” depending upon the level of sulfur content, wherein sweet crudes have 0.5% or less sulfur by weight and sour crudes have greater than 1% [19].

Light, sweet crudes are prone to ignition due to the high content of flammable vapor and ease of ignition. In the case of an accident, lighter crudes behave more like gasoline, while heavier crudes behave more like diesel fuel. Vapors from spills of volatile liquids are easily ignited and can create an explosive atmosphere; some vapors are heavier than air and may settle into hollows, then spread to ignition sources [20]. Crude oil’s flashpoint, which gives off sufficient vapors to be ignited by an open flame, can range over an extensive temperature. Most new crude oils and diluted bitumen contain many volatile components and may be flammable after a spill, depending on the loss rate of highly volatile parts. Undiluted bitumen and heavy crude oils generally are not flammable [21].

Crude oil is typically stored in large above-ground cylindrical steel tanks, reaching diameters as large as 30 meters and heights of 10 meters [19]. The large volumes of crude oil stored at refineries raise a major potential risk of pool fires in case of spillage or tank failure. The high flammability of the light crude oils, with the potential of massive spills, allows for a scenario of catastrophe with severe consequences [18]. Upon ignition, a large pool of crude oil may give an enormous fire with very high temperatures and radiant heat, quickly spreading from one storage tank to another and causing a sensational outcome to the related storage tanks and structure infrastructure. The massive volume of crude oil in storage enhances the magnitude of these fires and subsequent challenges to firefighting and emergency response [22].

One incident involving a crude oil-related fire near crude oil storage tanks, investigated by the US Chemical Safety and Hazard Investigation Board, occurred on August 12, 2016, at the Sunoco Nederland crude oil terminal. The primary cause of the incident was the contractor’s hot work in welding a pipe segment with residual crude oil. The welding process created a flash fire and explosion from overpressure within the pipe segment that expelled CARBER isolation tools installed as part of the project and residual crude oil from the piping ends and injured seven contractor personnel. Fortunately, the flash fire and explosion were contained at the source, and there were no known off-site impacts, with other damage limited to the immediate area of the incident in question [23].

Large Flash Fire from an Asphalt Tank. Asphalt is valued for its waterproofing, adhesive properties, and plasticity—meaning this material retains shape very well and sticks very effectively to the surface. Its viscosity depends on the temperature—with temperature changes affecting its flow and application [24]. Asphalt shows stability across different climates and resists aging from heat and sunlight. An essential property that makes asphalt safe to handle and be used for other purposes is its high flash point. The high flash point asphalts are less easily ignited, and a flash fire is less likely to occur than with lower flash point materials [25].

Though asphalt is not readily flammable, a flash fire can occur under certain conditions with asphalt. The addition or presence of highly volatile and combustible materials like modifiers or solvents with low flash points can reduce the asphalt mixture’s overall flash point, increasing the ignition risk [26]. In another case, overheating asphalt above recommended temperatures may give off flammable vapors, raising ignition potential if the temperature rises beyond the flash point [27]. Finally, an ignition source, whether in an open flame, sparks, or hot surfaces near heated asphalt, could ignite vapors within their flammable range and result in a flash fire.

One of the significant incidents related to this asphalt tank fire is the explosion and subsequent fire at the Husky Energy Superior Refining Company LLC refinery in Superior, Wisconsin that occurred last April 26, 2018. The primary causes for this incident are explosions from two Fluid Catalytic Cracking unit vessels, which propelled over 100 metal fragments up to 1200 feet from the original location. The missile from the blast caused the second major factor of the accident, which punctured the asphalt tank at the refinery and ignited multiple operating areas at the refinery. About 17,000 barrels of hot asphalt were spilled into the refinery. From the explosion and fire, 36 workers at the refinery and contractors were injured and had to be treated at local hospitals; among these responding individuals, there were actual OSHA recordable injuries of 11 people. In addition, the property damage from the chemical disaster was approximately US$ 550 million [28].

Overpressure and Leak from a Propane Tank. Propane is also an extremely volatile and flammable gas that forms explosive mixtures with air. It has a very low boiling point of -42°C (-44°F) at atmospheric pressure, giving it a high degree of volatility at normal temperatures, and instantly vaporizes into gas. Since propane vapor is heavier than air, it will collect in low-lying areas, significantly increasing its potential for ignition or explosion [29]. It has a much lower autoignition temperature and a wider flammability range than methane (natural gas), making propane undeniably more volatile and potentially dangerous [30].

According to explosion tests, it is a fuel with medium reactivity. At unconfined explosion tests, it produces higher overpressures than methane. In closed vessel tests, propane generates nearly twice the maximum rate of rise in pressure compared to methane. Empirical correlations indicate that propane explosions may produce overpressures as much as 40% greater than natural gas explosions in the same conditions and with a similarly stoichiometric fuel-air mixture. This greater explosion severity has been attributed to a higher expansion ratio for propane burning and a different mass diffusivity, making propane flames more sensitive to turbulence-induced instability [31].

Propane is stored and transported almost invariably as a liquid under pressure [32]. When pressurized storage is released, propane will significantly expand to form flammable vapor, which can later travel considerable distances and find ignition sources to ignite, potentially resulting in fires or explosions. Storage and handling of LPG create major safety issues due to high pressure and volatility, with the potential for possibly dangerous leaks through valves, fittings, and piping. Leakage of ignited fluids can result in either jet fire, pool fire, or a vapor cloud explosion, depending on the leakage rate and conditions of confinement [33].

One of the historical events regarding incidents on propane storage tanks is the explosion at the Herrig Brothers Feather Creek Farm, Albert City, Buena Vista County, Iowa, that occurred on April 19, 1998. In this occurrence or incident, the 18,000-gallon propane tank was on fire due to leakage of the propane under the tank. These produced the potential for a BLEVE, boiling liquid expanding vapor explosion. The blast killed two volunteer firefighters, and seven other emergency response personnel were injured. Several buildings were also blown apart by the blast [34].

Overpressure and Rupture of a Butane Tank. Butane is highly flammable and has explosive mixtures with air within the range of 1.6 to 8.4% by volume. The boiling point is as low as -0.5°C at atmospheric pressure, and it vaporizes readily into a gas at ordinary temperatures [35]. It offers an extensive flammability range, characterized by an LEL of 1.9 percent and UEL of 8.5 percent. Butane is highly sensitive to ignition from heat, sparks, or flame; the vapors can also spread and flashback to an ignition source [36].

High pressures result in highly complex oxidation behavior for butane. Studies on the oxidation of n-butane at 100 bar conditions showed the reaction onset temperatures to be around 550 K under oxidizing conditions and 625 K under reducing conditions. Non-thermal runaway behavior was found with temperature ranges of 600–650 K and 625–675 K for oxidizing and stoichiometric conditions, respectively [37].

It is often stored and shipped as a liquefied gas under pressure; significant hazards are if a tank ruptures from butane. The sudden release of pressurized butane has the potential for catastrophic consequences as its heavier-than-air vapors first spread along the ground and may travel a great distance to find an ignition source, causing a flash fire or explosion. If fire is present, containers may vent or release flammable gas; heated containers may rupture outright; ruptured cylinders may become missiles. Since this liquid butane is at an extremely low temperature, direct contact can lead to frostbite injuries. These risks bring forth the importance of proper safety measures in the handling and storing butane so that personnel and surrounding environments are protected [36].

One of the catastrophic events related to butane storage was the fire and explosions at the Intercontinental Terminals Company ITC storage terminal in Deer Park, Texas, last March 17, 2019. The blaze started near Tank 80-8, an 80,000-barrel above-ground atmospheric storage tank holding a blend of naphtha and butane product—a flammable liquid. It could not be controlled, and it spread to another 14 tanks before being put off on the 20th of March. Fifteen tanks had been destroyed, spilling out 470,000–523,000 barrels of hydrocarbons on waterways, firefighting foam, and contaminated water, eventually reaching the Houston Ship Channel. A seven-mile stretch of the channel and some nearby parks were closed due to disruptions like shelter-in-place orders over concerns with air quality related to benzene. Moreover, it estimated more than $150 million in property damage, thus depicting the enormous environmental and social impacts of the accident [5].

In summary, crude oil, asphalt, propane, and butane all serve essential functions in the petroleum industry but present enormous risks if the safety measures are not strictly observed. Past accidents underline tragic results from the mismanagement of highly hazardous chemicals, clearly underscoring the importance of HAZOP.

In the HAZOP methodology application, the process begins with identifying a critical deviation and analyzing specific causes. The primary event that could result from this deviation is then assessed, along with the potential consequences. Existing safeguards are reviewed for their effectiveness in mitigating the risks. Additional safeguards are recommended to prevent or mitigate the event if deemed insufficient. The environmental impact is also considered.

Discussion

Scenario 1. Large Pool Fire from a Crude Oil Tank.

Fig. 5. Schematic Diagram of Scenario 1

Table 2. HAZOP Worksheet of Scenario 1

In the HAZOP study for the crude storage tank (TK-01), the deviation “High Flow” was identified as a critical scenario with potentially severe consequences. The analysis began by examining the causes of this deviation, specifically focusing on the failure of flow control valves (FV-01/02) and the inadvertent opening of a 4-inch bypass block valve. The guideword “High Flow” led the team to consider situations where excessive flow into TK-01 could occur due to mechanical failures, transmitter malfunctions, or incorrect setpoints.

The primary event resulting from this deviation was the overfilling of TK-01, which could cause crude oil to overflow into the secondary containment. Given the process safety time of approximately 10 hours from the normal operating level, the team recognized that while there was some time to respond, the potential consequences were significant. The overflow could lead to a large pool fire, posing a substantial risk to personnel and the environment.

Existing safeguards were evaluated to mitigate these risks. These included a high-level alarm in the crude storage tank and secondary containment to capture overflow. However, the HAZOP team identified that while these safeguards were crucial, they might need to be revised to prevent a pool fire, especially if the overflow ignites.

The team recommended additional safeguards, such as implementing interlock systems that would automatically close the flow control valves upon detecting high levels in TK-01, thereby preventing further inflow. Regular maintenance and testing of the valves and transmitters were also suggested to reduce the likelihood of valve malfunction or incorrect setpoints. Moreover, enhancing operator training to emphasize the criticality of monitoring tank levels and responding promptly to high-level alarms was deemed necessary.

The potential environmental impact of a minor chemical release was also considered, focusing on preventing contamination within the secondary containment area. Although this consequence was categorized as less severe (Severity D), it underscored the importance of robust containment and environmental protection measures.

Scenario 2. Large Flash Fire from an Asphalt Tank.

Fig. 6. Schematic Diagram of Scenario 2

Table 2. HAZOP Worksheet of Scenario 2

In this HAZOP scenario, the deviation “Misdirected Flow” was analyzed, focusing on the potential gravitation between tanks and the mismanagement of lineups, which could result in HVGO from TK-02 being inadvertently directed into the Asphalt Storage Tank (TK-06). The causes identified included the possibility of an NC (Normally Closed) block valve being inadvertently opened and general mismanagement of lineups between the tanks.

The event of concern was the overpressure of TK-06 due to the unplanned transfer of HVGO into the hot asphalt tanks. This situation could lead to increased flashing of HVGO, resulting in the formation of vapors and a significant rise in pressure within TK-03. The analysis recognized the severe consequences of this scenario, particularly the risk of a large flash fire if the vapors were to ignite. Additionally, the potential for personnel exposure to hazardous concentrations of H2S (up to 250 ppm) was noted, highlighting the severe safety risks.

The existing safeguards were evaluated, including a pressure relief valve on the asphalt storage tank, H2S monitors, and personal protective equipment (PPE) for personnel. While these safeguards were deemed essential for mitigating the immediate risks of overpressure and personnel exposure, the HAZOP team identified that they might need to be revised to prevent the misdirected flow.

To address this, the team recommended several additional measures. First, a more robust valve management system was suggested to prevent inadvertent valve operations. This could include interlocks or electronic control systems that require confirmation before any critical valve is opened. Furthermore, enhancing the lineup management procedure, possibly through the use of automated or semi-automated systems, was recommended to reduce the likelihood of human error.

Regular drills and training focused on responding to overpressure scenarios were also suggested to ensure that personnel are well-prepared to handle such incidents. Maintaining and regularly testing the pressure relief valves was emphasized to ensure their reliability in the event of overpressure.

Finally, the environmental consequences of a potential minor chemical release were considered. Although categorized as less severe, the possibility of environmental contamination reinforced the need for effective secondary containment measures and regular monitoring of tank integrity.

Scenario 3. Overpressure and Leak from a Propane Tank.

Fig. 7. Schematic Diagram of Scenario 3

Table 2. HAZOP Worksheet of Scenario 3

In this HAZOP scenario, the deviation “High Pressure” was analyzed with a focus on the potential overpressure of the Propane Storage Tank (TK-03). The identified cause was the malfunction of PCV-03 (Pressure Control Valve) on the natural gas line from the plant distribution system. The specific concern was that this malfunction could result in the valve being stuck open, leading to an unregulated flow of natural gas at 220 psig into TK-03, rated for a maximum pressure of 130 psig. The analysis highlighted the significant risk of overpressure, potentially up to 200% of the tank’s design pressure. Such a scenario could lead to component failure, causing the release of propane, a highly flammable substance. The resulting consequence would likely be a fire or explosion, severely affecting personnel safety and the surrounding environment.

The existing safeguards included a pressure relief valve to vent excess pressure from the propane storage tank and a high-pressure alarm to alert operators to dangerous pressure buildup. While these safeguards are critical in mitigating the immediate risks of overpressure, the HAZOP team recognized that the potential consequences, including a fire or explosion, were severe enough to warrant additional protective measures.

The team recommended enhancing the reliability of the PCV-03 by implementing more frequent maintenance and testing protocols to ensure it functions correctly under all operating conditions. Additionally, the team suggested installing a secondary pressure control valve as a redundant safeguard to prevent overpressure if PCV-03 were to fail. Training operators to respond swiftly to high-pressure alarms was also emphasized to minimize response time in the event of a malfunction.

The environmental impact of a potential minor chemical release was also considered. Although this consequence was rated with lower severity, the need for adequate containment and rapid response to any leaks was highlighted to prevent environmental contamination.

Scenario 4. Overpressure and Rupture of a Butane Tank.

Fig. 8. Schematic Diagram of Scenario 4

Table 2. HAZOP Worksheet of Scenario 4

In this HAZOP scenario, the deviation “Utility Failure” was analyzed, explicitly focusing on the potential loss of cooling due to a failure in the glycol system. The identified causes included the loss of glycol flow due to mechanical issues or human error, such as inadvertently closing a 3-inch block valve on the glycol line. This scenario was of particular concern because it could lead to a significant rise in temperature in the Normal Butane Cooler (E-0004), causing the rundown temperature of butane to increase from 60°F to approximately 180°F.

The analysis indicated that this temperature rise could result in the vaporization of butane within the Butane Storage Tank (TK-04), which has a Maximum Allowable Working Pressure (MAWP) of 30 psig. The potential increase in pressure was estimated to reach up to 140 psig, representing an overpressure of 4.67 times the MAWP, which could lead to catastrophic vessel overpressure and rupture.

The consequence of this scenario was identified as severe, with the potential for a large-scale fire or explosion and significant personnel exposure. The overpressure could result in the release of butane, a highly flammable substance, creating a high-risk environment for both personnel and the facility.

The existing safeguards were evaluated, including high-temperature and high-pressure alarms on the butane storage tank and a pressure relief valve designed to vent excess pressure. While these safeguards are crucial, the HAZOP team recognized that the severity of the potential consequences warranted additional measures.

The team recommended enhancing the reliability of the glycol cooling system by implementing regular maintenance and inspection protocols to ensure it operates correctly. Additionally, an automated shutdown system be installed to stop the inflow of butane to TK-04 if a loss of cooling is detected. This would prevent further heating and vaporization of the butane.

The team also advised on the importance of operator training to recognize and respond promptly to utility failures and abnormal temperature increases. In particular, the procedures for operating and maintaining the glycol system were reviewed to minimize the risk of human error, such as inadvertently closing the block valve on the glycol line.

From an environmental perspective, the potential for a moderate onsite chemical release was considered. The focus was on ensuring that the site had robust containment measures and emergency response plans, which would help mitigate the impact of any release on the surrounding environment.

Summary

Overall, the HAZOP methodology effectively identified the risks associated with each deviation for each specific piece of equipment. The resulting recommendations aimed to strengthen the safeguards to prevent the top event, reduce the likelihood of the safety consequences, and mitigate potential environmental impacts.

Strict safety measures like those used in HAZOP approaches have significant implications for tank farms and the Chemical Process Industries (CPI). Because tank farms handle large hazardous materials such as chemicals and petroleum products, they are prone to various dangers, including fires, explosions, and leaks. Implementing effective safety protocols based on HAZOP studies can immediately result in operational resilience and safety culture in the tank farm.

HAZOP strengthens the plant against catastrophic events resulting in damage to property, environmental pollution, harm to workers, or risks to surrounding communities. In addition, HAZOP helps to bridge procedural gaps, human errors, and process deviations, making it possible to strengthen defenses and ensure compliance with industry standards and regulations. Hence, tank farms that have integrated this kind of safety measure demonstrate their commitment to best practices in risk management and improve their reputation among other members of CPI. Consequently, trust is built among regulators and stakeholders.

Furthermore, including HAZOP-driven safety protocols into day-to-day activities improves productivity while avoiding avoidable incidents that may cause downtime, thereby safeguarding profitability and ensuring business continuity.

Conclusion and Recommendation

This study underscores the critical importance of applying the Hazard and Operability (HAZOP) methodology in managing and mitigating risks associated with Loss of Primary Containment (LOPC) scenarios in petroleum-based chemical tank farms. The case studies presented—covering potential large pool fires from crude oil tanks, flash fires from asphalt tanks, overpressure and leaks from propane tanks, and overpressure and rupture of butane tanks—demonstrate the effectiveness of HAZOP in identifying process deviations, analyzing their causes and consequences, and recommending appropriate safeguards. The findings highlight the pivotal role of HAZOP in enhancing safety within tank farms and the broader Chemical Process Industry (CPI). This methodology is instrumental in preventing incidents and mitigating risks, thereby safeguarding people, businesses, and the environment. The proponents strongly advocate for the consistent application of HAZOP analyses as an essential practice for preventing LOPC scenarios and their potentially catastrophic consequences, whether as a proactive measure or in compliance with regulatory standards and requirements.

To ensure the effectiveness of HAZOP, it is crucial to enhance awareness of this methodology among industry professionals and stakeholders. By increasing understanding of HAZOP’s importance and benefits, broader adoption and more practical application in preventing LOPC scenarios can be achieved. Additionally, providing comprehensive training programs will equip personnel with the necessary skills to conduct HAZOP studies, focusing on understanding process deviations, analyzing their causes, and recommending adequate safeguards.

Organizations should also take the initiative to implement HAZOP studies as part of their internal safety management practices, even without regulatory mandates. A cost-benefit analysis often demonstrates that the long-term benefits of preventing incidents outweigh the costs of conducting HAZOP studies. Future research should explore the application of other PHA methodologies beyond HAZOP to gain a broader understanding of different approaches to risk assessment. Applying the HAZOP methodology to different processes or units within the Chemical Process Industry (CPI) would help determine its effectiveness in managing risks across various chemical processing environments, contributing to a more comprehensive approach to process safety management.

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