On 20 April 2010, several Transocean and BP executives arrived on the Deepwater Horizon oil rig, which had drilled a well in the Macondo field. Their agenda included discussing occupational health and safety with the workforce and to congratulate the crew for a 7-year record with no Lost Time Injuries (LTIs). As they spoke to the offshore team and observed them preparing to cap off the well before moving to a new drilling site, danger was building up deep below.
The Deepwater Horizon drilling rig was owned by Transocean, on hire to BP, in order to drill the Macondo field, estimated to contain over 50 million barrels of oil, two and a half miles below the seabed. The Deepwater Horizon was an ultra-deepwater, semi-submersible drilling rig. It had been under contract to BP in the Gulf of Mexico for approximately 9 years. Such a drilling rig was necessary at this location, as the water was almost 5,000 feet deep, creating enormous pressures at the well. To prevent the hydrocarbons (i.e., oil and gas) from rising upwards in the well to the surface, a heavy fluid (known as drilling ‘mud’) is injected into the shaft.
The role of the Deepwater Horizon was to drill into the reservoir, then seal the well – known as temporary abandonment – ready for a future production unit to recover the oil. Drilling rigs such as these are mobile, moving around the world for contracts with major oil companies such as BP. A production unit (which may be a floating facility or a semi-permanent unit fixed to the seabed) then connects to the well to recover the hydrocarbons, possibly staying on location for decades. Delays meant that the Deepwater Horizon was overdue to leave the Macondo well by six weeks. The Macondo well had proved to be challenging, earning it the nickname “the well from hell”.
At the time, Transocean was a major offshore drilling rig contractor with over a hundred of these drilling rigs under contract. The fees for such a rig (and the specialist crew) could be up to $1 million per day. This contractual relationship between Transocean and BP was to become a key issue in the legal proceedings that followed the incident.
Drilling the Macondo well was exploratory in nature, the objective was to collect data about the geology and quality of the oil and gas at its location. The crew of Deepwater Horizon were in the process of sealing the well (known as ‘capping it off’) before getting ready to move the drilling rig to a new location. As part of this process, the pressure balance in the well is tested to see whether pressure is increasing. This activity, planned in advance, was high-risk in terms of process safety (or ‘major hazard’ safety). However, the BP and Transocean executives were discussing occupational safety issues, such as working at height, hand-injury awareness and the hazards of dropped objects.
During their tours of the Deepwater Horizon, the executives could not fail to witness the ongoing discussions around how to perform the pressure tests and how to interpret the results. They expressed some concern, but were informed that all was going well. A blowout had occurred on another Transocean rig in the North Sea four months earlier, but the executives later testified that they were unaware of this or the internal advisory note produced.
During the afternoon, the process of replacing the heavy fluids in the well with seawater commenced. Unknown to the crew, oil was leaking into the well. As they removed the heavy ‘drilling mud’, they were unknowingly replacing it with a lesser volume of seawater due to the oil collecting at the bottom of the well. The imbalance of heavy drilling mud and lighter seawater occurred 43 minutes before the blowout. Due to several simultaneous operations (e.g., setting a cement cap on the well, easing tension on the drilling risers), and the drilling mud being transferred to an adjacent supply vessel, the crew were not closely monitoring the volumes of mud/seawater flowing in the well.
As the drilling mud was removed, the only physical barrier still in place was the BlowOut Preventer (BOP). This is a huge mechanical device that can close around the pipe, or as a last resort shear through and clamp the pipe, preventing hydrocarbons from reaching the rig. However, this barrier requires a timely response from a person on the rig.
Pressure continued to rise and that evening, methane gas expanded in the well, pushing the drilling mud up onto the rig. The high-pressure gas followed the mud onto the rig, where it found a source of ignition and exploded. The explosion and fires took the lives of eleven men, whose bodies were never recovered. The four executives and 111 workers were rescued, although there were many injuries.
The Deepwater Horizon rig burned for 36 hours and finally sank on 22 April 2010. Oil flowed from the Macondo well for 87 days. It is estimated that at least 4 million barrels of oil were spilled into the Gulf of Mexico before the well was controlled.
The Macondo well blowout is the worst offshore oil spill in history. Claims, settlements and clean-up costs have risen to more than $42 billion. Nearly 800km of coastline in Louisiana, Mississippi, Alabama and Florida was impacted.
There were many investigations into this disaster, including by the Chemical Safety and Hazard Investigation Board (CSB), National Commission, National Academy of Engineering, Department of Interior, Joint Investigation Team (US Coast Guard and Bureau of the Ocean Energy Management), Deepwater Horizon Study Group, BP and Transocean.
I can’t summarise all of the findings here – and I’m not going to outline all the technical details from the various reports. However, I provide some commentary below on the key human and organisational factors.
Investigations found that the disaster was preventable, and was caused by failures in risk management, technology, mechanical equipment, procedures, spill response planning and human factors.
There were failures in three categories of barriers:
- People (e.g., competency, leadership, culture)
- Plant (e.g., the hardware, control systems and the facility layout)
- Process (e.g., risk management systems).
History shows us that catastrophic events occur if there are failures in each of these three barriers. The investigations show that risks were taken with every barrier, partly on the assumption that other barriers would pick up any problems.
The loss of Deepwater Horizon was preventable. We can, with the benefit of hindsight, identify a series of mistakes that were made by the various organisations involved.
In order to prevent a blowout, there were several technical barriers in place and I have attempted to summarise hundreds of pages of analysis in a few paragraphs below:
- Cement job: The cement barrier did not isolate reservoir hydrocarbons. The quality of the cement slurry was not adequate.
- Cement evaluation: An independent evaluation of the cement job was neglected, on the assumption that the cement job had been a success.
- Well integrity test: BP and Transocean personnel determined that the well integrity test was successful, even though the results were not conclusive.
- Monitoring: The Macondo team did not properly monitor the well in the final hours leading up to the blowout (mainly because of the earlier declaration that both the cement job and the well integrity test had been successful).
- Blow-Out Preventer: the BOP failed on two accounts. The pipe rams failed to seal the well and the shear ram failed to shear the drill pipe. Given that the BOP was designed to operate most effectively if activated long before hydrocarbons flowed onto the rig, the monitoring failure above contributed to the failure of the BOP.
The incident response was certainly an unprecedented effort, with the clean-up involving 6500 vessels and approximately 47,000 people. The incident response was based around containment, dispersion and removal of oil. Initial plans were insufficient to seal the flowing well. Several containment measures were attempted but failed, and the well wasn’t sealed until 15 July 2010, almost three months after the blowout.
In his book Disastrous Decisions, Hopkins stated that the original spill response was “written to satisfy regulatory requirements rather than with any real concern about how effective it might be” (Hopkins, 2012).
The Swiss Cheese fallacy
The Swiss Cheese model (Reason, 1997) is a neat way of showing how several barriers must fail for an incident to occur. However, if some barriers are reliant on a previous barrier, then these barriers are not independent. Therefore, as in this case, the failure of one barrier (the inadequate cement job) led to the failure of other barriers. Although the Swiss Cheese model gives the impression that there are multiple layers of protection against an incident, this is not the case if the barriers are inter-related.
Cost versus safety?
A study of this incident provides an insight into the inevitable tension between operations and safety. Of the key decisions that were made prior to the blowout, almost all of these led to reduced cost and rig time – and the majority of them increased the risk.
The Macondo well was planned to cost BP around $96 million. But the well cost much more than BP anticipated, having to seek additional funds from project partners on several occasions. At the time of the blowout, BP had spent over $142 million on the well, which was more than 38 days behind schedule.
It is unclear to what extent these cost and time overruns impacted the decisions made or behaviours at head office, or on the rig itself, but we do know that it was a concern to at least some personnel on the rig.
Human and organisational factors
The various investigations into this disaster highlighted failures in technical decision making, failures of management, concerns with the regulatory framework for the offshore industry and numerous human factors.
Deepwater drilling requires significant technical and engineering challenges to be overcome; however, the industry, and this disaster, is largely about people.
Although actions by the offshore crew onboard the Deepwater Horizon directly contributed to the event, the crew had been set up to fail by much wider issues.
“The Macondo disaster was not, as some have suggested, the result of a coincidental alignment of disparate technical failures. While many technical failures contributed to the blowout, the Chief Counsel’s team traces each of them back to an overarching failure of management”National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, Chief Counsel’s Report, p.225
The well integrity test was a key barrier, but analysis of this shows that it was misinterpreted. The purpose of the well integrity test is to check that the cement seal was working prior to moving the rig away from the location. The crew knew from experience that it is very unlikely the well would fail the test and so the test was seen as a box-ticking exercise. The cement engineers declared the test a success, but they were looking for confirmation that the well was sealed, not investigating whether it was, or was not.
“Once the test had been declared a success, the driller and toolpusher appear to have put any concerns about the test behind them rather than increasing their vigilance” (National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, Chief Counsel’s Report, p.244).
There were some indications that the well had failed the integrity test: that oil and gas were passing the seal. However, these unexpected test results were explained away the with ‘bladder effect’. The team then applied another technique to find the confirmation that they were seeking, and once declared a success, the team moved on from any concerns about the test.
It appears that the team were looking for feedback that confirmed the view that they had already made about the integrity of the well. It didn’t help that there were simultaneous activities and other distractions.
I have defined Non-Technical Skills elsewhere on this website as “the cognitive, social and personal resource skills that complement technical skills and contribute to safe and efficient task performance” (International Association of Oil and Gas Producers, IOGP, 2014). In this incident, there were failures of several Non-Technical Skills, including inaccurate Situation Awareness and Decision-Making failures.
Situation Awareness can be defined as developing and maintaining a dynamic awareness of the situation and the risks present in order to think ahead about what may happen next.
Situation awareness: “Knowing what is going on, so you can figure out what to do next”.
Gaining good situation awareness in a team revolves around three key questions:
- What do they know that I need to know?
- What do I know that they need to know?
- What do none of us know that we need to know?
Inaccurate situational awareness often results in poor decision making and unnecessary risk taking. On a major hazard facility such as the Deepwater Horizon, these conditions increase the likelihood of an accident. From the investigations it is clear that the crew’s situation awareness (or lack of) played a pivotal role in the Macondo disaster.
- Crew members on the drill floor were not aware of dynamic and substantial changes in the status of the Macondo well.
- ‘Kicks’ from the well that signalled a blowout was imminent were not detected.
- Over a 45-min period, various data indicating an impending blowout were not acted upon (e.g., increases in drilling-pipe pressure, pressure differences between the drill pipe and kill line).
- The mudlogger was separate from the well operations crew and unaware of activities that impacted his understanding of the data he was meant to monitor.
There was an 80-minute period when the Toolpusher, Driller, Well Site Leader, and others discussed pressure discrepancies between the drill pipe and the kill line. This suggests that the crew recognised issues and had concerns. However, they did not appear to consider the possibility of well integrity loss.
Their incomplete understanding of the situation led the crew to falsely interpret the Negative Pressure Test (NPT) as successful. This misunderstanding influenced their subsequent decisions, which ultimately led to the blowout.
“systematic application of various Non-Technical Skills could have altered the interactions between rig personnel for the better”Chemical Safety and Hazard Investigation Board (CSB), Investigation Report, Volume 3, 2016, p.69
The crew appear to be confused, and were having difficulty interpreting the situation as it developed. They had concerns, but did not appear to understand the significance of the developing situation in the well. The crew’s mental models (“the picture that you have in your mind”) were not updated: and certainly, some of the crew would not have the experience to be able to form an accurate mental model. Therefore, the increasing pressure in the well was recognized as a concern, but was not interpreted as the well flowing.
In order to understand why the crew erroneously concluded that the well was stable, the investigation reports show that:
- The positive pressure test for the cement job of the casing conducted earlier in the shift (approximately 11am), had been deemed a success, thus providing a strong expectation that the forthcoming negative pressure test would also be successful.
- The 3pm pre-job safety meeting did not mention any contingency procedure should the test fail, thus priming the crew that the test would pass (i.e., setting an expectation).
- Information was not shared between the drill crew and the mud logger.
As late as 9.20pm, the senior Toolpusher was assured by the crew that “Everything was fine”. But 20 minutes later, drilling mud was flowing out of the well onto the Deepwater Horizon. At 9.49pm, high-pressure gas from the well reached the rig and ignited.
To summarise, the lack of situation awareness was a result of missing information, a failure to understand the significance of certain cues and a failure to revise mental models in the developing situation.
Social dynamics and group thinking
The majority of the crew members were tradesmen, without considerable experience in abstract engineering or physics concepts, making them more susceptible to accepting the Toolpusher’s interpretation of events (who explained the Macondo well issues as ‘the bladder effect’). The Toolpusher and Driller were both considered to be experienced, trusted and well respected. This may have validated the new information that they were telling the other drill crew members.
The investigations suggest that “group think” may have influenced the crew’s decision making. The crew were wanting to arrive at a consensus decision. There is considerable research to show that a feature of small groups is they seek a unanimous decision – everyone must agree. We also know that decisions made by groups are more likely to be risky than decisions taken by individuals (known as the “risky shift”).
As group consensus was that the Macondo well was safe, and therefore activities could continue, no individual was required to take responsibility for the decision to proceed.
Psychological safety includes a belief that the workplace is safe for speaking up with ideas, questions, concerns and even mistakes. It’s a sense of confidence that your voice is valued. However, a survey of Transocean crew working on the Deepwater Horizon rig a few weeks before the disaster highlighted that 46% of crew members surveyed felt that the workforce feared reprisals for reporting unsafe situations (National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, 2011, p.224).
Critical information was not communicated from one organisation to another (there were several contractors working on the Deepwater Horizon at any one time), or even within an organisation. For example, the offshore crew were not informed that the cement job might be more likely to fail at the Macondo well than elsewhere and to be extra vigilant. There are several cases of key decisions being made without complete information. The National Commission Report refers to these issues as “information compartmentalisation”.
During the unexpected results from well testing, the rig crew did not seek advice or support from experts onshore. The guidance as to when offshore personnel should consult the onshore team was not clear (and we know from other disasters that there may be a reluctance to seek help from remote engineering teams).
Four months prior to the Macondo blowout, a similar incident occurred on a Transocean drilling rig in the North Sea. Fortunately, although hydrocarbons flowed into the well, it was shut in before a blowout could occur. Transocean produced internal advisories about this event, but the lessons from this near miss do not appear to have been received by the Deepwater Horizon crew. An internal presentation included warnings such as “tested barriers can fail” and “risk perception of barrier failure was blinkered by the positive inflow test [negative pressure test]”. The National Commission Report states that “The relevant facts of the Macondo and North Sea incidents are the same”.
There was confusion amongst leadership as to who was accountable for key decisions.
At the beginning of April 2010, a major reorganization of BP’s exploration business unit (including the BP Macondo team) separated the engineering and operations into distinct Functions. Previously, the exploration business was organised by Project. The reorganisation created confusion during the Macondo project – there was a lack of clarity over authority, roles and responsibilities.
“Though it is understandable that no one would wish to take ownership of the well after the blowout, the Chief Counsel’s team found many instances in which nobody was taking ownership before the blowout”.National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, Chief Counsel’s Report, p.227
Besides the changes to reporting relationships, the reorganisation meant that many of the managers overseeing the Macondo project had only a few months of experience in their positions at the time of the disaster.
Procedures and competency
It is not possible to prescribe every detail of a drilling program in a written procedure, nor would it be practical for a crew to follow a written procedure step-by-step. The crew were to use their knowledge, experience and skills to undertake critical activities such as the Negative Pressure Test and Temporary Abandonment.
“the companies failed to provide the rig crew and well site leaders exercising that judgment with adequate training, information, procedures, and support to do their jobs effectively” (Chief Counsel’s Report, p.235).
However, procedures for such safety critical operations would outline agreed practices and provide guidance for potential events, such as a loss of well control. Procedures facilitate human performance by documenting the intended steps of a task.
Key rig procedures, such as the Temporary Abandonment plan were updated on several occasions during April 2010. The CSB investigation notes that this plan occurred without a formal process. The changes to this plan had the potential to negatively affect well control barriers, but the impact of those changes were not assessed.
“Changes to the well design and procedures made in the month prior to the blowout created risks that were not adequately addressed by the Macondo team” (Staff presentation to the National Commission, December, 2010).
In fact, it appears that the onshore team were struggling to keep up with operations on the Deepwater Horizon. Much-needed procedures were provided to the rig at the last minute. The crew had little time to digest these prior to undertaking the critical activities.
“Thus, at Macondo, the operator [BP] and drilling contractor [Transocean] each presumed the other was responsible for a proper negative test procedure. The crew was left to put together something to get the work done”Chemical Safety and Hazard Investigation Board (CSB), Investigation Report, Volume 3, 2016, p.101
The response to the well control event prior to the explosion suggests that the crew were insufficiently prepared to manage an escalating well control situation.
The Transocean crew of Deepwater Horizon worked offshore for 21 days at a time (a ‘hitch’, or ‘tour’), working 12-hour shifts. Although it’s not possible to make robust links between their working pattern and the incident, we do know that performance decreases as the periods of consecutive shift work increases. We also know that the ratio of fatalities and severe injuries to less severe injuries is markedly higher for hitches longer than 14 days.
At the time of the incident, the Driller and one Assistant Driller were on shift number 20 of 21; the second Assistant Driller was on shift 19 of 21; and the day shift Toolpusher was on day 20.
A safety culture survey conducted a few weeks before the incident contained comments from the crew that the 21-day pattern was causing fatigue. Comments from the crew included “On their last week, they seem like they are in another world” and “On the last week, you are so tired that you feel like a robot”.
The Mud-Gas Separator (MGS) is able to remove small amounts of gas from the drilling mud. This gas is then vented to atmosphere at a safe location. During the event, the rig crew diverted the high flow of hydrocarbons to the MGS, which overwhelmed the system.
The crew had the alternative option of diverting hydrocarbons overboard, which may have vented the majority of the gas safely. This diverter option may have given the crew more time to respond, reduced the likelihood of ignition, or may have reduced the consequences of the event. However, the design of the MGS allowed fluids from the riser to be diverted to the Mud-Gas Separator when the well was in a high flow condition (i.e. during a blowout).
Unfortunately, when the increasing flow of gas, oil, mud and water was diverted to the MGS, it vented hydrocarbons directly back onto the rig. Within minutes, large areas of the Deepwater Horizon were enveloped in a flammable mixture.
We must also consider the design of the well itself. For example, the office-based engineers who designed how the well would be plugged with cement made several decisions based on financial risks, without fully understanding the impact on safety. Decisions were made that increased the risk of cement failure. Chapter 4 of the Report to the President begins with a quote from a Macondo engineer’s email: “But, who cares, it’s done, end of story, [we] will probably be fine and we’ll get a good cement job.”
Operations related to the Macondo well required a heavy reliance on people: on human judgement in particular.
It would be wrong to focus on the actions and decisions of those people on the Deepwater Horizon drilling rig, or those staff onshore who were closely linked to the Macondo well. Hindsight is a powerful tool, and it’s easy to find fault, especially given the benefit of time and the huge resources applied to these detailed investigations.
But even so, the failures of the various organisations involved are not unique to those organisations. If you conclude that somehow these organisations are different to yourselves, then you will fail to learn the lessons. And there are many lessons here – not just for the oil and gas industry – but for all organisations.
The Report to the President concluded:
“The immediate causes of the Macondo well blowout can be traced to a series of identifiable mistakes made by BP, Halliburton, and Transocean that reveal such systematic failures in risk management that they place in doubt the safety culture of the entire industry” (National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, 2011, p.vii)
The Macondo disaster echoes those disasters that have gone before, across many industries. The recurring themes are missed warning signals, failure to share information and an inadequate appreciation for the risks involved. If, as the Columbia Accident Investigation Board concluded, “complex systems almost always fail in complex ways”, then where do we go from here?
When organisations operate at the very frontiers of technology, we can’t allow an understanding of the human factors involved to lag behind. Unfortunately, for all of those touched by this tragedy, in this case it did.
Terminology (who’s who)
Offshore Installation Manager (always abbreviated to OIM) is in charge of the drilling rig when it arrives at a location.
The Senior Toolpusher is the senior drilling operations supervisor, second only to the OIM in the chain of command.
Toolpushers are drilling managers who direct and supervise day-to-day drilling operations on a drilling rig.
Drillers and assistant drillers work in the drill shack and are responsible for operating drilling machinery and monitoring and controlling the well.
Floorhands and roustabouts provide the labour force for drilling operations.
This article is dedicated to the eleven men who lost their lives in the explosion and fires at the Macondo well on 20 April 2010:
Jason Anderson, Aaron Dale Burkeen, Donald Clark, Stephen Ray Curtis, Gordon Jones, Roy Wyatt Kemp, Karl Kleppinger, Jr., Keith Blair Manuel, Dewey A. Revette, Shane M. Roshto and Adam Weise.
CSB video: Deepwater Horizon Blowout Animation
This video, produced by the U.S. Chemical Safety and Hazard Investigation Board (CSB) in June 2014, provides a clear explanation of the drilling process and the role of the blowout preventer. The CSB is an independent, non-regulatory federal Agency charged with investigating serious chemical accidents. Its investigation of the Macondo incident was the largest investigation in its history, collecting almost one million documents.
Macondo Investigation Report, Volume 3, Report No. 2010-10-I-OS, U.S. Chemical Safety and Hazard Investigation Board (CSB), April 2016. The key issues in this report include human factors, organisational learning, safety performance indicators, risk management practices, corporate governance and safety culture. I have listed this volume 3 of the CSB investigation before the other volumes, because this part provides the most complete analysis of the human and organisational factors contributing to the incident. Although the industry is dependent upon human actions to maintain safe operations, the CSB investigation reveals a significant gap in the effective management of human factors in offshore operations. I was honoured to be asked by the CSB to review aspects of this volume prior to its publication.
Macondo Investigation Report, Executive Summary, Report No. 2010-10-I-OS, U.S. Chemical Safety and Hazard Investigation Board (CSB), April 2016. This is a 24-page summary of the investigation approach, the investigative challenges, key findings and conclusions, and a summary of recommendations. Previous investigation reports were limited by information available at the time, and this Executive Summary outlines several new insights and lessons previously unreported.
Macondo Investigation Report, Volume 1, Report No. 2010-10-I-OS, U.S. Chemical Safety and Hazard Investigation Board (CSB), June 2014. This volume provides a description of the Macondo incident, together with a description of deepwater drilling and temporary abandonment. It summarises information on the companies and entities involved in the drilling and temporary abandonment of the Macondo well, the well itself, the Deepwater Horizon rig, and the drilling crew aboard the rig on the day of the incident. It concludes with an incident description summary that identifies the failures in the hours leading up to the explosions and fires aboard the Deepwater Horizon. The summary of drilling and completion activities provides the foundation for the CSB’s technical, systemic, organisational, and regulatory analyses in subsequent report volumes.
Macondo Investigation Report, Volume 2, Report No. 2010-10-I-OS, U.S. Chemical Safety and Hazard Investigation Board (CSB), June 2014. This volume covers the technical failure analysis of the BOP (BlowOut Preventer), barrier management at Macondo and Safety Critical Elements. Ultimately, the blowout preventer was the only physical barrier that could have potentially contained well fluids, but only if the crew or emergency systems could have successfully engaged it. As the events of 20 April 2010 indicate, the BOP did not seal the well.
Macondo Investigation Report, Volume 4, Report No. 2010-10-I-OS, U.S. Chemical Safety and Hazard Investigation Board (CSB), April 2016. This volume addresses the US offshore safety regulation during and after Macondo, and attributes of an effective regulator and regulatory system. The CSB concludes that “Ultimately, the offshore regulatory changes made thus far do not sufficiently place the onus on industry to reduce risk or empower the regulator to ensure proactive and effective industry management and control of major hazards” (p.12).
Chief Counsel’s Report, National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, 2011. This document provides a number of technical, management and regulatory findings. Chapter 5 (“Overarching failures of management“) is particularly interesting from a human and organisational factors perspective. The introduction to this chapter states that “The failures at Macondo were not inevitable, and the Chief Counsel’s team sets them out here in the hope that they will not be repeated” (p.225).
Report to the President, National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling, 2011. This document is structured into three main parts: (1) The path to tragedy, (2) Explosion and aftermath, and (3) Lessons learned. It provides an excellent outline of the events leading up to the disaster and the events that followed. It is a thorough and very readable review – “Though it is tempting to single out one crucial misstep or point the finger at one bad actor as the cause of the Deepwater Horizon explosion, any such explanation provides a dangerously incomplete picture of what happened encouraging the very kind of complacency that led to the accident in the first place” (p.viii).
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