IE 419 Case Study 3: BP Oil Spill
George Monninger
James Mayeski
Siri Swayampu
Jassim Al Mulla
April 30, 2013
Executive Summary
On April 20, 2010, the disaster known as the BP oil spill occurred in the Gulf of
Mexico, which became the largest ocean oil spills in history. This accident is responsible
for catastrophic environmental contamination that still persists to this day and the
deaths of 126 crew members. Events such as these simply cannot continue to happen,
as the lives of employees and the environment are assets far too precious to lose.
Altogether, nine incidents were found to be responsible for the occurrence on the BP oil
drill rig. Using a variety of online resources and research and fault tree analysis, it was
possible to determine the events that caused the disaster and the relationships between
them. Using these relationships, a probability analysis was conducted to determine the
likelihood of such events occurring, dictating that there is a 0.94% chance of an
accident occurring on the BP oil drill rig.
Introduction
According to an article entitled “The eight failures that caused the Gulf oil spill”
from the website database www. newscientist. com3 , it is believed that eight different
events are responsible for the cause of the accident. These eight causes include poor
cement quality, a failure to notice the problem, a misinterpretation of the pressure test,
two valve failures, an overpowered separator, and no gas alarm or blow out preventer.
In addition to these eight causes of failure, an additional cause was discovered and
found to be the product of using sea water instead of standard drilling mud, which
causes additional stress on the seal of the well. A number of safety solutions are
available that can help prevent catastrophic accidents such as the BP oil spill. Through
the process of research and analysis, several approaches can be taken in order to
decrease the chance of an accident occurring in the future.
Objective
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Determine causes of the oil spill disaster.
Conduct a fault tree analysis depicting the accident.
Determine possible solutions to prevent such accidents.
Conduct a cost/benefit analysis to determine what safety precautions are
necessary at what cost.
Methods
Using a series of probabilistic models, it was possible to determine a number of
viable solutions to prevent a catastrophe such as the BP oil spill. Through the process
of research, it was possible to construct a fault tree diagram illustrating the root causes
of the accident. Probabilities were assigned to each of the nine root causes based on
likelihood of the event occurring. In reference to the fault tree diagram, it is more likely
that an event such as a valve failure occurs versus structural or concrete failure.
A series of probability relationships were then conducted based on the root
causes assigned to the fault tree. Probabilities were assigned to each of the nine events
according to the likelihood of an occurrence. According to chapter 8 of
Niebel’s Methods, Standards, and Work Design 2 , an “and” gate refers to the relationship
between probabilities in which all inputs must occur before an output event to
occur.With an “or” gate, any of the events related in the branch can occur, causing
output. Using these relationships, it was possible to calculate the total probability of an
accident occurring on the drill rig. The labels on the fault tree diagram indicate the
events on the probability calculations table.
Calculations of the total probability were performed in three separate steps. First,
the four lower combined probabilities of each “and” and “or” sequence were calculated.
Next, the two upper “or” probability relationships were calculated.
After the probability that the event was calculated, a cost-benefit analysis was
done. First, the cost of the accident was found. This cost was multiplied by the initial
probability to come up with the base criticality of the event.
Several remedies to the root causes were determined. Their probabilities were
found, and new values were calculated for the probability that the oil spill would happen.
Cost-benefit analyses were done for the recalculated probabilities as well. From this, a
Results
Reasonable probabilities were assigned to each of the root causes in order to
compute the probabilities of the systems of events occurring. The result of 0.94% is
considerably high based, especially when compared to the accident probabilities found
in various examples throughout the textbook, such as Example 8.6 on page 352. Figure
1 shows the fault-tree diagram, and Table 1 shows the assigned probabilities of each
event, as well as the probability that the oil spill could have happened. Table 2 shows
the base criticality of the oil spill, which was $396.2 million. Both the fault tree diagram
and the cost/benefit analysis can be seen in the appendix.
Several fixes to the root causes were identified. Table 3 shows the proposed
changes, the events that the changes affect, the new probabilities of the events, and the
new values of the probability that the oil spill could have happened. Table 4 shows the
cost-benefit analysis of the proposed fixes. According to the cost-benefit equation, the
best proposed solution is to inspect the cement. With this solution, the probability of the
oil spill drops to 0.16%, and the criticality drops to $67.5 million.
Discussion
The present case study uses concepts found in Chapter 82 of the text to evaluate
the BP oil spill that took place on 20th April 2010. Oil spills are considered some of the
most lethal accidents since their side-effects are often permanent and especially
harmful to the environment, mankind and animal life. Of all the oil related accidents till
date, BP oil spill stands out as the most prominent due to its severity of casualties. A
statement4 by the then CEO of BP, Tony Hayward, stressed that this accident was
caused by a series of faults rather than a single one. Taking in to account his statement,
a fault tree diagram was drawn in order to assess the causes of the spill in a deductive
manner.
Two main fault events were identified for the spill; namely, cement failure and
gas explosion. Each of these fault events were further studied to pinpoint the basic
events leading to the accident. The first fault event sealing failure had two basic events
like the usage of sea water instead of drilling mud and dodgy cement. According to a
report by the National Commission5, it is revealed that BP had been using seawater
instead of drilling mud to seal the borehole. The reason behind this practice had been to
cut costs. The term dodgy cement refers to the improper cement seal formulation
around the borehole.
The second fault event, explosion, had three sub events such as worker error,
system failure and safety failure. Worker error consisted of basic events like the crew
failing to identify the leak that occurred fifty minutes before the blast, misinterpreting a
pressure test and deciding to divert the blowout material on rig. Once the leak started
the crew onboard the rig had an option to divert the blowout material away from the rig
via pipelines. However, they decided to lead the blowout material on to the rig via a
separator instead. The separator is a device that is designed to separate gas trapped in
the mud. The use of separator to process large quantities of blowout material
overwhelmed it, causing flammable gas to surround the rig. The second sub event,
System failures, consisted of two basic events pertaining to the malfunction of
mechanical work pieces like failure of valve in the cement seal and valve in the blowout
preventer. The third and final fault event was safety failure. This was comprised of the
basic event relating to the crash in the rig’s gas alarm. The lack of battery power in the
gas alarm was the reason for malfunction. All of the above events were depicted in the
fault tree diagram, using a sequential order.
The next step was to identify the probability of each of these causes and possible
solutions to prevent these events from recurring. The issue of sealing failures was found
to occur with a probability of 0.16. This failure can be avoided by inspecting the cement
mixture beforehand to ensure acceptable adhesion properties. This inspection is
anticipated to cost BP $20,000 year. Also, the use of drilling mud for sealing should be
mandatory, irrespective of the costs. Saving $100,000 dollars by not using drilling mud
is not worth risking a possible catastrophic spill.
The worker or human errors such as failure to notice leak and misinterpretation
of pressure occur constitute a probability of 0.2. These can be prevented by subjecting
workers through a mandatory training workshop. This workshop will cost $10,000 and
will be teaching the crew a comprehensive checklist of tasks such as reading pressure
pumps, identifying flammable gas concentrations, and implementation of regulations
mandated by the Environmental Protection Agency (EPA) and Mineral Management
Service (MMS). Furthermore, an inspector with sufficient experience in the study of
petroleum and natural gas should be hired to oversee the leak operations and
supervision of crew. Without having an inspector onsite, the probability of accidents is
0.89.This additional safety measure would cost BP $100,000 a year.
To increase and ensure safety mechanisms onboard the rig, a complete revamp
of safety systems should be executed. This revamp will include multiple methane
detectors along the bore pipe along with duplicate valves installed on the cement
sealant and Blowout Preventer. This revamping cost a hefty price of a million dollars per
year. However, its execution will provide an extra layer of safety mechanisms to the rig,
while eliminating the 0.85 probability of a spill. Finally BP should invest in buying and
installing multiple gas alarms and Blowout preventers. This adjustment will cost $25,000
a year and has a 0.92 probability of preventing spills.
By taking in to account the individual probabilities of these basic events, the total
probability of accident was calculated. The base criticality was then determined by
multiplying the cost of the accident (42 Billion) and the accident probability (0.94). The
criticality and benefit values were then calculated for each individual prevention
measure, followed by the ratio of cost to benefit. The prevention measure with the least
value of cost to benefit ratio was chosen to be implemented. In this case, it turned out to
be cement inspection.
This result is justified, since carrying out this measure will stop the accident at the
neck. Proper inspection of cement sealant will also avert miniature leaks in the ocean
floor keeping the ecosystem and aquatic life safe. If there were no restriction on the
budget, then all of the above mentioned safety measure should be executed. Oil spills
leave a shadow of toxic and long lasting consequences in their wake. As fellow human
beings, the decision makers at BP should follow the utmost preventive measures in
order to preserve nature's delicate ecosystem. While not all accidents can be prevented,
certain steps should be taken to eliminate as much risk as possible.
Conclusion
Analyzing the events leading to the B.P. oil spill made it possible to develop a
system of probabilities and cost benefit analysis which can be used to decrease the
chances for events such as these to occur. Altogether, nine events were believed to be
the root cause of the accident, according to several internet sources. Because of these
root causes, there was a 0.94% chance that the oil spill could have occurred. The
criticality of the event was $396.2 million. By regularly inspecting the cement that made
up part of the oil rig, the probability of the accident could have been reduced to 0.16%.
Additionally, the critically would be reduced by $328.7 million to $67.5 million.
Appendix
Figure 1: Fault-Tree Diagram
Table 1: Initial Probability Calculation
Table 2: Initial Cost-Benefit Analysis
Table 3: Proposed Changes and Recalculated Probabilities
Table 4: Final Cost-Benefit Analysis
Works Cited
1. Durando, Jessica. "BP: 'Sequence of Failures' Caused Gulf Oil Spill." USA Today.
Gannett, 08 Sept.
2010. Web. 25 Apr. 2014.
2. Freivalds, Andris, and Benjamin W. Niebel. "8 Workplace and Systems Safety." Niebel's
Methods,
Standards, and Work Wesign. Boston: McGraw-Hill Higher Education, 2014. N. pag.
Print.
3. Mullins, Justin. "The Eight Failures That Caused the Gulf Oil Spill." New Scientist. N.p.,
08 Sept.
2010. Web. 24 Apr. 2014.
4. "BP Chief Tony Hayward's Statement in Full." Theguardian.com. Guardian News and
Media, 17 June 2010. Web. 30 Apr. 2014
5. "Macondo: The Gulf Oil Disaster, Chief Counsel's Report, 2011." Google Books.
National Commission on BP Deepwater Horizon Oil Spill and Off-Shore Drilling, Jan.
2011. Web. 30 Apr. 2014.