Risk Analysis
Navigating Troubled Waters
Study seeks to mitigate transit vessel traffic mishaps in the treacherous Strait of Istanbul.
By Özgecan S. Ulusçu, Birnur Özba, Tayfur Altiok and Ihan Or
The Turkish Straits, which consist of the Strait of Istanbul and Çanakkale and the Sea of Marmara, have for centuries been one of the world's most strategic waterways since they constitute the Black Sea's sole maritime link to the Mediterranean and the open sea beyond. As such, the Straits are a vital passageway, not just for trade but for the projection of military and political power, while their extreme narrowness, winding contours and densely populated shores make navigation quite treacherous in these waterways.
The Strait of Istanbul is approximately 31 kilometers long, with an average width of 1.5 kilometers and a mere 660 meters at its narrowest point between Anadoluhisari and Rumelihisari [1]. It takes several sharp turns, forcing the ships to alter course at least 12 times, sometimes executing turns of up to 80 degrees. Navigation is particularly treacherous at the narrowest point, as the vessels approaching from opposite directions cannot see each other around the bends.
In addition to its winding contour, the unpredictable countervailing currents that may reach seven knots pose significant danger to vessels. Surface currents in the strait run from the Black Sea to the Sea of Marmara, while subsurface currents, 50 feet below the surface, run in the opposite direction. Within bays and near point bars, these opposing currents lead to turbulence. The unpredictable climate brings about further danger. During storms with strong southerly winds, the surface currents weaken or reverse in some places, making it even harder to navigate. Not surprisingly, all these elements can easily cause vessels transiting the strait to veer off course, run aground or collide.
The legal framework of vessel transit through the Strait of Istanbul is governed by the 1936 Montreux Convention [2]. When the Convention was put in place, less than 5,000 vessels passed through the strait annually, whereas today, changes in the shipping and navigational circumstances have led to a ten-fold increase in the maritime traffic through the strait.
Several reasons contributed to this immense increase. The Turkish Straits provide the only maritime link between the Black Sea riparian states and the Mediterranean, forcing these states to rely heavily on the Straits for foreign trade. The opening of the Main-Danube canal has linked the Rhine to the Danube, linking the North Sea and Black Sea. Traffic originating from the Volga-Baltic and Volga-Don waterways has also increased in the recent years.
Dangerous Cargo
Still, the most alarming increase in traffic is observed in the number of vessels carrying dangerous cargoes. The fall of the Soviet Union in 1991 has led to the emergence of newly independent energy-rich states along the Caspian Sea. Currently, a considerable percentage of the oil and gas from Azerbaijan, Turkmenistan and Kazakhstan reach the Western markets through the Turkish Straits. The maritime traffic will increase substantially since the production is expected to double by 2010. In addition, Russian oil companies are setting ever higher targets for production and export. Analysts predict that Russia could be pumping 10 million barrels of crude oil daily by the end of the decade, a significant portion of which is expected to pass through the Straits.
During the 1930s, when the Montreux Convention went into force, transport of hazardous materials posed little concern due to the infrequent passages and small vessel sizes. However, the increases in traffic and vessel sizes have raised the likelihood and the severity of accidents. The unusual characteristics of the Strait and its climate, coupled with the failure to request pilotage in this treacherous waterway, have led to more than 200 accidents in the past decade.
Major hazardous cargo accidents occurred since 1960 when the Greek-flagged M/T World Harmony collided with the Yugoslavian-flagged M/T Peter Zoranic, leading to the death of 20 crew members, severe oil pollution and fire that lasted several weeks, suspending the transit traffic. In 1979, Romanian-flagged Independenta and the Greek freighter M/V Evriyali collided at the southern entrance of the Strait. Forty-three crew members died, 64,000 tons of crude oil spilled into the sea and 30,000 tons burned into the atmosphere. In yet another catastrophe, the Greek Cypriot vessels M/T Nassia and M/V Shipbroker collided in the Strait. Twenty-nine officers and crewmen perished and 20,000 tons of crude oil burned for five days, suspending the traffic for a week. A potential disaster was averted only because the accident occurred just north of the city. In October 2002, Maltese-flagged M/V Gotia ran into the Emirgan pier in the Strait, spilling 18 tons of oil into the Strait. In February 2004, severe weather caused Cambodian-flagged M/V Hera to sink in the Black Sea, just a few miles off the northern entrance of the Strait. None of the 19 members of the crew survived [3].
In order to ensure the safety of navigation, life, property and to protect the environment, the Turkish government unilaterally adopted the 1994 Maritime Traffic Regulations for the Turkish Straits and Marmara Region. Four years later, the rules were revised and the 1998 Reviewed Regulations were adopted. These regulations include extensive provisions for facilitating safe navigation through the Straits in order to minimize the likelihood of accidents and pollution. The provisions aim to monitor the vessels with hazardous cargoes, regulate the patterns of vessel traffic by establishing new procedures for transit in the Straits, and attempt to account for dangerous meteorological and oceanographic conditions by restricting traffic under certain situations.
Even though the number of accidents decreased after the adoption of the regulations, the vulnerability of the Straits was evident once again in an incident in 1999. Voganeft-248, a Russian tanker, ran aground and broke apart at the Sea of Marmara entrance of the Strait. More than 1,500 tons of oil spilled into the sea, and clean-up efforts lasted several months [4].
The navigational hazards of the Strait of Istanbul are real and well known. Although strengthening transit restrictions and safety precautions have decreased the danger, accidents still happen. In 2005, almost 55,000 vessels passed through the Strait, an increase of 16 percent over the previous year. Inevitably, as the number of vessels transiting the Strait increases dramatically, so will the likelihood of accidents and environmental catastrophes, endangering the only city in the world that stands astride two continents, and its 12 million inhabitants. Therefore, determining accident risks and measures to mitigate these risks becomes of utmost importance.
The goal of the research described in this article is to analyze the risks involved in the transit vessel traffic in the Strait of Istanbul and provide suggestions to reduce safety risks. We have developed a detailed mathematical risk model to use in the risk mitigation process to improve safety in the Strait. In the first step of the risk analysis, the transit vessel traffic system in the Strait of Istanbul was thoroughly analyzed and a simulation model was developed to mimic maritime operations and surrounding environmental conditions as depicted in Figure 1.
Figure 1: A snapshot from the simulation model.
Risk analysis of the Strait was performed by incorporating a probabilistic accident risk model into the simulation model. Probabilistic arguments utilized historical accident data as well as subject-matter expert opinions. We have also performed a scenario analysis in order to study the behavior of accident risks and arrive at some critical policy suggestions.
Modeling Risk
As mentioned earlier, numerous incidents have resulting in an accident or a closure while a transit vessel navigates in the Strait of Istanbul. For example, there can be a mechanical failure in the vessel, or the captain or the pilot can make an error in the difficult geography of the Strait of Istanbul. These causal occurrences that may trigger an accident are referred to as instigators.
They include human error, rudder failure, propulsion failure, communication and/or navigation equipment failure and mechanical and/or electrical failure. Clearly, the occurrence of an instigator depends on the situation, which may be represented by a vector of situational attributes. Typical accidents that may occur in the Strait include collision, grounding, ramming, sinking and fire and/or explosion. Accidents may occur in chain in such a way that an accident may cause another one. First tier accident types include collision, grounding, ramming and fire and/or explosion, while the second tier accident types (that may occur following a first tier accident) include grounding, ramming, fire and/or explosion and sinking. Potential consequences of the first and second tier accidents include human casualty, property and/or infrastructure damage, environmental damage and loss of traffic effectiveness and throughput.
Defining situations is critical for risk analysis since they initiate instigators for accidents. Here we will introduce the concept of situational attributes to be able to define all the situations that may occur during a vessel transit. We divide the situational attributes into two groups: attributes influencing accident occurrence and attributes influencing consequences. The attributes influencing accident occurrence can be classified as vessel attributes and environmental attributes as given in Figure 2A and 2B. Similarly, attributes influencing consequences have two categories, vessel attributes and shore attributes, as listed in Figure 3.
Figure 2A: Situational attributes influencing accident occurrence.
Figure 2B: Situational attributes influencing the consequences.
Figure 3: Risk slices at the Strait of Istanbul.
Note that in order to quantify risks, we need to answer the following questions:
- How often do the critical situations occur?
- For a particular situation, how often do instigators occur?
- If an instigator occurs, how likely is an accident?
- If an accident occurs, what would the damage to human life, property, environment and infrastructure be?
In this study, risks are quantified based on historical data, expert judgment elicitation and a high-fidelity simulation model of the transit vessel traffic in the Strait of Istanbul. We have obtained a detailed vessel/traffic data from the Turkish Straits Vessel Traffic Services (VTS) and meteorological data from various resources. The simulation model mimics arrivals of five types of vessels — tanker, dangerous cargo carrier, LNG-LPG carrier, dry cargo carrier and passenger vessels — in various lengths and moves them according to traffic rules and regulations. The model also mimics the scheduling of vessel entrances, their pilotage and transit travel (with details such as speeds and overtaking) and their exit from the Strait along with all the relevant local traffic, weather and current conditions. The scheduling algorithm was developed through a close cooperation with the VTS to mimic their decisions on sequencing and scheduling vessel entrances in day times and night times, as well as the start time and length of the time-window regarding vessel traffic in either direction. The model was tested through a validation process and the results have been satisfactory.
In the model, the Strait of Istanbul is divided into 21 slices (each .92 miles long) for risk analysis purposes as depicted in Figure 3. The risk at a slice is calculated based on the snapshot of the traffic in that slice every time a vessel enters it.
In order to calculate risk, the product of two sets of factors associated with each transit is considered: 1. the probability of an accident, and 2. the potential consequences of this accident during that particular transit. Since two groups of accidents are considered — first- and second-tier accidents — slice risk can be calculated accordingly.
Pr (first-tier accident type) is obtained using conditional probabilities of all possible accidents given situations (e.g. visibility) and instigators (e.g. human error), conditional probabilities of instigators given situations and finally probabilities of situations.
Pr (second-tier accident type)is obtained using conditional probabilities of all possible second-tier accidents given first-tier accidents and probabilities of first-tier accident occurrences.
E [Consequence type/Accident type] is obtained using the consequence impact levels, conditional probabilities of all possible consequences given accidents and situations and finally probability of situation.
To be able to calculate risk, R, as shown in the equation, some of the accident probabilities (due to situations and instigators) and consequence probabilities (of accidents and situations) were obtained via elicitation of expert judgments. Other probabilities (e.g. instigator and second-tier accidents probabilities) were obtained from the historical data.
(click here to view a larger version in a separate window)
Experience has shown that maritime accidents can be quite different from one another in terms of factors causing them. As introduced earlier, various conditional probabilities of accidents were sought after in this study. Unfortunately, historical data were insufficient for a proper statistical analysis of these probabilities. Therefore, we have relied upon expert opinion in their estimation. Expert opinion on accident probabilities was obtained through an elicitation process using questionnaires focusing on pairwise, uni-dimensional (one at a time) comparisons of factor settings (while keeping the remaining factors at pre-determined fixed levels).
Accident consequences (in terms of low, medium or high effects on human life, traffic efficiency, property, infrastructure and environment) were also determined through a similar elicitation process. Furthermore, we have assumed that the quantitative values of impact levels (such as low, medium, high) of a consequence of an accident at a given slice are uniformly distributed within their associated scales. Their parameters are given in Table 1 for different levels of consequence impacts. These values do not represent the actual consequence of an accident in a specific unit (e.g. dollars or number of casualties). Instead, we utilize index values representing the experts' perception of a low, medium and high consequence. As a result, the calculated risk values are meaningful when compared to each other in a given context. Clearly, this may also be done in some common measure that may most likely be in monetary terms.
|
Finally, we have integrated these assessments into the simulation model such that the risks observed by each vessel at each slice were calculated considering all the natural and man-made conditions surrounding the slice (such as, vessel characteristics, pilot/tugboat deployment, proximity of other vessels, current and visibility conditions, location in the Strait etc.) as the vessels moved along the Strait.
Experimentation with the Model
We have incorporated the risk model described above into the simulation model developed to mimic the transit vessel traffic in the Strait of Istanbul. The risk profiles of the current operation in the Strait (the average and maximum risks) are shown in Figure 4A/B. The average risk profile exhibits a steady behavior from the north entrance all the way down to Bogazici Bridge where the local maritime traffic congestion starts in this highly populated area on the Strait. Interaction of the transit and local traffic patterns generates a tremendous spike in risk in Slice 19 (i.e. the area of the Strait between Besiktas-Uskudar-Salacak-Sirkeci districts of Istanbul, the main harbor region) and tapers off around the south entrance. The maximum risk profile also exhibits a similar behavior, yet with a more than 100-fold difference from the average to maximum observed risk at the spiked area. This has been a remarkable observation on how risky the transit vessel traffic is to city of Istanbul.
Figure 4A/B: Current risk profiles of the Strait of Istanbul.
We then performed a scenario analysis to evaluate the characteristics of accident risks in the Strait. This analysis has provided us with the ability to investigate how changes in various policies and practices impact the current risk profile of the Strait.
We have experimented with the model by changing vessel arrival rates and the scheduling practice to allow more or fewer number of vessels into the Strait, pilot availability and deployment level, overtaking conditions (i.e. relaxing or tightening the rules governing overtaking) and modifying local traffic density. Our investigations resulted in the following observations:
- The current vessel scheduling/sequencing procedure works remarkably well. Any change to allow more vessels into the Strait with the hope of reducing vessel waiting times will result in substantial increase in the safety risks. Similarly, any change to allow fewer numbers of vessels into the Strait with the hope of reducing risks will result in substantial increases in vessel waiting times at both entrances. These changes may need further investigation if the dangerous cargo traffic lessens significantly due to alternative routes or pipelines.
- Our investigation suggests that pilots are of utmost importance for safe passage, and lack of pilotage significantly increases the risks in the Strait. In the current practice, vessels greater than 250 meters in length are mandated to take a pilot, and it is voluntary for the rest. Thus, we recommend mandatory pilotage for vessels greater than 150 meters in length.
- Even though current regulations do not allow overtaking anywhere in the Strait, the risk model indicates that overtaking a vessel is less risky as opposed to forcing a following vessel to slow down behind a slow vessel. Therefore, in the areas where the width of the Strait tolerates it (except between Kanlica and Vaniköy), overtaking proves to be a safe practice as confirmed by the expert opinion.
- The most significant contributor to the risk appears to be the juxtaposition of the transit and local traffic. To reduce risks significantly, the scheduling procedure may be revised to encourage more of the dangerous cargo vessels to make nighttime transits. This requires further research on what kind of modifications can be done to the nighttime scheduling practice to control vessel delays at night.
Conclusion
The nature of the global economy dictates that the tanker traffic in the Strait of Istanbul cannot be eliminated. Nonetheless, the economic aspirations and environmental awareness need not to be mutually exclusive goals in the Strait. The risks involving the transit traffic can be mitigated by operational policies and restrictions that adequately regulate the transit vessel traffic while maintaining the freedom of passage. Until then, the environment, the priceless historical monuments and the health and safety of the city's residents will be at jeopardy.
In this study, we have carried out a comprehensive analysis of safety risks of the maritime traffic in the Strait of Istanbul. We have developed an understanding of the vessel transit operations in the Strait through a serious collaboration with the key parties such as Turkish Straits Vessel Traffic Services (VTS), among others. Consequently, we have developed a detailed hybrid mathematical/simulation model using data from a large number of sources. The model is a valid representation of the maritime traffic operations at the Strait of Istanbul and the results are highly accurate and realistic.
Our conclusions are in the direction of maintaining the current scheduling/sequencing procedures to let vessels enter the Strait, enforcing pilotage on an enlarged scale and moving the dangerous cargo vessels (which account for the largest chunks of risks) to night-time transit as much as possible, in order to reduce their interaction with the day-time local traffic.
Tayfur Altiok (altiok@rci.rutgers.edu) is the director of the Laboratory for Port Security and a professor in the I&SE department at Rutgers University, where Özgecan S. Ulusçu (ozgecanu@eden.rutgers.edu) recently earned her Ph.D. lhan Or (or@boun.edu.tr) is a professor in the Department of Industrial Engineering at Boaziçi University, Istanbul, Turkey, where Birnur Özba (birnur@ozbas.com.tr) is a Ph.D. student and research assistant.
|
References
- "Istanbul Eserleri, Rumelihisari," 2003, www.kentimistanbul.com, accessed July 10, 2008.
- "Convention Regarding the Regime of Straits," The American Journal of International Law, Vol. 31, No. 1, pp. 1-18.
- "Some of the major casualties in the Strait of Istanbul during the past years," 2005, Turkish Maritime Pilots' Association Web site (www.turkishpilots.org.tr), accessed July 8, 2008.
- Birpinar, M.E. and Talu, G.F. and Su, G. and Gulbey, M. and Istanbul, T., 2005, "The Effect of Dense Maritime Traffic On The Bosphorus Strait and Marmara Sea Pollution," available at http://balwois.mpl.ird.fr/balwois/administration/full_paper/ffp-746.pdf, accessed on July 8, 2008.
OR/MS Today copyright © 2008 by the Institute for Operations Research and the Management Sciences. All rights reserved.
Lionheart Publishing, Inc.
506 Roswell Rd., Suite 220, Marietta, GA 30060 USA
Phone: 770-431-0867 | Fax: 770-432-6969
E-mail: lpi@lionhrtpub.com
URL: http://www.lionhrtpub.com
Web Site © Copyright 2008 by Lionheart Publishing, Inc. All rights reserved.