Issues of Concern in Evaluation, Estimation, and Analysis of Accidents and Catastrophes - Essay Example

ACCIDENTS AND CATASTROPHES Name: Institution: Course: Date: Accidents and Catastrophes Introduction There are a limited number of bulk petrol storage facilities in the United Kingdom that are important in playing a significant role as an energy source. The existence of these facilities has caused the UK to develop energy structures that is easily influenced by both the interaction and domestic energy situations. There is need for the continuous improvement of the safety measures, with a consideration to the designs and the general operation of the fuel storage systems. The report delivers on various issues of concern in evaluation, estimation and analysis of accidents and catastrophes. Determining the Probability Loss of Product Containment The probability of loss of the product containment can occur due to the long duration that is taken before the tanks are filled. The inclusive protection using the system using the high level switches, manual operation or the state detectors can be dormant for a long period and may fail to function or become faulty when there is need for them to perform the expected function. Those system malfunctions are the expected failure and danger to the product containment. Loss of product containment can also result from the automatic system failure to detect the overflow1. Considering the fact that there is manual operation of the bulk petrol storage facilities, it is important to determine the initiating event frequencies. The frequency of the manual operation by human can be based on two parameters, which include the task frequency per year and the human error probability (HEP) that can lead to the loss of product containment. The human error probability is assessed using an appropriate criterion that is selected from the table of generic task error probabilities. Suitable accounts and considerations are given to all the conditions that can have an impact to the operator and his or her ability to reliably and consistently perform the manual operation. The probability of human-initiated event, the frequency of the imitating the event can be calculated as follows. Event initiation frequency per year = task frequency per year X human error probability In this case, the human error probability is 10-6 and the task of refilling is carried out once a year with 50 fuel transfers into the tank. Therefore, Initiating event frequency = Task frequency (per year) X HEP = 50 X 0.00001 = 0.005 / year. According to the results, the initiation likelihood is considered as low, with the formula f < 10-4, /year. This is an indication that probability loss of product containment is very low and is not likely to occur within the expected lifetime of the plant operation. For example, three or more simultaneous automatic ultimate high-level device, valve and human failure is not likely to fail to perform the specific functions2. The automated high level device that is responsible for shutting down the valves during refill and the manual operation by the special operators are in accordance to the standard requirement and taking immediate action that ensures there is no loss of the product containment. The automated shutdown and manual operation ensures safety of an installation of the equipment’s, especially of the primary containment system. From the result obtained, it is quite clear that the BS EN 61511 standard requirements are followed. The stands requires that all the safety instrument systems (SIS) executing safety instrument function of SIL I and above, there should be a management system in place for the entire life cycle that ensure the management of all the appropriate measures. The realization of the likelihood of 0.005/year loss of product containment is contributed by the requirement in the management of SIS. One important requirement that go with the criterion on the protection of loss of product containment is the management of software’s and the configuration of the ultimate high-level device installed in the tanks. Additionally, the manual operation of the instruments follow the correct procedure and the evaluate the system performance on manual, validation and keeping of records3. Most importantly, the personnel’s in charge of the manual operation have a clear identification of the roles and responsibility while ensuring the probability of loss of product containment. According to the risk tolerance criteria, which is described as the limiting values for the likelihood of specified level of harm, the probability of loss of product containment is broadly acceptable having met the level of 1 x 10-6 per year. The Likelihood of the Incident Resulting In a Vapour Cloud Explosion and Fatality Petrol is one of the highly flammable liquids that require appropriate measures to be put in place while the liquid is on transport, storage or during offloading. Since the storage facilities are situated in clear areas of confinement, vapour cloud explosion (VCEs) can easily be ignores as one of the safety measures that need to be given keen consideration. While offloading, the spills or the overflow of the tanks could easily result to vapour cloud dispersion. Spillage of the petrol on the ground surface and off the storage tanks result in the creation of an expanding pool of liquid petrol together with the evaporation of the flammable vapours. the probability of the vapour exploding depends on the release rate and the spill property. Moreover, ambient conditions of the environment also contribute to the likelihood of the vapour explosion. The environmental factors that contribute to the likelihood of the explosion is mostly temperatures and wind4. Therefore, the modelling and the determination of the incidents that result into vapour cloud explosion and fatality caused by the flammable liquid petrol spills on the ground can be accomplished by utilizing a multipurpose consequence model. The flammable vapour cloud is intrinsically capable of getting ignited depending on the likelihood to explode with favourable conditions in place, hence causing a major fatality and accident to the environment. The immediate probable cause of the explosion could be accidental leaks especially if a valve is left open or the coupling is not done correctly, overfilling, failure of the bulk storage tank and flexible hose failure. From the table, it is stated that the probability if ignition is 0.1, which is then multiplied by the risk tolerance criteria of 10-6 so as to determine the likelihood of vapour cloud explosion in the next event. Immediate likelihood = probability if ignition x risk tolerance criteria = 0.1 x 10-6 =1 x 10-7 To determine the risk of fatality due to the probability of the vapour cloud explosion, the probability of ignition of fuel is provided as 0.1. Therefore; Risk of fatality due to fire = (probability of the mitigated event of vapour cloud explosion) x (probability of fatal injury in the event of an explosion) Risk of fatality due to explosion = (0.1x10-7) x (0.1) = 1x 10-8 Fault tree and conclusions Various guidelines are designed in the guidelines on the application of layer of protection analysis (LOPA) to the loss of product containment in the storage tanks. From the fault tree analysis shown above, the interaction of failures and other events likelihood are all presented. Comments on the Level of Risk against the Risk Tolerance Criteria The level of risk is defined as the probability or the likelihood of a potential hazard to cause injury to the operator, environmental hazard or damage of property. On the other hand, the risk tolerance criteria definition is based on human and environmental risks on the basis of the established industrial guidelines. The risk tolerance criteria of 10-6 is stated in the LOPA and it applies to all the environmental, Safety and financial risks that may occur as a result of the loss of product containment5. The description of the risk tolerance criteria in the petrol storage facility may be inappropriate due to the fact that environmental, safety and financial risks are supposed to be assessed separately with a consideration to the relevant criteria. According to the risk matrix for scenario based safety assessments, the risk tolerance criteria of 10-6/year are broadly acceptable. The fatality from the single scenario is much lesser compared to the tolerable category. From the calculations, a determination of the potential consequences as a result of product overflows causing the hazardous scenario is of low frequency per year.6 The valve misalignment contributes to the initiating event depending on the number of misalignment failures that have been recorded in the one-year period and consideration is given to the 50 fuel transfers that is done per year. The contributing factor to the reduced risk level is the regular maintenance of the facility and ensuring all the safety measures are followed when the storage tanks are operational. The conditional modifiers for the likelihood of ignition, personnel being in the affected are, and the probability of fatality are all calculated as a 0.1/ year. The statement in the LOPA presents a review ignition at various levels. In the case of the storage facility, the ignition is most likely to be caused by pressure imbalance and loss of product containment due to spillage. The value presenting the probability of ignition is generally acceptable and is based on the fact that vapour cloud that drifts under stable weather conditions is most likely to act as an ignition source. The probability of an operator being in the affected area is also given as 0.1. Though the figure may be an unjustifiable estimate, it is not clear on how large the affected area can be hence it is assumed that the area is minimal due to the available emergency response measures put in place. The area to be mostly affected is considered to be those that are close to the petrol storage tanks and not the entire site7. To summarise on the major comments on conditional modifiers, the estimated values provide are too low for a high-risk operation of the storage facilities. The assumptions for the values as generally made with consideration to the minimum level of the explosion area that can be affected. Weather is an important factor to be considered when making the estimations for the entire storage facility site. The protection layers considered in the data is manual fuel check, level gauge (PFT hardware), action of operator on sounding of alarm and operation of high level alarm and automatic shutdown. The first three protection layers are estimated at 0.1, with the operation of high level alarm, and automatic shutdown being estimated at 0.19. From the data, it is clear that manual operation is more efficient compared to the automatic operation systems. The preference for the automatic alarm response and shutdown is that the alarm level is based on float or the displacer tank level device. Therefore, there is a probability of generic failure of the device which pose a high level of hazard and loss of product containment due to the overflow of the product. The Role that Human Error in The Occurrence of a Major Incident Human error is basically involved in all the petroleum storage and refinery facilities. However, most of the reporting systems for the accidents are being designed based on theoretical framework of the human error. The role of human factor in occurrence of major incident in the industrial world is based on human factors that are influenced by the environment, job or organisation and at an individual level. According to the theoretical models of human error, there are three main frameworks involved. The first framework is on a traditional four stage model of processing information8. Secondly, a model of internal malfunction of the human that is stated by Rasmussen’s (1982) on skills, rules and knowledge model. Lastly, Reason (1990) proposal of unsafe acts model as a contributor to human error. The information processing model may not be specific to failure model, but it gives an explanation that most human errors are subjected to information processing theory. Therefore, the contribution of the error is through attention processes during operation a machine or plant. The error is stimulated by short-term sensory stores, pattern recognition, decision and response selection and finally the execution of the response. However, the attention processes is mostly influenced by the short-term and long-term memory that would result to the error while at work. The model of unsafe acts on other hand takes a different approach of human error that lead to failures or unsafe acts. Some of the human error can be behaviour based, either intentional or unintentional. For example, if the automatic shutdown fails to happen and the manual operator to fails to close the valve hence leading to loss of product containment. The error can be described as intentional. The error can be described as a mistake or a violation of responsibility at work. Considering the Hale and Glendon’s behaviour in the face of danger model, is a model based on scientific human error. The model explains human error based on human behaviour in entirety, with an explanation given on slips, accidents and errors. The face of danger model provides categories that human error as accident proneness. In this case, the role played by human error result from the environment, which are beyond the response capability of the human being. Moreover, the error can be as a result of human failure to cope with the demands due to personal characteristics. Secondly, engineering model as stated by Hale and Glendon result from the infrastructures and the failure of the inspected or to detect the risks and hazards before an accident9. Therefore, human play a role in escalating industrial accidents through the production of sophisticated, reliable engineering techniques used in the industries. The contribution can be caused by human reliability to adequately carry out a fault tree analysis as a logical exploration of engineering failure that can lead to an ultimate accident. Finally, the role of human error that can lead to the cause of an accident is further explained using interactive models that is based on the transfer of information. In case of a situation, the information presented may be incomplete or inaccurate. Measures to Increase the Level of Safety and Decrease the Level of Risk The barriers or measures to be introduced to increase the level of safety and decrease the risk level is by preparing various guidelines and regulations on emergency planning. As responsible personnel, it would be appropriate to work with various agencies that would be critical in designing emergency response and recovery plans and disaster management. The health and safety policy is the first document to be introduced at the workplace and must be followed by every individual. On the policy, Major Accident Prevention Policy (MAPP) should be designed to ensure important particulars that demonstrate that the operators have an established safety management system that account for the principles stated in the safety policy. The should be criterions to be followed in identifying foreseeable emergencies through a systematic analysis to ensure safety10. The emergency plan is to be subjected to continuous testing and review to respond to emerging emergencies and risk realised in the workstation and the entire site. It will also be important to train and engage the team in capacity building so that they are informed of the emergency response procedures and ways to identify risks and hazards are the workplaces. Finally, in an incident that risk is realised, the personnel who identifies that risk or the hazard should report to the relevant personnel that will engage in the management of the risk. Most importantly, all the staff should be well informed and ensure the use of safety equipment’s, wear reflective jackets and know the assembly points and location of the fire fighting equipment. Bibliography Bercha Engineering Limited. NGP TERMPOL Vapour Cloud Dispersion, Consequence, and Layer of protection analysis: Simplified process risk assessment Center for Chemical Process Safety (2001) ISBN 978 0 8169 0811 0 Chang JI and Cheng-Chung L ‘A study of storage tank incident’ Journal of loss prevention in the process industries (2006) 19 51-59 Model Code of Safe Practice Part 19: Fire precautions at petroleum refineries and bulk storage installations Energy Institute (2007) ISBN 978 0 85293 437 1 Tank inspection, repair, alteration, and reconstruction API STD 653 (Fourth edition) American Petroleum Institute (2009) Read More