HPCL CPM 3-PCP 5-Risk Anaylsis & Hazop Studies- PPT.pptx

The origins of the societal risk criteria in the uk

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The origins of the societal risk criteria in the UK can be traced back to the late 1970s, Ball & Floyd 1998. The Advisory Committee on Major Hazards suggested in 1976 that a serious accident in a particular plant was unlikely to occur more often than once in 10,000 years, which could be regarded on the border of acceptability, ACMH 1976. point N = 500 and F = 2 x 10-4 per year.
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Societal Risk and F-N Curves This has often been taken as an anchor point for the FN curve where the chance of an accident involving 10 or more fatalities should not exceed 1 in 10,000 per year. In the second Canvey report, HSE 1981, it was suggested that an event with 1,500 fatalities and the frequency of 2 x 10-4 per year (2 in 10,000) could be judged as intolerable.
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Societal Risk and F-N Curves The proposed slope of the FN curve was –1 (no risk aversion), based on historical record for the chemical industry. In the study, ACMH 1981, it was quoted as an upper maximum tolerable risk level a line of slope –1 through the
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Societal Risk and F-N Curves However, in HSE 2001, it is suggested that the risk of a single accident causing the death of 50 people or more with the frequency of 1 in 5,000 per annum can be considered as intolerable. The broadly acceptable level of risk is suggested as a line three decades lower than the upper tolerable line. This evolution of the upper tolerable level of risk over 20 years is presented in Figure 1, and clearly demonstrates the value of ALARP dynamics and the goal setting approach in reducing the upper level of tolerability of risk.
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Societal Risk and F-N Curves The quoted criteria are not systematically used in the UK, however HSE is using ARICOMAH risk integral, HSE 2003, for evaluation of societal risk. This approach is based on the accident with the highest number of fatalities Nmax and its frequency f(Nmax), which are used to evaluate an approximate level of the Potential Loss of Life (PLL) or the fatal accident rate, using the risk aversion exponent of 1.4 (slope of –1.4). The explanation for the choice of this exponent seems to be that it matches the historical data.
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Example – F-N Curves
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Acceptable & Tolerable Risks
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ALARP – LOW & HIGH LINE
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F-N Curve -
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Risk Contour
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Risk Transects
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Risk Transects
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Probability Of Ignition Size Of Cloud Probability Of Ignition Large vapour clouds 1 Smaller clouds of gases 0.1
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Hazop Study Steps Receipt in Storage Vessel Select A Vessel Explain general intention of the vessel and lines Select a line Explain the intention of the line Apply the first guide words Develop a meaningful deviation Examine possible causes Examine consequences Detect hazards Make suitable records Make for all possible deviations Repeat for all guide words
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Unit 10 Risk Reduction Measures Unit 10 Risk Reduction Measures
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Risk Reduction Measures
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Layers Of Protection
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Bow Tie
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What are barriers?
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  • Fall '19
  • Safety engineering, fault tree, Hazards

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