risk assesment
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Risk assesment Dr. I.M. Mishra Professor, Dept. of Chemical Engineering Dean, Saharanpur Campus Indian Institute of Technology, RoorkeeTRANSCRIPT
Dr. I.M. MishraProfessor, Dept. of Chemical Engineering
Dean, Saharanpur Campus
Indian Institute of Technology, Roorkee
Risk Assessment
By
Risk Assessment
Risk assessment is the qualitative and quantitative assessment of the hazards which could cause a high death toll.
A full assessment involves the estimation of the frequency and consequences of a range of hazards scenarios and the damages expected.
Damages include injury and loss of life, damage to the environment and equipment, loss of work, and finally also economic loss to the plant.
Typical Sequences of Events in a Risk assessment
A. Flammable ReleaseEmission-. vaporisation (if any) - air j entertainment-gas
dispersion ignition-flash fire or vapour cloud explosion.B. Toxic Release
Emission- vaporisation-air entrainment -gas dispersion.
Introduction
Risk Assessment of a Process Plant
Interaction Between Process Equipment/Instruments or Units
Series Systems
Parallel System
Availability and Unavailability
Probability of-Coincidence
Directing the analyst to ferret out failures deductively Pointing out the aspects of the system important in respect of the
failure of Interest Providing a graphical aid giving visibility to those in system
management who are removed from system design changes Providing options for qualitative on quantitative system reliability
analysis Allowing the analyst to concentrate on one particular system failure at
a time Providing the analyst with genuina insight into system behaviour.
Fussel (1976) notes that the fault tree analysis is of major value in
Risk Assessment Methods
Fault Tree Method
Basic Rules For Fault Tree Construction
Ground Rule 1 Write the statements that are entered in the event boxes as faults; state precisely what the fault is and when it occurs.
Ground rule 2 If the answer to the question, "Can this fault consist of a
component failure?" is "Yes, classify the event as a "stat-of-component fault". If the answer is "No”. Classify the event as a "state-of-system fault".
No Miracles RuleIf the normal functioning of a component propagates a fault sequence, then it is assumed that the component functions normally.Complete-the-Gate rule: All inputs to a particular gate should be completely defined before further 'analysis of anyone of them is undertaken.
No Gate-to-Gate RuleGate inputs should be properly defined fault events, and
gates should not be directly connected to other gates,
Event Tree Method
Typical steps in an event tree analysis
Identify an initiating event of interest. Identify the safety functions designed to deal with the
initiating event. Construct the event tree, and Describe the resulting accident event sequences.
Cause-Consequence Diagrams Hazards Estimation & Report Presentation
Forms of Presentation of Results of a Risk AssessmentA. Risk to workforce
Annual riskFatal Accident Rate (FAR)Osha incidence rate (IR)
B. Risk to PublicPhysical effects.
e.g. contours on the site mapIndividual Risk
e.g. contours on the site map, or annual risk at fixed location
Societal RiskFN TableFN curbeEquivalent annual fatalities
Acceptable Societal Risk
Fatality, Statistics for common industrial and non-industrial activities
General Risk Criteria Adopted