© 2017 CEDCS Ltd

Risk Assessment

Another essential tool to help design a safe chemical plant

Risk Assessment is s simple process in principle. There’s a good basic guide published by the HSE (Note 1) for those who have no formal training but need to carry out simple risk assessments. In summary, the process is - 1. Look for the hazards - what can go wrong such that people, the environment or property could be harmed? 2. Consider who or what might be harmed, and how the harm comes about, and how much harm might be done. 3.  Consider the probability of this event occurring, as the risk equals the amount of harm multiplied by the probability of it happening. Then decide if the risk is acceptable. Nothing happens without some risk, but the aim of the Risk Assessment is to compare the estimated risk with what is considered acceptable, and then to reduce the risk (either the amount of harm likely to be done, or the probability of it occurring, or both). This process has to be repeated for all envisaged scenarios. Each scenario is assessed individually, but if many significant risks are identified, then the total risk to any risk group (persons, environment, and finance) should be evaluated to ensure that the total risk is acceptable, If in any case (either at individual risk or aggregated risk level) 4. Record your results for future records, 5. Review and revise your evaluation if anything changes. Technical Risk Assessments follow this principle the same as non-technical ones. In many cases, common sense or expert judgement is sufficient, but increasingly Risk Assessments have to use recognised principles and data to be considered acceptable, especially when significant risks (for example involving potential fatalities) are being considered. Experts in quantified risk assessment are needed, for example, when assessing serious risks on chemical plants. Such technical risk assessments are the foundation of designing formal safety systems, and when electronic or programmable safety systems (for example computer-based shutdown systems) are being designed, such systems have to comply to the standards that govern such systems (notes 2 and 3). A key input to such Risk Assessments is a Tolerability of Risk matrix. This is a formal framework for accepting various levels of risk if their probability is below certain maximum frequency criteria. A typical Tolerabilty of Risk matrix is shown below. Sometimes, formal procedures are used to identify the hazardous situations which are then risk assessed. Hazard Studies are examples of such procedures, and when a hazard is found in a Hazard Study, a risk assessment has to be carried out to decide if the risk is tolerable or requires effort to reduce it. Should the risk be Broadly Acceptable, the risk is usually accepted without further consideration (although it is always professionally mandatory to take measures to reduce even small risks where economically reasonable). If the risk is Unacceptable, then the situation cannot be accepted under any circumstances. When such a risk is discovered, actions must be placed to remedy the situation by resucing the severity of the hazard, reducing its probability of occurrence, or both, until the risk is reduced at worst to the “TIFALARP” region. If the risk is TIFALARP, then it is possible to accept the risk provided further risk reduction is not possible or is economically non-viable. However this is a situation where great care is required, as too many risks in the TIFALARP region is likely to aggregate to an overall unacceptable situation, and TIFALARP risks close to the intolerable region are much discouraged by the HSE. All risk assessment requires an experienced and skillful assessor if the results are to be credible. Technical risk assessment also required appropriate technical skills and experience.

CEDCS Ltd

Note 1 - HSE “Five steps to Risk Assessent”, , ISBN 0 7176 1565 0 Note 2 - BS EN 61508 “Functional Safety” Note 3 - BS EN 61511 “Functional Safety (process industry sector)”
GENERALISED TOR CHART 5 (serious) INTOLERABLE RISK CATEGORY TOLERABLE IF ALARP BROADLY ACCEPTABLE 1 (trivial) Very low FREQUENCY High Rare event Common event

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Risk Assessment

Another essential tool to help

design a safe chemical plant

Risk Assessment is s simple process in principle. There’s a good basic guide published by the HSE (Note 1) for those who have no formal training but need to carry out simple risk assessments. In summary, the process is - 1. Look for the hazards - what can go wrong such that people, the environment or property could be harmed? 2. Consider who or what might be harmed, and how the harm comes about, and how much harm might be done. 3.  Consider the probability of this event occurring, as the risk equals the amount of harm multiplied by the probability of it happening. Then decide if the risk is acceptable. Nothing happens without some risk, but the aim of the Risk Assessment is to compare the estimated risk with what is considered acceptable, and then to reduce the risk (either the amount of harm likely to be done, or the probability of it occurring, or both). This process has to be repeated for all envisaged scenarios. Each scenario is assessed individually, but if many significant risks are identified, then the total risk to any risk group (persons, environment, and finance) should be evaluated to ensure that the total risk is acceptable, If in any case (either at individual risk or aggregated risk level) 4. Record your results for future records, 5. Review and revise your evaluation if anything changes. Technical Risk Assessments follow this principle the same as non-technical ones. In many cases, common sense or expert judgement is sufficient, but increasingly Risk Assessments have to use recognised principles and data to be considered acceptable, especially when significant risks (for example involving potential fatalities) are being considered. Experts in quantified risk assessment are needed, for example, when assessing serious risks on chemical plants. Such technical risk assessments are the foundation of designing formal safety systems, and when electronic or programmable safety systems (for example computer-based shutdown systems) are being designed, such systems have to comply to the standards that govern such systems (notes 2 and 3). A key input to such Risk Assessments is a Tolerability of Risk matrix. This is a formal framework for accepting various levels of risk if their probability is below certain maximum frequency criteria. A typical Tolerabilty of Risk matrix is shown below. Sometimes, formal procedures are used to identify the hazardous situations which are then risk assessed. Hazard Studies are examples of such procedures, and when a hazard is found in a Hazard Study, a risk assessment has to be carried out to decide if the risk is tolerable or requires effort to reduce it. Should the risk be Broadly Acceptable, the risk is usually accepted without further consideration (although it is always professionally mandatory to take measures to reduce even small risks where economically reasonable). If the risk is Unacceptable, then the situation cannot be accepted under any circumstances. When such a risk is discovered, actions must be placed to remedy the situation by resucing the severity of the hazard, reducing its probability of occurrence, or both, until the risk is reduced at worst to the “TIFALARP” region. If the risk is TIFALARP, then it is possible to accept the risk provided further risk reduction is not possible or is economically non-viable. However this is a situation where great care is required, as too many risks in the TIFALARP region is likely to aggregate to an overall unacceptable situation, and TIFALARP risks close to the intolerable region are much discouraged by the HSE. All risk assessment requires an experienced and skillful assessor if the results are to be credible. Technical risk assessment also required appropriate technical skills and experience.

The Hazard Study process

The Hazard Study

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