Per Hokstad | SINTEF - Academia.edu (original) (raw)

Papers by Per Hokstad

Research paper thumbnail of THE INTRODUCTION OF IEC 6151 1 IN NORWEGIAN OFFSHORE INDUSTR Y

This paper presents main results from a project that prepared a guideline for use of the standard... more This paper presents main results from a project that prepared a guideline for use of the standards IEC 61508 and IEC 61511 in the offshore industry of Norway. There is a focus on the determination of Safety Integrity Level (SIL) for main equipment. Also the paper will discuss the elements contributing to safety unavailability and the calculation of the Probability

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Research paper thumbnail of Failure modeling and maintenance optimization for a railway line

This paper presents a model for deterioration and repair of a railway line. The critical failure ... more This paper presents a model for deterioration and repair of a railway line. The critical failure is "broken line". Two main failure mechanisms are considered: either shock failure, i.e. an immediate critical failure (without "warning"), or the critical failure occurs as the result of a degradation process, i.e. a degraded failure (crack) occurs first. Various types of inspection and maintenance

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Research paper thumbnail of Generic Framework for Integrated Risk Management in Water Safety Plans

In the Guidelines for Drinking-water Quality, the World Health Organisation (WHO) concludes that ... more In the Guidelines for Drinking-water Quality, the World Health Organisation (WHO) concludes that end-product testing is not sufficient to guarantee safe drinking water to consumers. Such analyses are often completed after the water is consumed and they may not provide correct information regarding the health effects of the water. Instead, WHO recommends preparation of risk-based Water Safety Plans (WSP) from 'source to tap', which considers conditions in source waters, treatment systems and distribution networks. WSP is currently being implemented in several countries and is expected to become increasingly important for water management in both developed and developing countries. WSPs facilitate an increase in awareness and understanding of risk issues fundamental for providing safe drinking water. WHO provides general but not detailed information on risk assessment and risk management procedures in WSPs. The primary purpose of this paper is to describe a framework for a str...

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Research paper thumbnail of A method for risk modeling of interdependencies in critical infrastructures

Reliability Engineering & System Safety, 2011

ABSTRACT Failures in critical infrastructures may be hazardous to population, economy, and nation... more ABSTRACT Failures in critical infrastructures may be hazardous to population, economy, and national security. There can be strong interdependencies between various infrastructures, but these interdependencies are seldom accounted for in current risk and vulnerability analyses. To reduce probability and mitigate consequences of infrastructure failures, these interdependencies have to be assessed. The objective of this paper is to present a method for assessing interdependencies of critical infrastructures, as part of a cross-sector risk and vulnerability analysis. The method is based on a relatively simple approach applicable for practitioners, but may be extended for more detailed analyses by specialists. Examples from a case study with the Emergency Preparedness Group of the city of Oslo, Norway, are included.

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Research paper thumbnail of Reliability model for computerized safety systems

Proceedings., Annual Reliability and Maintainability Symposium, 1989

ABSTRACT A model for reliability prediction of computerized process shutdown systems is described... more ABSTRACT A model for reliability prediction of computerized process shutdown systems is described. Particular attention is given to the classification of component failures to ensure that all types of failures are included, and to the modeling of dependent (common-cause) failures. A dependent failure model called the multiple-error shock (MESH) model is introduced. The reliability calculation is illustrated for a subsystem, using 1-out-of-2 voting logic. Some remarks as to the overall degree of redundancy of a total system are given. The dependent-failure model itself should be applicable to quite general systems

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Research paper thumbnail of Operational safety analysis of FPSO - Shuttle Tanker collision risk reveals areas of improvement

Offshore Technology Conference, 2003

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Research paper thumbnail of RAMS Management of Railway Tracks

Handbook of Performability Engineering, 2008

... Department of Production and Quality Engineering The Norwegian University of Science and Tech... more ... Department of Production and Quality Engineering The Norwegian University of Science and Technology N ... 1, 2, 3, and 4 are identified, where the following maintenance situations apply: ... In order to optimize the maintenance effort, the maintenance point performance measures ...

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Research paper thumbnail of Ethical dilemmas in traffic safety work

Safety Science, 2008

ABSTRACT The paper presents some well-known ethical questions regarding priority setting of safet... more ABSTRACT The paper presents some well-known ethical questions regarding priority setting of safety work. Some traffic examples are applied to illustrate the dilemmas. Basic ethical principles are considered, i.e. approaches based on utility, fairness and discourse. We also discuss the various “dimensions” of utility and risk that could be taken into account. Ethical challenges related to the use of “willingness to pay” are also considered. A small-scale survey has been carried out regarding people’s priority setting of traffic safety measures. The main results of this survey are summarized to provide a background for a discussion of the ethical dilemmas.

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Research paper thumbnail of Loss of safety assessment and the IEC 61508 standard

Reliability Engineering & System Safety, 2004

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Research paper thumbnail of Overall strategy for risk evaluation and priority setting of risk regulations

Reliability Engineering & System Safety, 2006

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Research paper thumbnail of The analysis of failure data in the presence of critical and degraded failures

Reliability Engineering & System Safety, 1997

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Research paper thumbnail of Practical experience with a data collection project: the OREDA project

Reliability Engineering & System Safety, 1996

Experience data on the reliability of equipment has become vital to many types of engineering and... more Experience data on the reliability of equipment has become vital to many types of engineering and maintenance analyses. The consequences of incorrect design or poor maintenance may adversely affect: safety, the environment or cost in most categories of ...

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Research paper thumbnail of An overall model for maintenance optimization

Reliability Engineering & System Safety, 1996

... Abstract. This paper presents an approach for identifying the optimal maintenance schedule fo... more ... Abstract. This paper presents an approach for identifying the optimal maintenance schedule for the components of a production system ... Such a global approach to maintenance optimization requires expertise from various fields, eg, decision theory, risk analysis and reliability and ...

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Research paper thumbnail of Transparent reliability model for fault-tolerant safety systems

Reliability Engineering & System Safety, 1997

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Research paper thumbnail of A reliability model for optimization of test schemes for fire and gas detectors

Reliability Engineering & System Safety, 1995

ABSTRACT Safety system detectors must be tested periodically to check that they would respond to ... more ABSTRACT Safety system detectors must be tested periodically to check that they would respond to an actual demand. A detailed reliability quantification model is here given for fire and gas detectors. The main objective of the model is to provide a tool for a realistic quantification of the safety of a detector, using combinations of periodic tests (both manual and automatic). The model can be combined with a life cycle cost (LCC) model to identify a combination of detector design and test scheme for optimization of safety and acquisition/maintenance costs. The reliability modelling is based on a detailed failure classification and accounts for all types of safety-critical failures actually observed in operation. Thus, failures that are caused by design errors (and later triggered by specific inputs) are handled by the model. Also, failures introduced during the testing are modelled. The modelling includes an approach for assessing the total coverage of any combination of tests, utilizing expert judgements. A quantitative example comparing two different designs/test schemes is also presented.

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Research paper thumbnail of A risk influence model applied to North Sea helicopter transport

Reliability Engineering & System Safety, 2001

... Per Hokstad Corresponding Author Contact Information , E-mail The Corresponding Author , Erik... more ... Per Hokstad Corresponding Author Contact Information , E-mail The Corresponding Author , Erik Jersin E-mail The Corresponding Author and Terje Sten E-mail The Corresponding Author. ... By this the authors hope to promote the future use of this kind of risk models. ...

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Research paper thumbnail of A system approach to reliability and life-cycle cost of process safety-systems

IEEE Transactions on Reliability, 1995

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Research paper thumbnail of Estimation of Common Cause Factors From Systems With Different Numbers of Channels

IEEE Transactions on Reliability, 2006

The paper gives a resume of the Multiple Beta Factor Model, being a rather simple extension of th... more The paper gives a resume of the Multiple Beta Factor Model, being a rather simple extension of the beta factor model for common cause failures. In this new model, a number of beta factors are introduced, defined as the probability that one specific channel (element) has failed, given that j specific channels have failed. Here the system's constant hazard function due to common cause failures will be the product of the channels' hazard function, the beta factor, and finally a "configuration factor". The configuration factor is introduced to distinguish between the performances of various system configurations, and if data are not available some generic values could be used for these. The main topic of the present paper is the estimation of the parameters in this model. An overall estimator for the configuration factors is provided, using data from systems with different numbers of channels. This approach utilizes the so-called data mapping. The beta factor estimator of the new model is compared to the commonly used estimator in the beta factor model, and this standard estimator is found to be somewhat inconsistent. Some special cases of the new model are also considered.

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Research paper thumbnail of Failure Modeling and Maintenance Optimization

International Journal of Performability Engineering, Jul 1, 2005

Abstract: This paper presents a model for deterioration and repair of a railway line. The critica... more Abstract: This paper presents a model for deterioration and repair of a railway line. The critical failure is" broken rail". Two main failure mechanisms are considered: either shock failure, ie an immediate critical failure (without" warning"), or the critical failure occurs as the result of a degradation process, ie a degraded failure (crack) occurs first. Various types of inspection and maintenance are performed on the line. Inspection by Ultrasonic Inspection Cars (UIC) is carried out at regular intervals, and there is a probability q that the inspection ...

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Research paper thumbnail of Common Cause Failure Modeling: Status and Trends

This chapter presents a status of common cause failure (CCF) modeling. The well known betafactor ... more This chapter presents a status of common cause failure (CCF) modeling. The well known betafactor model is still the most commonly used CCF model. The strengths and limitations of this model are therefore outlined together with approaches to establish plant specific beta-factors. Several more advanced CCF models are also described with a special focus on the new multiple beta-factor model.

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Research paper thumbnail of THE INTRODUCTION OF IEC 6151 1 IN NORWEGIAN OFFSHORE INDUSTR Y

This paper presents main results from a project that prepared a guideline for use of the standard... more This paper presents main results from a project that prepared a guideline for use of the standards IEC 61508 and IEC 61511 in the offshore industry of Norway. There is a focus on the determination of Safety Integrity Level (SIL) for main equipment. Also the paper will discuss the elements contributing to safety unavailability and the calculation of the Probability

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Research paper thumbnail of Failure modeling and maintenance optimization for a railway line

This paper presents a model for deterioration and repair of a railway line. The critical failure ... more This paper presents a model for deterioration and repair of a railway line. The critical failure is "broken line". Two main failure mechanisms are considered: either shock failure, i.e. an immediate critical failure (without "warning"), or the critical failure occurs as the result of a degradation process, i.e. a degraded failure (crack) occurs first. Various types of inspection and maintenance

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Research paper thumbnail of Generic Framework for Integrated Risk Management in Water Safety Plans

In the Guidelines for Drinking-water Quality, the World Health Organisation (WHO) concludes that ... more In the Guidelines for Drinking-water Quality, the World Health Organisation (WHO) concludes that end-product testing is not sufficient to guarantee safe drinking water to consumers. Such analyses are often completed after the water is consumed and they may not provide correct information regarding the health effects of the water. Instead, WHO recommends preparation of risk-based Water Safety Plans (WSP) from 'source to tap', which considers conditions in source waters, treatment systems and distribution networks. WSP is currently being implemented in several countries and is expected to become increasingly important for water management in both developed and developing countries. WSPs facilitate an increase in awareness and understanding of risk issues fundamental for providing safe drinking water. WHO provides general but not detailed information on risk assessment and risk management procedures in WSPs. The primary purpose of this paper is to describe a framework for a str...

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Research paper thumbnail of A method for risk modeling of interdependencies in critical infrastructures

Reliability Engineering & System Safety, 2011

ABSTRACT Failures in critical infrastructures may be hazardous to population, economy, and nation... more ABSTRACT Failures in critical infrastructures may be hazardous to population, economy, and national security. There can be strong interdependencies between various infrastructures, but these interdependencies are seldom accounted for in current risk and vulnerability analyses. To reduce probability and mitigate consequences of infrastructure failures, these interdependencies have to be assessed. The objective of this paper is to present a method for assessing interdependencies of critical infrastructures, as part of a cross-sector risk and vulnerability analysis. The method is based on a relatively simple approach applicable for practitioners, but may be extended for more detailed analyses by specialists. Examples from a case study with the Emergency Preparedness Group of the city of Oslo, Norway, are included.

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Research paper thumbnail of Reliability model for computerized safety systems

Proceedings., Annual Reliability and Maintainability Symposium, 1989

ABSTRACT A model for reliability prediction of computerized process shutdown systems is described... more ABSTRACT A model for reliability prediction of computerized process shutdown systems is described. Particular attention is given to the classification of component failures to ensure that all types of failures are included, and to the modeling of dependent (common-cause) failures. A dependent failure model called the multiple-error shock (MESH) model is introduced. The reliability calculation is illustrated for a subsystem, using 1-out-of-2 voting logic. Some remarks as to the overall degree of redundancy of a total system are given. The dependent-failure model itself should be applicable to quite general systems

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Research paper thumbnail of Operational safety analysis of FPSO - Shuttle Tanker collision risk reveals areas of improvement

Offshore Technology Conference, 2003

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Research paper thumbnail of RAMS Management of Railway Tracks

Handbook of Performability Engineering, 2008

... Department of Production and Quality Engineering The Norwegian University of Science and Tech... more ... Department of Production and Quality Engineering The Norwegian University of Science and Technology N ... 1, 2, 3, and 4 are identified, where the following maintenance situations apply: ... In order to optimize the maintenance effort, the maintenance point performance measures ...

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Research paper thumbnail of Ethical dilemmas in traffic safety work

Safety Science, 2008

ABSTRACT The paper presents some well-known ethical questions regarding priority setting of safet... more ABSTRACT The paper presents some well-known ethical questions regarding priority setting of safety work. Some traffic examples are applied to illustrate the dilemmas. Basic ethical principles are considered, i.e. approaches based on utility, fairness and discourse. We also discuss the various “dimensions” of utility and risk that could be taken into account. Ethical challenges related to the use of “willingness to pay” are also considered. A small-scale survey has been carried out regarding people’s priority setting of traffic safety measures. The main results of this survey are summarized to provide a background for a discussion of the ethical dilemmas.

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Research paper thumbnail of Loss of safety assessment and the IEC 61508 standard

Reliability Engineering & System Safety, 2004

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Overall strategy for risk evaluation and priority setting of risk regulations

Reliability Engineering & System Safety, 2006

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The analysis of failure data in the presence of critical and degraded failures

Reliability Engineering & System Safety, 1997

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Practical experience with a data collection project: the OREDA project

Reliability Engineering & System Safety, 1996

Experience data on the reliability of equipment has become vital to many types of engineering and... more Experience data on the reliability of equipment has become vital to many types of engineering and maintenance analyses. The consequences of incorrect design or poor maintenance may adversely affect: safety, the environment or cost in most categories of ...

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Research paper thumbnail of An overall model for maintenance optimization

Reliability Engineering & System Safety, 1996

... Abstract. This paper presents an approach for identifying the optimal maintenance schedule fo... more ... Abstract. This paper presents an approach for identifying the optimal maintenance schedule for the components of a production system ... Such a global approach to maintenance optimization requires expertise from various fields, eg, decision theory, risk analysis and reliability and ...

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Research paper thumbnail of Transparent reliability model for fault-tolerant safety systems

Reliability Engineering & System Safety, 1997

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A reliability model for optimization of test schemes for fire and gas detectors

Reliability Engineering & System Safety, 1995

ABSTRACT Safety system detectors must be tested periodically to check that they would respond to ... more ABSTRACT Safety system detectors must be tested periodically to check that they would respond to an actual demand. A detailed reliability quantification model is here given for fire and gas detectors. The main objective of the model is to provide a tool for a realistic quantification of the safety of a detector, using combinations of periodic tests (both manual and automatic). The model can be combined with a life cycle cost (LCC) model to identify a combination of detector design and test scheme for optimization of safety and acquisition/maintenance costs. The reliability modelling is based on a detailed failure classification and accounts for all types of safety-critical failures actually observed in operation. Thus, failures that are caused by design errors (and later triggered by specific inputs) are handled by the model. Also, failures introduced during the testing are modelled. The modelling includes an approach for assessing the total coverage of any combination of tests, utilizing expert judgements. A quantitative example comparing two different designs/test schemes is also presented.

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Research paper thumbnail of A risk influence model applied to North Sea helicopter transport

Reliability Engineering & System Safety, 2001

... Per Hokstad Corresponding Author Contact Information , E-mail The Corresponding Author , Erik... more ... Per Hokstad Corresponding Author Contact Information , E-mail The Corresponding Author , Erik Jersin E-mail The Corresponding Author and Terje Sten E-mail The Corresponding Author. ... By this the authors hope to promote the future use of this kind of risk models. ...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A system approach to reliability and life-cycle cost of process safety-systems

IEEE Transactions on Reliability, 1995

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Estimation of Common Cause Factors From Systems With Different Numbers of Channels

IEEE Transactions on Reliability, 2006

The paper gives a resume of the Multiple Beta Factor Model, being a rather simple extension of th... more The paper gives a resume of the Multiple Beta Factor Model, being a rather simple extension of the beta factor model for common cause failures. In this new model, a number of beta factors are introduced, defined as the probability that one specific channel (element) has failed, given that j specific channels have failed. Here the system's constant hazard function due to common cause failures will be the product of the channels' hazard function, the beta factor, and finally a "configuration factor". The configuration factor is introduced to distinguish between the performances of various system configurations, and if data are not available some generic values could be used for these. The main topic of the present paper is the estimation of the parameters in this model. An overall estimator for the configuration factors is provided, using data from systems with different numbers of channels. This approach utilizes the so-called data mapping. The beta factor estimator of the new model is compared to the commonly used estimator in the beta factor model, and this standard estimator is found to be somewhat inconsistent. Some special cases of the new model are also considered.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Failure Modeling and Maintenance Optimization

International Journal of Performability Engineering, Jul 1, 2005

Abstract: This paper presents a model for deterioration and repair of a railway line. The critica... more Abstract: This paper presents a model for deterioration and repair of a railway line. The critical failure is" broken rail". Two main failure mechanisms are considered: either shock failure, ie an immediate critical failure (without" warning"), or the critical failure occurs as the result of a degradation process, ie a degraded failure (crack) occurs first. Various types of inspection and maintenance are performed on the line. Inspection by Ultrasonic Inspection Cars (UIC) is carried out at regular intervals, and there is a probability q that the inspection ...

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Research paper thumbnail of Common Cause Failure Modeling: Status and Trends

This chapter presents a status of common cause failure (CCF) modeling. The well known betafactor ... more This chapter presents a status of common cause failure (CCF) modeling. The well known betafactor model is still the most commonly used CCF model. The strengths and limitations of this model are therefore outlined together with approaches to establish plant specific beta-factors. Several more advanced CCF models are also described with a special focus on the new multiple beta-factor model.

Bookmarks Related papers MentionsView impact