The Institution of Fire Engineers Hong Kong Branch. Professional Lecture Series on Fire Risk Assessment

Transcription

1 The Institution of Fire Engineers Hong Kong Branch Professional Lecture Series on Fire Risk Assessment Lecture 2 Qualitative Fire Risk Assessment Ir. M.C. Hui BSc(Eng) Hons, MEng (Building Fire Safety and Risk Engineering) CEng, CPEng, PE, MIFE, MSFPE, MCIBSE, MIAFSS, MHKIE, MIEAust Associate Director, Arup Fire Ove Arup & Partners Hong Kong Limited 1of 63 Contents of this Lecture Series Lecture 1: The Many Facets of Risk ( ) Lecture 2: Introduction to Qualitative Fire Risk Assessment ( ) Lecture 3: Introduction to Quantitative Fire Risk Assessment ( ) 2of 63

2 What is fire risk? Fire risk is a summary measure derived from a fire risk function, e.g. risk = f (probability, consequence of a given scenario), for all scenarios. In more layman terms, fire risk is the combination of fire scenarios, probability of occurrence of these scenarios, and the consequence of these scenarios when they occur. 3of 63 Risk Assessment is only part of the Big Picture Risk Management Process Overview (adopted from AS/NZS 4360:2004) 4of 63

3 The risk management process in details (adopted from AS/NZS 4360:2004) 5of 63 Main elements of the risk management process 1. Communicate and consult Communicate and consult with internal and external stakeholders as appropriate at each stage of the risk management process and concerning the process as a whole. 2. Establish the context Establish the external, internal and risk management context in which the rest of the process will take place. Criteria against which risk will be evaluated should be established and the structure of the analysis defined. 6of 63

4 Main elements of the risk management process 3. Identify risks Identify where, when, why and how events could prevent, degrade, delay or enhance the achievement of the objectives. 4. Analyse risks Identify and evaluate existing controls. Determine consequences and likelihood and hence the level of risk. This analysis should consider the range of potential consequences and how these could occur. 7of 63 Main elements of the risk management process 5. Evaluate risks Compare estimated levels of risk against the preestablished criteria and consider the balance between potential benefits and adverse outcomes. This enables decisions to be made about the extent and nature of treatments required and about priorities. 6. Treat risks Develop and implement specific cost-effective strategies and action plans for increasing potential benefits and reducing potential costs. 8of 63

5 Main elements of the risk management process 7. Monitor and review It is necessary to monitor the effectiveness of all steps of the risk management process. This is important for continuous improvement. Risks and the effectiveness of treatment measures need to be monitored to ensure changing circumstances do not alter priorities. 9of 63 Risk assessment Identify risk Analyse risk Evaluate risk 10 of 63

6 Identify risk Recognizing that a hazard exists and trying to define its characteristics is called risk identification. Comprehensive Identification using a wellstructured systematic process is critical (risk not identified may be excluded from further analysis). What can happen, where and when comprehensive list of sources of risks and events that might have an impact on the achievement of each objective identified in the context. Why and how it can happen possible causes and scenarios; important that no significant causes are omitted. 11 of 63 Tools for qualitative fire risk analysis Checklist A listing of hazards and recommended practices. Practical tool to support analysis of a building relative to a code or standard that forms the basis for the checklist. Helps the fire safety engineer to focus on requirements that are applicable to a specific project. Long list of readily visible / measurable fire safety factors or short list conceptual feature requiring interpretation. Checklists do not and cannot distinguish the relative importance of fire risk factors. 12 of 63

7 Tools for risk identification Narratives A series of recommendations things to do and not to do related to fire risk and safety. Descriptions of various hazardous conditions and ways to reduce or eliminate them, based on past observations of fires and their consequences. Earliest approach led to advice from parent to child on avoidance of fire dangers. Piecemeal parent s advice format evolved over time and developed into the present set of the NFPA Fire Codes (similarly into prescriptive building regulations and codes in other countries). 13 of 63 Tools for risk identification Narratives No attempt to quantitatively evaluate the fire risk, instead, compliance with published recommendations = acceptable. Rigid: Design either passes or fails, with no capability to cover for various conditions of human activities and different fire hazard conditions. The residual risk remaining if the design passes is never quantified or evaluated. 14 of 63

8 Tools for risk analysis In the chemical process industry, qualitative methods are used to identify the most hazardous events. What-if Identify hazards, hazardous situations, or specific accident events that could result in undesirable consequences. Hazard and Operability Study (HAZOP) Identify system deviations & their causes that can lead to undesirable consequences. Determine recommended actions to reduce the frequency and/or consequences of the deviations. 15 of 63 Hazard ID System/Location Mode Hazard Cause Consequence Smoke 1 Smoke Control Maintenance Worker accident when cleaning smoke vents at roof. Worker injured Injury Smoke 2 Smoke Control Maintenance Worker accident when maintaining smoke beam detectors, pneumatic pipework or inside Worker trapped or falling face of smoke vents Injury, fatality due to fall Smoke 3 Smoke Control Power Failure Smoke vents failing to open power failure smoke trapped in building Mitigation A mobile scaffold platform is designed to allow access to all exhaust louvres at the roof. Refer to High Level Access - Recommendations Report. Frequen Severity Risk Remarks/Update/Action cy No further action required Assessment Engineers' Assessment Follow-up Action Closed Access to inside face of smoke vents, pneumatic pipework and inside face of smoke vents at high level is provided by catwalks - refer to High Level Access - Recommendations Paper. Scaffold systems shall be used where necessary to gain access to high levels where the catwalk cannot reach. Procedural issue Procedures to be put in place for accessing all areas of the building Engineers' for maintaining smoke beam Assessment detectors, pneumatic pipework and inside face of smoke vents. Bldg operator to implement procedures for safe operation Smoke vents are activated by pneumatic lines. The vents are grouped into 15 smoke zones and planned in groups of eight. The system is designed 1 such that smoke vents open independently. The 3 3 No further action required smoke vents are held closed by air pressure - should the system fail, the vents open. Engineers' Assessment Closed 16 of 63

9 Tools for risk analysis (cont.) Preliminary Hazard Analysis (PrHA) A broad, initial study used in the early stages of system design. Identify apparent hazards. Assess the severity of potential accidents that could occur involving the hazards, and Identify safeguards for reducing the risks associated with the hazards. Focuses on identifying weaknesses early in the life of a system, hence saving time and money that might be required for major redesign if the hazards were discovered at a later date. 17 of 63 Tools for risk analysis (cont.) PrHA characteristics Relies on brainstorming and expert judgment. Typically performed by one or two people who are knowledgeable about the type of activity in question. They participate in review meetings of documentation and field inspections, if applicable. Applicable to any activity or system. Used as a high-level analysis early in the life of a process. Generates qualitative descriptions of the hazards related to a process, and provides a qualitative ranking of the hazardous situations that can be used to prioritise recommendations for reducing or eliminating hazards in subsequent phases of the life cycle. 18 of 63

10 Tools for risk analysis (cont.) PrHA characteristics Quality of evaluation depends on quality and availability of documentation, training of the review team leader, and experience of the review teams. Generally applicable for almost any type of risk assessment application, but focuses predominantly on identifying and classifying hazards rather than evaluating them in detail. Most often conducted early in the development of an activity or system, when there is little detailed information or there are few operating procedures. Often a precursor to further risk assessment. 19 of 63 Tools for risk analysis (cont.) 20 of 63

11 Tools for risk analysis (cont.) Risk Assessment Matrix Tables Frequency and consequences qualitatively described, yet risk is described quantitatively. 21 of 63 Tools for risk analysis (cont.) Risk Assessment Matrix Tables A list can be developed that prioritises and categorizes risk. From this list, attention can be focused on the appropriate areas and system changes, or suggestions are developed. 22 of 63

12 Tools for risk analysis (cont.) Risk Assessment Matrix Tables Return Period Consequence Frequency Negligible Marginal Critical Catastrophic 1 month Frequent B A A A 1 year Probable C B A A 10 years Occasional C B B A 100 years Remote D C B B 1,000 years Improbable D D C C 10,000 years Incredible D D D D Class A Class B Class C Class D Intolerable, shall be eliminated Undesirable, and shall only be accepted when risk reduction is impracticable Tolerable, with the endorsement of the project safety review Tolerable with the endorsement of normal reviews 23 of 63 Tools for risk analysis (cont.) Consequence Assessment and Cause Consequence Diagrams Developed for the purpose of assessing and propagating the conditional effects of a failure using a tree representation. Analysis starts with selecting a critical event. The logic works both backward (similar to fault trees) and forward (similar to event trees). 24 of 63

13 Tools for risk analysis (cont.) Fault trees Fault tree analysis can be used to qualitatively or quantitatively analyse fire risk or safety of the whole fire protection system or a component. A "fault" tree is effectively a statement of what events have to occur together to bring about an undesired outcome. Traditionally these have been drawn top-down and therefore the undesired event known as the "top event". 25 of 63 Tools for risk analysis (cont.) Success trees In a success tree, the "top event" is defined in terms of what makes the system operate to its specification. Reliability engineers conceptually prefer "success" tree analysis to "fault" tree analysis. The concept is similar but the Boolean mathematics in the construction of the tree is reversed ('or' gates become 'and' gates) because of this focus on availability (the desired outcome) rather than the fault (the undesired outcome). 26 of 63

14 Tools for risk analysis (cont.) Event trees An event tree is a visual representation of all the events that can occur in a system. It can be used to analyse systems in which components involve sequential operations or transitions. All the events stem from the initiating event, which starts the sequence of events. In fire safety, event tree analysis is one way to build up a reasonable picture of the likelihood of fire scenarios using our understanding of mechanisms by which fire occurs, spreads, and is controlled. Event trees are traditionally drawn top-down but trees drawn sideways are also common. 27 of 63 Tools for risk analysis (cont.) Event trees 28 of 63

15 Evaluate risk The purpose of risk evaluation is to make decisions, based on the outcomes of risk analysis, about which risks need treatment and treatment priorities. 29 of 63 Evaluate risk Risk evaluation involves comparing the level of risk found during the analysis process with risk criteria established when the context was considered. Basically it is a component of risk assessment in which judgments are made about the significance and acceptability of risk. In some circumstances, the risk evaluation may lead to a decision to undertake further analysis. 30 of 63

16 Evaluate risk (The ALARP Principle) Unacceptable region Risk cannot be justified save in extraordinary circumstances Tolerable only if risk reduction is impracticable or if its cost is greatly disproportionate to the improvement gained The ALARP or Tolerability region (Risk is undertaken only if a benefit is desired) Tolerable if cost of reduction would exceed the improvement gained Broadly acceptable region (No need for detailed working to demonstrate ALARP) Necessary to maintain assurance that risk remains at this level Negligible risk 31 of 63 Evaluate risk (The ALARP Principle) What is meant by reasonably practicable? You may come across it as SFAIRP ( so far as is reasonably practicable ) or ALARP ( as low as reasonably practicable ). The two terms are interchangeable except if you are drafting formal legal documents you must use the correct legal phrase. 32 of 63

17 Evaluate risk (The ALARP Principle) The definition set out by the Court of Appeal (in its judgment in Edwards v. National Coal Board, [1949] 1 All ER 743) in the UK is: Reasonably practicable is a narrower term than physically possible a computation must be made by the owner in which the quantum of risk is placed on one scale and the sacrifice involved in the measures necessary for averting the risk (whether in money, time or trouble) is placed in the other, and that, if it be shown that there is a gross disproportion between them the risk being insignificant in relation to the sacrifice the defendants discharge the onus on them. 33 of 63 Evaluate risk (The ALARP Principle) In essence, making sure a risk has been reduced ALARP is about weighing the risk against the sacrifice needed to further reduce it. The decision is weighted in favour of health and safety because the presumption is that the dutyholder should implement the risk reduction measure. To avoid having to make this sacrifice, the dutyholder must be able to show that it would be grossly disproportionate to the benefits of risk reduction that would be achieved. 34 of 63

18 Evaluate risk (The ALARP Principle) The process is thus not one of balancing the costs and benefits of measures but, rather, of adopting measures except where they are ruled out because they involve grossly disproportionate sacrifices. Extreme examples might be: To spend 1m to prevent five staff suffering bruised knees is obviously grossly disproportionate; but To spend 1m to prevent a major explosion capable of killing 150 people is obviously proportionate. 35 of 63 Evaluate risk (The ALARP Principle) In reality many decisions about risk and the controls that achieve ALARP are not so obvious. Factors come into play such as ongoing costs set against remote chances of one-off events, or daily expense and supervision time required to ensure that, for example, employees wear ear defenders set against a chance of developing hearing loss at some time in the future. It requires judgment. There is no simple formula for computing what is ALARP. 36 of 63

19 Treat risk Risk treatment involves identifying the range of options for treating risks, assessing these options and the preparation and implementation of treatment plans. The approach and mood in treating risks with positive outcomes will be slightly different from that treating risks with negative outcomes. It should be noted that zero risk does not exist. 37 of 63 Options for treatment of risk with positive outcomes Actively seeking an opportunity by deciding to start or continue with an activity likely to create or maintain it (where practicable). Inappropriate pursuit of opportunities without consideration of potential negative outcomes may compromise other opportunities as well as resulting in unnecessary loss. Changing the likelihood of the opportunity, to enhance the likelihood of beneficial outcomes. Changing the consequences, to increase the extent of the gains. 38 of 63

20 Options for treatment of risk with positive outcomes (cont.) Sharing the opportunity. Another party or parties bearing or sharing some part of the positive outcomes of the risk, usually by providing additional capabilities or resources that increases the likelihood or consequence of the opportunity arising. Contracts, partnerships, joint ventures, royalty, farm-in arrangements. Usually involve sharing some of the costs involved. Often introduce new risks, in that the other party or praties may not deliver. Retaining the residual opportunity. No specific immediate action required. 39 of 63 Options for treatment of risk with negative outcomes Avoiding the risk by deciding not to start or continue with the activity that gives risk to the risk (where practicable). Risk avoidance can occur inappropriately if individuals or organisations are unnecessarily risk-averse. Inappropriate risk avoidance may increase the significance of other risks or may lead to the loss of opportunities for gain. Changing the likelihood of the risk, to enhance the likelihood of the negative outcomes. Changing the consequences, to reduce the extent of the losses. Reduction of inventory or implement continuity plans (business resilience). 40 of 63

21 Options for treatment of risk with negative outcomes (cont.) Sharing the risk. Another party or parties bearing or sharing some part of the risk, usually by mutual consent. Contracts, insurance arrangements, partnerships, joint ventures. Usually involve sharing some of the costs involved, such as premium paid for insurance. Acquire a new risk in that the other party or praties to which risk has been transferred may not manage the risk effectively. Retaining the residual risk. Risk can also be retained by default, e.g. when there is a failure to identify or appropriately share or otherwise treat risk. 41 of 63 Semi-quantitative risk assessment methods Semi-quantitative methods are used to determine the relative hazards associated with unwanted outcomes. They include: Indexing methods Point schemes (fire risk ranking) 42 of 63

22 Indexing methods Fire risk indexing or ranking, also called schedule, may be defined as a systematic combination of pertinent fire protection factors. Basic assumption relatively small number of factors account for most of the problems of fire protection. The methods require fire protection factors be measurable. Both identification of pertinent factors and method of combination require consideration of an acceptable level of risk as the goal for achievement. 43 of 63 Indexing methods (Insurance rating) Insurance rating defined as an empirical standard for the measurement of relative quantity of fire hazard. Take into consideration various items contributing to perils of fire, including construction and occupancy, with a view to determining which features either enhance or minimise the probability of loss. Credits and charges representing departures from standard conditions are incorporated in the schedules. The schedule rate is typically the sum of all charges minus the sum of all credits, and constitutes a standard for the measurement of the fire risk. 44 of 63

23 Indexing methods (Insurance rating) The US ISO (Insurance Services Office) commercial fire rating schedule includes estimation of percentage charges, the basic building grade, and related loss experience. For each building, a percentage occupancy charge is determined from tabulated charges for classes of occupancy but modified by factors such as the specific hazards of a particular occupancy. The building is graded by its resistance to fire by structural walls and floors and roof assemblies. The premium is the product of occupancy charges and building grade modified by factors such as potential exposure to external fires, and fire protection systems provided internally. Insurance rating uses reported fire loss data and compensations paid in the past to determine future premium. 45 of 63 Indexing methods (Dow Fire and Explosion Index) Developed by Dow Chemical Company to identify areas with significant loss potential. Original edition (1964) a modified version of the Chemical Occupancy Classification rating system developed by Factory Mutual prior to Subsequently improved, enhanced, and simplified. Currently 7 th edition (1994). Provide a direct and logical approach for determining the probable risk exposure of a process plant, and to suggest approaches to fire protection and loss prevention design. 46 of 63

24 47 of 63 Point schemes (Gretener( method) A different method developed in Switzerland during the 1960s and 1970s that considers fire risk as the product of hazard probability and hazard severity. Fire risk is measured as the ratio of negative features that increase risk to positive features that decrease risk. R = (P A) / (N S F) R = Fire risk P = Potential hazard A = Activation (ignition) hazard N = Normal protection measures S = Special protection measures F = Fire resistance of the structure 48 of 63

25 Point schemes (Fire Safety Evaluation System) The FSES is a schedule approach to determining equivalencies to the NFPA 101 Life Safety Code for certain types of occupancies, and provides a uniform method for evaluation. The FSES subdivides a building into fire zones for evaluation. A fire zone is defined as a space separated by floors, fire barriers or smoke barriers. In application, every zone in the building should be evaluated. Where repetition occurs, a typical zone can be evaluated. 49 of 63 Point schemes (Fire Safety Evaluation System) The FSES utilises the risk concept in that several parameters are considered as occupancy risk, e.g. in health care facilities, parameters identified include patient mobility, patient density, zone location, ratio of patients to attendants, and average age of patients. Values for these parameters, all others in the FSES, were determined on the basis of the experienced judgment of a group of fire safety professionals and represent the opinions of that panel of experts. There is no documented process for validating or revising the values, and there is no attempt to directly correlate the fire safety parameters with the risk parameters. 50 of 63

26 Point schemes (Fire Safety Evaluation System) Safety features must offset the calculated occupancy risk. The FSES uses 13 fire safety parameters with up to seven levels of safety for each parameter. FSES considers redundancy through simultaneous use of alternative fire safety strategies, namely (1) containment, (2) extinguishment, and (3) people movement. The purpose is to ensure that failure of a single protection system will not result in a major fire loss. Evaluation of equivalency is carried out by comparing the calculated level for each fire safety strategy with the stated minimum values that range from 100% to 12% of those for new buildings. 51 of 63 Point schemes (Fire Safety Evaluation System) Determination of parameter values is commonly carried out via a formal process called Delphi exercise. Delphi is a non-interactive group judgment method for reaching consensus in decision making. The process involves a panel of experts who are asked to estimate otherwise unpredictable relationships of system variables. Traditionally the panel members do not meet; this is designed to eliminate elements of group dynamics that are personality dependent and may be undesirable in making a technical decision, such as dominant individuals, irrelevant communication, and pressures to conform. 52 of 63

27 Point schemes (Fire Safety Evaluation System) The FSES concept has been proposed to be applied to existing buildings in HK to determine the fire safety level (index), and from the index, to rank improvements by priority. 53 of of 63

28 Issues with point schemes Point schemes do not have predictability; the differences in the scores resulting from different provisions do not bear relationship with the degree of improvement of the environment afforded by the provisions. They could not provide an explanation to the physics and chemistry that is manifested, as the numerical values of the attributes and the weightings attached to the attributes are typically based on past history and statistics but completely detached from physics and chemistry. 55 of 63 Issues with point schemes Variations in performance among different fire safety system components are typically not reflected in point schemes. Generally, scores in point schemes are not provided with error limits but possess single values, i.e. any uncertainties in the statistical data or judgment on which the scores are based are ignored. 56 of 63

29 Determine values of human life Gross output Based on goods and services which a person can produce if not denied, by death, of the opportunity to do so. Since the community as a whole consumes most of what it produces, it is argued that when a person dies, it also saves concurrent future consumption. Hence this approach usually gives a small value for life, especially when discounted consumption is deduced from discounted production. 57 of 63 Determine values of human life Livelihood approach Assigns valuations in direct proportion to income and is similar to the output approach. The present value of future income of an individual is estimated and reduced by an amount equal to discounted consumption. This method normally favours males over females, working persons over the retired, and higher paid over lower paid persons in a way that may not reflect individual or social preferences. 58 of 63

30 Determine values of human life Insurance method Assumes the value of life equal to the life insurance policy value. This method has two drawbacks. Firstly a decision on whether or not to purchase insurance and the amount of insurance largely depends on how much the individual is willing and capable to afford. Secondly the purchase of an insurance policy does not reduce the mortality risk to an individual and hence insuring life is not exactly a value trade-off that is considered between mortality risks and costs. 59 of 63 Determine values of human life Court awards Compensations demanded by the court (lawyers and judge) from a party considered to be responsible for the fatality to pay to heirs of the deceased. There were no consistencies on the ruling from the courts as some courts include a subjective component for pain and suffering of survivors but some courts do not. Where injuries are involved, people who suffer severe personal injury qualify for substantial damages for subjective losses than in fatal cases. Some courts also have limited to very low levels the damages that may be awarded for reductions of life expectancy. 60 of 63

31 Determine values of human life Willingness to pay Based on the money people are willing to spend to increase their safety to a level they prepare to accept. A widely adopted method. This approach treats safety as a commodity like any other. The amount people are prepared to pay to reduce a given risk will depend on the total level of risk, the 'immediacy' of risk, the knowledge about the risk, the amount already being spent on safety, and the earnings of the individuals. 61 of 63 Determine values of human life All five methods mentioned above have considerable variabilities and subjectiveness. Values placed on life as estimated by different methods were reported by Ramachandran to range from US$25,000 to US$60M. Because of the uncertainly on value estimation of human life and in order to avoid ethical, moral and political debate, some risk analysts prefer to use relative, quantitative risk to life parameters that are not expressed in financial terms. 62 of 63

32 Q & A Thank You for Your Attention 63 of 63