Risk evaluation methods. Checklists and points systems as elementary fire risk assessments. Checklists are not well suited for risk quantification. Just think of a workplace which complies with 18 of 20 fire safety items, but fails to comply with the code requirements for the electrical installation and for the use of flammable liquids: The 18/20 score does not mean a "good risk". Some British checklists are therefore complemented by weighing factors to obtain some kind of risk classification in a point system, with or without a benchmark for satisfactory performance. Ranking methods or linear fire risk assessments. The FiRE- tECH WG6 report describes ranking methods as follows: "Ranking methods or semi-quantitative methods are used in a wide range of applications. These methods have often been developed with the purpose of simplifying the risk assessment process for a specific type of building, process etc.   Ranking methods remove most of the responsibility from the user to the producer of the method. The user of a ranking method remains responsible of the data gathering but the producer of the method has narrowed his freedom of quantification. In general, a group of experts first had to identify every single factor that affects the level of safety or risk, which represents positive features (increase the level of safety) and negative features (decrease the level of safety). The importance of each factor has to be decided by assigning a value. This value is based on the knowledge and the experience of experts over a long time coming from insurance, fire brigade, fire consultants, scientists etc. Assigned values are then operated by some combination of arithmetic functions to achieve a single value. The value can be called as "risk index" and is a measure of the level of safety/risk in the object and it is possible to compare this to other similar objects and to a stipulated minimum value.   Not all ranking methods include a basic level for a satisfactory protection, but give only a relative position as situation A is better/ worse/ equivalent to situation B. This can be an advantage for the user which can define his own level of protection, but in practice, most inexperienced users want that an expert system gives them a clue on "what is good enough".   An advantage of fire ranking methods is their simplicity, they are considered as very cost effective tools. Another advantage of this method is the structured way in which the decision making is treated. This facilitates understanding of the system for persons not involved in the development process and makes it easier to implement new knowledge and technology into the system. Ranking systems have their disadvantages too. They are usually linked to a specific type of occupancy, so that they can only be used for a limited group of buildings. If they are linked to national code requirements, they will not be applicable for similar risks in other countries. I wish to draw attention to an ethical issue connected to this type of code linked systems like the NFPA 101A Fire Safety Evaluation System. This method uses a different (lower) benchmark for existing and for new buildings. This is based on the legal situation that backward application of new standards is not accepted. But, should the fire protection engineer design for less if he has the tools to design for equivalent levels of safety in new buildings and existing buildings? Some ranking systems, e.g. the weighing and grading system proposed by FiRE-tECH WG8, enter the stakeholders' appreciation in the calculation, which may result in a recommendation they want to receive, different from what they ought to hear from a professional adviser. The WG6 report had the FRAME and Gretener methods classified as point systems, but this does not justice to these methods. Point and ranking systems combine the weighed parameters in a SUM, where FRAME (and Gretener) combine weighed factors in a PRODUCT, which puts them in the category of probability based quantification methods. Probability based risk quantification methods. Probability based methods start from the observation that unwanted vents like fire have a variety of outcomes. Most methods are not specifically developed for fire risks and need some kind of interpretation to be used for fire risk assessments. The existing methods can be classified as two-dimensional or three-dimensional evaluation of risks.   Two-dimensional methods were developed by the nuclear, chemical and aviation industry where the hazard exposure is continuous or exists over long periods. They express the risk as a combination of a probability of occurrence or frequency and a magnitude of the consequent loss or severity.   Three-dimensional methods use Exposure, Probability and Severity for risk quantification. This type of risk evaluation is practised in those areas where the exposure to the hazard is not continuous, such as workplace risks, machinery defects, and fire. It should be noted that the severity, probability and exposure are linked to the same undesirable event. Both types often use a product or a sum of products of the risk dimensions to obtain a single risk value, which can then be used in comparisons between protection alternatives of in relation with a benchmark value.   Two-dimensional risk assessments. The "American school" of fire protection engineers uses mostly two-dimensional risk quantification schemes, based on the technique described in NFPA 551, Guide for the Evaluation of Fire Risk Assessments. A simple two-dimensional method is the risk profile, a graphical method where different levels of probability and severity are given on a x/y graph. This method is usually based on U.S. MIL-STD- 1629A, "Procedures for performing a Failure Mode, Effects and Criticality Analysis" which indicates severity levels from Minor to Catastrophic, and probability levels from Frequent to Extremely Unlikely. Each identified risk will be shown by a point on the risk profile. On that graph profile, three distinct zones can be defined: The green zone shows the acceptable risks with a low value for the product severity * probability, the red zone the unacceptable risks and the yellow zone those risks that give concern for corrective action. An other two-dimensional risk assessment method is the ETA or event tree analysis. The outcome of a hazardous event often depends on more than one condition. This can be visualised and explained with event networks or event trees, which show the cause, effect and interaction between various events. An event tree is a graphical logic model that identifies and quantifies possible outcomes following an initiating event. The tree structure is organized on a time scale. Probabilities can be calculated from the tree, and consequences are typically assigned to the end states but may cumulate along the tree. In an ETA, the analyst has full control of input and output, which means that any ETA needs an external check by an equally expert person or organisation as the analyst. Solving fire risk problems with ETA techniques do require professional skills in fire modelling and risk analysis. If this skill is not available in the organisation, external assistance is appropriate. The Canadian FiRECAM™ (Fire Risk Evaluation and Cost Assessment Model) is a computer program that makes a combination of fire modelling and ETA. To undertake the evaluation of life risks and fire costs, FiRECAM simulates for six design fires the ignition of a fire in various locations in a building, the development of the fire, smoke and fire spread, occupant response and evacuation, and fire department response. These calculations are performed by nine sub-models interacting with each other in a loop. The outcome of the FiRECAM calculation is an Expected Risk to Life (ERL) of the occupants, defined as the expected number of deaths over the design life of a building, divided by the population of the building and the design life of the building. For the property risk FiRECAM uses a Fire Cost Expectation (FCE) defined as the expected total fire cost which is the sum of capital costs of the passive and active fire protection systems , Maintenance cost of the active fire protection systems and expected losses as a result of all probable fire spread in the building , divided by the cost of the building and its contents. The FiRECAM program includes a visual representation of the building and graphical reports, but gives no clear answer to the basic question: "is it good enough?" It is limited The fact that the program is based on Canadian data, including response time for fire services and building costs, is appreciated in Canada, but is a major drawback for its use outside the Canadian market. For property damage assessments, the probability and severity combination is preferred by the stakeholders, as they will need to compare the investment costs for protection with the expected cost of risk during the useful life of the building.   For life safety, a combination of severity and exposure is more often used in the risk assessments which are presented to the AHJ for the approval of a design which is not made according to the prescriptive fire codes. For these risk assessments, fire growth and evacuation modelling software is often combined.   The fire protection community has spent a lot of efforts in the development of such software. The international survey of computer models made in 2002 by Olenick and Carpenter mentioned almost 50 zone models, 18 fields models and some 20 egress models, but only a few risk assessment models. Three-dimensional risk assessments  Methods based on a combined evaluation of exposure, probability and severity offer a better approach for fire, which is a non- continuous hazard and basically a rare but unwanted event. This approach fits better to the intuitive way of making fire risk assessments and to the reasoning underneath code requirements. One of the oldest and widespread methods for workplace risk assessment was developed back in 1976 by Kinney, Wiruth e.a. and is widely used for the analysis of workplace hazards. The approach is known as the Kinney or ESP method. A similar approach can be found in the standards for the safety of machinery, such as EN-ISO 14121-1:2007 and the older EN 1050 and EN 954-1 standards.  The Kinney or ESP-method Kinney uses 3 non linear numerical scales for severity, probability and exposure. The proposed values for each factor are situated on a non-linear (semi-logarithmic) scale, and the calculated risk factor is compared with the following "decision table". The non-linear scale represents the risk aversion phenomenon, i.e. the human attitude to reject high severity / low probability risks more than low severity / high probability risks. A decision table categorizes the identified risks and allows establishing an priority program for risk reduction. The result can be visualised as a three-dimensional parabolic field; all risks located below this limit being acceptable, those above need correction. The safety of machinery standards.  In the EN1050 and EN954-1 standards for safety of machinery severity, probability of occurrence and exposure are used to define the level of protection needed to obtain an acceptable risk level. The EN 1050 standard has been replaced recently by the EN-ISO 14121-1:2007 and the EN 954-1 by the ISO 13849-1, but the principles remain valid and can be also used to evaluate fire risks with some modifications.  The EN1050 defines the decision process which leads to 5 risk classes, based on the 3 characteristics of the unprotected risk: The EN 954-1 norm defines five levels of protection (B, 1, 2, 3, 4), related to 5 risk classes, related to 3 characteristics of the unprotected risk. These requirements are founded on a number of axioms and principles: The probability of occurrence of the danger is more or less constant: The majority of the machines is conceived for a certain lifetime and has thus a built-in failure probability. The reliability of system elements will be improved by tests, overseeing, and "fail-safe" design. One can differentiate the situation when the victim can escape or not from the risk. A fast warning is essential. If the protection is reliable, the real occurrence of the accident will be reduced. Protections (safety systems) can be made reliable by checks, self-surveillance and redundancies.   An important remark is that protection is only the second defence, prevention is always first. The duty of preventing risks is a priority. Risks must be reduced at the source and dangerous situations replaced where possible by more safe situations. The application of the general prevention principle means in practice that the residual risk will be found in the lower classes, which require less elaborate protection measures. Classifying risks and protections in 5 classes and 5 categories is a mere decision tool. In practice, there is a wide variation of possible damage and a large spectrum of available protection systems. The variety of influence factors is so large that a more gradual approach of risks and protections is advisable. It is this detailed evaluation of a large number of factors that makes the FRAME attractive for fire risk assessment. Risk communication. The output of a risk assessment has to be communicated to the stakeholders in a way they can reach informed decisions. Ranking systems with a benchmark, like NFPA 101A FSES, are therefore much appreciated by the inexperienced observer. The outcome of an ETA can also be presented in a risk profile or matrix. The fire risks located in the lower left corner (green area) are below the average frequency / severity and are considered acceptable, where those in the upper right corner (red area) are certainly unacceptably high. The weakness of such a risk matrix is that extremely severe incidents with a very low frequency can remain unnoticed, as they are located nearly on the x-axis of the diagram. The ETA itself will not yield any decisions. The stakeholders will have to decide on the extent of the green and red zones on the distribution diagram, or select a benchmark to define an acceptable risk. The national fire death rate can e.g. be the proposed reference. Probability and severity combinations, like 5.10-6 deaths / million hours are understandable by scientists but mean very little for decision makers, unless compared with some benchmark, e.g. national averages. A loss potential calculation in thousands of Euros or dollars will not ring a bell for an insurance broker, but a correspondingly high fire insurance premium rate will do. Some models like FiRECAM include a fire cost estimate; This looks interesting but is debatable. The cost of fire protection measures will vary considerable whether applied for new projects or for renovation or upgrades of existing buildings. Material and labour costs vary also from one region to another, and variations in inflation, finance and insurance costs will further increase the variance fork of the estimates. The result of the assessment becomes very sensitive to the input data used.  The cost estimate becomes even more complicated when the costs are unevenly distributed among the interested parties. A particular complex situation is e.g. a large warehouse where the owner of the building, the owner(s) of the content and the user of the building are different companies, with competing interests.   A loss potential calculation is therefore more useful. The FRAME benchmark " In a well protected building, the 3 risk valuse shall equal or less than 1" is easily understood by all stakeholders. For those wanting more specific knowledge, the FRAME results can be transformed into a) a fire loss estimate as % of the compartment; b) an insurance premium rate; and c) a relative probability of victims, compared to a residential fire risk. Most managers are happy with this kind of information that is easily understandable and still gives them the freedom of decision making. Authorities do not like risk assessment results that can twist their arm for an "automatic grant" of a permit or approval of equivalency, so it is almost impossible to obtain a straightforward official approval of FRAME or of any other risk assessment method. PRINT  THIS SECTION  (pdf)