13 commonly used methods for safety assessment

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There are many methods for safety assessment. Here, 13 commonly used safety assessment methods are introduced for everyone to choose from in practical applications. 　　1 Safety Review Method The safety review method can be considered the first safety assessment technique; it is sometimes also referred to as a process safety review, or a “design review” and a “loss prevention review”. It can be used at any stage of a construction project. When evaluating existing installations (operational installations), traditional safety inspections mainly include visual inspections, regular routine inspections, or safety checks. (For example, if the process is still in the design phase, the design team can review a set of drawings. ) The purpose of safety inspection methods is to identify device conditions or operating procedures that may lead to accidents, injuries, significant property losses, or have a major impact on the public environment. General safety inspectors mainly include personnel related to the equipment, namely operators, maintenance workers, engineers, managers, safety officers, etc., depending on the organizational structure of the factory. 　　The purpose of safety inspections is to improve the safe operation of the entire installation, rather than interfering with normal operations or punishing any issues that are identified. After completing the safety inspection, the evaluators should propose specific measures and recommendations for areas that require urgent improvement. 　　2 Safety Checklist Method (Safety Checklist Analysis, SCA) To identify potential hazards and harmful factors in various equipment, facilities, materials, workpieces, operations, as well as management and organizational measures within a project or system, the subject of inspection is first broken down into smaller subsystems. By using questions or scoring systems, each item on the checklist is examined one by one to ensure nothing is overlooked; such a checklist is known as a safety checklist. 　　3 Risk Rank Method (RR) The Risk Rank method is an evaluation technique. Through comparative calculations by evaluators regarding the current status and inherent characteristics of several processes (identifying the hazards of different work sites based on the degree of hazard, probability of accidents, and severity of accidents at those sites), the relative importance of the process hazard characteristics is determined. Based on these evaluation results, the objects for further evaluation are identified. 　　The hazard index evaluation can be applied at various stages of engineering projects (feasibility studies, design, operation, etc.), either before the completion of a detailed design plan or prior to the formulation of a hazard analysis plan for existing installations. Of course, it can also be used for existing installations as a basis for determining process and operational hazards. 　　Several hazard rating methods are currently in wide use. 　　This method can be used in various ways, ranging from simple to complex; it is capable of both qualitative and quantitative analysis. For example, evaluators can perform a simple classification of the site based on a qualitative assessment of the degree of hazard at the workplace, the likelihood of accidents, and their severity. Alternatively, in a more complex approach, certain numerical values are assigned to various process characteristics to create a numerical chart; this chart can then be used to calculate quantitative classification factors. Common evaluation methods include: ① Hazard assessment; ② Dow Chemical’s Fire and Explosion Index method; ③ Mond method; ④ Hazard level index method for chemical plants; ⑤ Other hazard level evaluation methods. 　　4 Preliminary Hazard Analysis (PHA)
Preliminary Hazard Analysis is a method originating from the safety program requirements stipulated in U.S. military standards. It is primarily used for analyzing critical areas related to hazardous substances and devices, including before design, construction, and production. First, it analyzes the types of hazards present in the system, the conditions under which they arise, and the consequences that can lead to accidents. The purpose is to identify potential hazards within the system, determine their risk levels, and prevent these hazards from developing into accidents. 　　Preliminary hazard analysis can achieve the following 4 objectives: ① Generally identify the main hazards associated with the system; ② Determine the causes of these hazards; ③ Predict the impact of accidents on personnel and the system; ④ Assess the level of risk and propose measures to eliminate or control it. 　　The pre-hazard analysis method is typically used in the initial stages of process projects where little is known about potential hazards and these cannot be detected through experience. It is commonly used in preliminary design or R&D (research and development) of process plants; when analyzing a large existing plant or when the environment does not permit the use of more systematic methods, the PHA method is often given priority. 　　5 Fault Hypothesis Analysis Method (What…If, W1) The fault hypothesis analysis method is a creative analysis technique for system processes or operational procedures. Those using this method should be familiar with the process, and by asking questions (fault hypotheses), they can identify potential accident risks (in fact, in a hypothetical system, once a serious accident occurs, identifying the underlying factors that contributed to it; under the worst-case conditions, these are the possibilities that could lead to an accident). 　　Unlike other methods, it requires evaluators to understand the basic concepts and apply them to specific problems. There is very little information available on fault hypothesis analysis methods and their applications, yet it can be frequently used at various stages of project development. 　　The fault hypothesis analysis method generally requires evaluators to start by using “What…if” when considering relevant issues. Any issue related to process safety, even if it is not directly related, can be raised for discussion. For example: · What to do if the wrong raw materials are provided? · What to do if the pump stops operating during operation? · What to do if the operator opens valve B instead of valve A? Generally, all problems are recorded and then categorized, for example, by issues such as electrical safety, fire safety, and personnel safety, so that they can be discussed separately. For operational units that are currently in use, conversations are held with the operators, and the questions raised take into account any abnormal production conditions related to the unit, not just equipment failures or changes in process parameters. 　　6 Fault Hypothesis Analysis/Checklist Analysis Method (What…If/Checklist Analysis, W1/CA) The fault hypothesis analysis method/checklist analysis method is a combination of a creative hypothesis analysis approach and a safety checklist analysis approach, which compensates for the shortcomings of each when used alone. 　　For example, the safety checklist analysis method is an experience-based approach; when using it for safety assessment, success depends to a large extent on the experience level of the person who prepares the checklist. If the checklist is incomplete, it is difficult for evaluators to conduct an effective analysis of the hazardous conditions. The fault assumption analysis method encourages evaluators to consider potential accidents and their consequences; it compensates for any lack of experience that may exist when preparing checklists. Conversely, the checklist aspect makes the fault assumption analysis method more systematic. 　　Fault hypothesis analysis/checklist analysis methods can be used at any stage of a process project. 　　Similar to most other evaluation methods, this method also requires personnel with extensive process experience to carry out; it is commonly used to analyze the most common hazards present in a process. Although it can also be used to evaluate potential accident hazards at all levels, fault hypothesis analysis/checklist analysis is generally primarily used for a preliminary analysis of process hazards, after which other methods can be employed for a more detailed evaluation. 　　7 Hazard and Operability Study (HAZOP) HAZOP is a qualitative safety assessment method. Its basic process involves using guiding words to identify changes in the process conditions (i.e., deviations), and then analyzing the causes, consequences of these deviations as well as possible countermeasures. 　　Hazard and operability study techniques are based on the principle that experts from diverse backgrounds, when working together, can influence and inspire one another in terms of creativity, systematicness, and style, enabling them to identify and discern more problems – making this approach more effective than working independently and submitting individual results. Although hazard and operability study techniques were initially developed specifically to evaluate new designs and processes, they can also be applied at various stages of the entire life cycle of engineering and system projects. 　　The essence of Hazard and Operability Analysis is to analyze process flow diagrams and operating procedures through a series of meetings; various professionals carry out process hazard and operability studies on conditions that deviate from the design specifications using established methods. Imperial Chemical Industries (ICI, UK) was the first company to determine that hazard and operability studies should be conducted by a team composed of members from different fields. Given this, although an individual might use the hazard and operability analysis method on their own, it can by no means be called hazard and operability analysis. Therefore, the key difference between hazard and operability analysis techniques and other safety evaluation methods is that the latter can be carried out by a single person, whereas hazard and operability analysis must be performed by a multidisciplinary team of skilled professionals. 　　8 Failure Mode Effects Analysis (FMEA) Failure Mode Effects Analysis (FMEA) is a method in systems safety engineering. It involves dividing a system into subsystems, devices, and components based on their characteristics, splitting the system as needed, and then analyzing the possible failure modes that may occur in each part along with their impacts, so that appropriate measures can be taken to enhance the system’s safety and reliability. 　　(1) Fault. Components, subsystems, and systems fail to meet the requirements specified in their design during operation, as a result of which they are unable to complete the assigned tasks or do so inadequately. 　　(2) Fault type. Each type of failure that occurs in a system, subsystem, or component is called a failure mode. For example: a valve failure can have 4 types of faults, namely internal leakage, external leakage, inability to open, and inability to close properly. 　　(3) Fault level. The levels classified according to the degree of impact that different types of faults have on the system or subsystems are known as fault levels. 　　List all types of equipment failures and their effects on a system or device. These failure modes describe equipment malfunctions (turning on, turning off, leaking, etc.). The impact of each failure type is determined by its systematic effect on the equipment’s operation. FMEA identification identifies single failure modes that can directly cause an accident or have a significant impact on it. In FMEA, human factors are not determined directly, but the impact of human error is usually represented as a equipment failure mode. An FMEA cannot effectively identify the exhaustive combinations of equipment failures that lead to an accident. 　　9 Fault Tree Analysis (FTA) A fault tree is a directed “tree” that describes the causal relationships of accidents; it is one of the important analysis methods in safety systems engineering. It can identify and evaluate the hazards of various systems; it is suitable for both qualitative and quantitative analysis. It is characterized by simplicity and vividness, reflecting the systematicness, accuracy, and predictability of studying safety issues using systems engineering methods. As an advanced scientific method for safety analysis and evaluation as well as accident prediction, FTA has been recognized and widely adopted both domestically and internationally. 　　In the early 1960s, Bell Telephone Laboratories in the United States began developing fault trees to study the safety issues of militia-style missile launch control systems, contributing to the solution of problems related to predicting accidental events in missile systems. Subsequently, Boeing’s researchers further developed the FTA method to apply it in the aerospace industry. In the mid-1960s, FTA expanded from the aerospace industry to other industrial sectors centered around the nuclear energy industry. In 1974, the U.S. Atomic Energy Commission published a report on the assessment of catastrophic risks associated with nuclear power plants – the Larson Report – in which FTA was used extensively and effectively, drawing widespread attention around the world. Today, this method is employed in many industrial sectors. 　　FTA can not only identify the direct causes of an accident but also uncover its underlying causes; therefore, it can be used to assess the safety of engineering or equipment designs, during accident investigations, or when developing new operating procedures. Japan’s Ministry of Labor actively promotes the FTA method and requires safety officers to learn how to use it. 　　Since 1978, our country has begun research and the application of FTAs. Practice has shown that FTA is suitable for China’s national conditions, and it should be widely promoted and adopted in the country. 　　10 Event Tree Analysis (ETA)
Event Tree Analysis is used to analyze the likelihood of accidents occurring as a result of common equipment failures or process fluctuations (referred to as initial events). 　　Accidents are the result of typical equipment failures or process abnormalities (referred to as initial events). Unlike fault tree analysis, event tree analysis uses induction (rather than deduction). Event trees provide a systematic way to document the consequences of an accident, and can determine the relationship between the events leading to those consequences and the initial event. 　　Event tree analysis is suitable for analyzing initial events that lead to different consequences. The event tree focuses on the initial causes that may lead to an accident and the impact of those initial events on the consequences of the accident. Each branch of the event tree represents an independent sequence of accidents; for a given initial event, each such independent sequence clearly defines the functional relationships between the safety functions. 　11 Human Reliability Analysis (HRA) Human reliability is a necessary condition for the success of human-machine systems, and human behavior is influenced by many factors. These “performance influencing factors” (PSFs) can be intrinsic human attributes, such as tension, emotions, upbringing, and experience; they can also be external factors, such as the workplace, environment, actions of supervisors, procedural rules, and hardware interfaces. There are countless PSFs that influence human behavior. Although some PSFs cannot be controlled, many can be controlled and have a significant impact on the success or failure of a process or operation. 　　For example, evaluators can incorporate human error into the fault tree. A “what-if”/checklist analysis can take this scenario into account—that under abnormal conditions, an operator might open a valve that should have remained closed. Typical Hazard and Operability Studies (HAZOP) also consider operator errors as causes of process deviations. Although these safety evaluation techniques can be used to identify common human errors, they still focus primarily on the hardware aspects that cause accidents. When there is a lot of manual operation in the manufacturing process, or when the human-machine interface is complex and it is difficult to assess human errors using standard safety evaluation techniques, specific methods are needed to evaluate these human factors. 　　Human factors is the discipline that studies machine design, operation, working environments, and how they harmonize with human abilities, limitations, and needs. There are many different methods available for human factors experts to use to evaluate work conditions. A commonly used method is called Job Safety Analysis (JSA), but this method focuses on the personal safety of the workers. JSA is a good starting point, but for process safety analysis, human reliability analysis methods are more useful. Human reliability analysis techniques can be used to identify and improve PSFs, thereby reducing the likelihood of human errors. This type of technical analysis examines the characteristics of systems, processes, and operators to identify the sources of errors. 　　Using HRA technology in isolation, without combining it with an analysis of the entire system, seems to emphasize human behavior too much while ignoring the impact of equipment characteristics. If the aforementioned system is one known to be prone to accidents caused by human error, it would be inappropriate to do so. Therefore, in most cases, it is recommended to use the HRA method in combination with other safety assessment methods. Generally, HRA technology should be used after other evaluation techniques (such as HAZOP, FMEA, FTA) to identify specific human errors with serious consequences. 　　12 Job Risk Analysis (LEC) Kenneth.J.Graham and Gilbert.F.Kinney from the United States studied the risks associated with working in environments that pose potential dangers. They proposed a formula based on a comparison between the environment under evaluation and certain reference environments, taking the risk level of the working conditions as the dependent variable (D), while the likelihood of accidents or hazardous incidents (L), the frequency of exposure to the dangerous environment, and the severity of the danger (C) served as the independent variables. Based on practical experience, they provided score values for various combinations of the 3 independent variables. This method involves \"rating\" the object under evaluation according to those conditions, then calculating its risk score using a formula; subsequently, the level of risk is determined by referring to a scale or chart that classifies risk levels based on these calculated scores. This is a simple and easy method for assessing the hazard of working conditions. 　　13 Quantitative Risk Assessment Method (Quantity Risk Analysis, QRA) In hazard identification and analysis, qualitative and semi-quantitative assessments are very valuable. However, these methods are of a qualitative nature only and fail to provide sufficient quantification; in particular, they cannot offer a basis for decision-making or adequate information regarding complex industrial processes that involve multiple hazards. In such cases, it is necessary to have complete quantitative calculations and assessments available. Quantitative risk assessment can fully quantify the magnitude of risks; a risk can be characterized as the product of the frequency of an accident occurring and its consequences. QRA evaluates both of these aspects and provides sufficient information to offer owners, investors, and **managers a solid quantitative basis for making informed decisions. 　　There are numerous research achievements both domestically and internationally regarding the simulation analysis of accident consequences; in developed countries such as the United States, the United Kingdom, and Germany, a series of large-scale field leakage and dispersion experiments represented by Burro, Coyote, and Thorney Island were conducted as early as the early 1980s. In the 1990s, field experimental studies were conducted on the leakage and dispersion of toxic substances. To date, hundreds of accident consequence models have been developed, such as the well-known DEGADIS, ALOHA, SLAB, TRACE, ARCHIE, etc. The practical application of accident models has also seen development. For instance, DNV’s SAFETY II software is a versatile quantitative risk analysis and hazard assessment package that includes various accident models. It can be used for plant site selection, regional and land-use decisions, selection of transportation schemes, optimized design, and ensuring acceptable safety standards. The simulation software offered by Shell Global Solutions, namely Shell FRED, Shell SCOPE, and Shell Shepherd, are risk assessment tools for hazards such as leaks, fires, explosions, and dispersion. These software programs are based on mathematical models derived from numerous experiments, and thus possess a high degree of reliability. The results of the assessment are presented in numerical or graphical form to show the affected areas of the accident, as well as the risks borne by individuals and society. Accidents that may occur can be classified according to the severity of the risks, which helps in formulating measures to reduce those risks.