Hazard analysis causal factors

Bow-Tie Analysis (BTA) a type of qualitative process hazard analysis.The methodology is an adaptation of three conventional system safety techniques Fault Tree Analysis, Causal Factors Charting, and Event Tree Analysis. Existing safeguards (barriers) are identified and evaluated for adequacy... 

An important principle about HA is that one particular HA type does not necessarily identify all the hazards within a system identification of hazards may take more than one analysis type, hence the seven types. A corollary to this principle is that one particular HA type does not necessarily identify all of the HCFs more than one analysis type may be required. After performing all seven of the HA types, all hazards and causal factors should have been identified, assuming an adequate analysis program was conducted. Additional hazards that were overlooked may be discovered during the test program. 

The human factors audit was part of a hazard analysis which was used to recommend the degree of automation required in blowdown situations. The results of the human factors audit were mainly in terms of major errors which could affect blowdown success likelihood, and causal factors such as procedures, training, control room design, team communications, and aspects of hardware equipment. The major emphasis of the study was on improving the human interaction with the blowdown system, whether manual or automatic. Two specific platform scenarios were investigated. One was a significant gas release in the molecular sieve module (MSM) on a relatively new platform, and the other a release in the separator module (SM) on an older generation platform. 

Once the causal factors have been identified, the factors are analyzed using a root cause analysis tool, such as 5-AVhys or predefined trees. See Chapter 9 for a more detailed discussion of Barrier Analysis (sometimes called hazard-barrier-target analysis or HBTA) and Change Analysis (also referred to as Change Evaluation/Analysis or CE/A). In essence, these tools act as a filter to limit the number of factors, which are subjected to further analysis to determine root causes. 

The design of most process plants relies on redundant safety features or layers of protection, such that multiple layers must fail before a serious incident occurs. Barrier analysis ) (also called Hazard-Barrier-Target Analysis, HBTA) can assist the identification of causal factors by identifying which safety feature(s) failed to function as desired and allowed the sequence of events to occur. These safety features or barriers are anything that is used to protect a system or person from a hazard including both physical and administrative layers of protection. The concepts of the hazard-barrier-target theory of incident causation are encompassed in this tool. (See Chapter 3.)... 

Change analysis o) (also known as Change Evaluation/Analysis, CE/A) is another tool that can assist the identification of causal factors. It is useful for brainstorming about what has changed since conditions were safe, or perceived as safe. It may also be used for hypothesizing potential contributory factors to a hazardous condition or action. 

The following are two examples of causal factors identified using STPA step 2 as potentially leading to the hazardous state (violation of the safety constraint). Neither of these examples involves component failures, but both instead result from unsafe component interactions and other more complex causes that are for the most part not identifiable by current hazard analysis methods. 

A more careful comparison has also been made. JAXA (the Japanese Space Agency) and MIT engineers compared the use of STPA on a JAXA unmanned spacecraft (HTV) to transfer cargo to the International Space Station (ISS). Because human life is potentially involved (one hazard is collision with the International Space Station), rigorous NASA hazard analysis standards using fault trees and other analyses had been employed and reviewed by NASA. In an STPA analysis of the HTV used in an evaluation of the new technique for potential use at JAXA, all of the hazard causal factors identified by the fault tree analysis were identified also by STPA [88]. As with the BMDS comparison, additional causal factors were identified by STPA alone. These additional causal factors again involved those related to more sophisticated types of errors beyond simple component failures and those related to software and human errors. 

Although some causal factors can be hypothesized early, a hazard analysis using STPA can be used to generate a more complete list of causal factors later in the development process to guide the design process after an architecture is chosen. 

If hazard identification and analysis do not relate to actual causal factors, corrective actions will be misdirected and ineffective. 

If hazard identification and analysis do not relate to actual causal factors, the resulting corrective actions proposed will be misdirected and ineffective. A superior quality of incident investigation is required to identify and evaluate actual causal factors so that appropriate corrective actions can be taken. 

A criticism of historical, after-the-fact data (of outcome statistics) is that such measures are not hazard-specific that is, they do not identify incident causal factors without additional analysis. That s so. If safety professionals want to identify hazard-specific situations that may be predictive and give direction to the actions that should be taken to reduce risk, they will have to do some analysis. 

During the operations phase, new hazards are identified by periodic inspections, worksite monitoring, audits, and appraisals. Techniques used to identify hazards during the operations phase include checklists, PET analysis, and safety studies. Accident analysis is also an important method of detecting previously undetected or uncorrected hazards. Accident analysis tools include change analysis, PET analysis, MORT and mini-MORT analysis, and event and causal factors charts. 

Organizations can use a variety of processes to analyze workplace hazards and accident causal factors. Hazard evaluations and accident trend analysis can help improve the effectiveness of established hazard controls. Routine analysis enables an organization to develop and implement appropriate controls for hazardous processes or unsafe operations. Analysis processes rely on information collected from hazard surveys, inspections, hazard reports, and accident investigations. This analysis process can provide a snapshot of hazard information. Effective analysis can then take the snapshots and create viable pictures of hazards and accident causal factors. 

Fault Tree Analysis (FTA) is a well known and widely used safety tool, implementing a deductive, top down approach. It starts with a top level hazard, which has to be known in advance and "works the way down" through all causal factors of this hazard, combined with Boolean Logic (mainly AND and OR gates). It can consider hardware, software and human errors and identifies both single and multiple points of failure. Both a quantitative and qualitative analysis is possible. 

An organization that does not encourage employee participation and involvement and does not seek the advice of employees who have experience with the work being done do not benefit from the contributions they can make with respect to hazard identification and analysis and risk reduction, and thus improved efficienqr. Failure to involve employees sometimes results in known hazardous situations to remain in existence and become incident causal factors. 

Once the hazards, including the causal factors, have been identified, it becomes important to evaluate the hazards and their effects. Most hazard analysis methodologies apply some type of severity classification. This classification is used as a marker to compare the consequences of one hazard to another. Usually some engineering analysis is done so that you can understand what the effects of the hazard would be if an accident did occur. 

Be Carefnl Do not overnse EMEAs. They are expensive to conduct if you use it across the entire system. What makes more sense is to apply it selectively, once a catastrophic or significant hazard and its causes are identified through a safety analysis (e.g., hazard analysis or HAZOP), and if one of them is component failnre, use the FMEA to further drill down to all the causal factors of the component failure that could lead to the hazard. 

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