Hazard likelihood

Severity listing of each hazard —Likelihood of each hazard... 

Hazard identification Factors for hazards Likelihood and consequences Operating conditions Risk reduction measures Assumptions... 

Likelihood is one parameter in the risk equation. Risk is the safety measure of a potential future event, stated in terms of event likelihood and event severity. Hazard likelihood is the expected likelihood that the identified hazard will be activated and becomes an actual mishap. Hazard likelihood is the estimated likelihood of a hazard transitioning from a conditional state to an actual mishap event state, resulting in an actual mishap with undesired outcome. 

In a risk assessment, hazard likelihood can be characterized in terms of probability, frequency, or qualitative criteria. Quite often, the term hazard probability is incorrectly used when the actual assessment is done in terms of frequency or qualitative criteria. This is why hazard likelihood is a more accurate term. Likelihood is a measure of how possible or likely it is that an event will occur, such as a hazard-mishap. Likelihood can typically be characterized in one of the following ways ... 

Hazard probability is typically obtained from calculations made using the HCF failure rates and the exposure time involved. It should be noted that mishap likelihood and hazard likelihood are really the same entity, just viewed from two different perspectives. 

The HRI is an index number indicating qualitatively the relative risk of a hazard. It is derived from the HRI matrix by identifying the matrix cell resulting from the intersection of the hazard likelihood and hazard severity values. In a typical HRI matrix, such as the matrix in MIL-STD-882, there are 20 cells created by a 4 x 5 matrix. The matrix cells are labeled with an index number of 1 through 20, where 1 represents the highest risk and 20 the lowest risk. The smaller the HRI number, the higher the safety risk presented by the hazard. The HRI number establishes the safety significance of a hazard and who can accept the risk for the hazard. It should be noted that the HRI is also often referred to as the mishap risk index (MRI). However, since hazard risk and mishap risk are really the same entity, then the HRI and the MRI are really the same entity, just viewed from two different perspectives. 

The HRI matrix is a risk matrix that is utilized to establish the relative (vice absolute) risk of a hazard. The matrix maps hazard severity on one axis and hazard likelihood on the other axis. Once a hazard s severity and likelihood are determined, they are mapped to a particular HRI matrix cell (the likelihood-severity intersection), which yields the HRI risk level for that hazard. The likelihood and severity axes are broken into cells defined by qualitative and semiquantitative criteria. 

Risk Assessment— This step involves determining the risk presented by each identified hazard. Analysis must be performed to assess hazard likelihood and severity. This requires knowing and understanding the HCFs and hazard effects. 

When a hazard is identified, it is very difficult to reduce the hazard severity, it is much easier to reduce the hazard likelihood. For this reason, the risk severity category almost always remains the same, even after mitigation. 

In the first step, a screening process will be applied to separate the major potential hazards these will be addressed in more detail. QRA techniques are used to evaluate the extent of the risk arising from hazards with the potential to cause major accidents, based on the prediction of the likelihood and magnitude of the event. This assessment will be based on engineering judgement and statistics of previous performance. Where necessary, risk reduction measures will be applied until the level of risk is acceptable. This of course is an emotive subject, since it implies placing a value on human life. 

Risk characterization is defined as the integration of the data and analysis of the above three components to determine the likelihood that humans wiU. experience any of the various forms of toxicity associated with a substance. When the exposure data are not available, hypothetical risk is characterized by the integration of hazard identification and dose—response evaluation data. 

Toxicity, the potential to produce harmful effects, is to be clearly differentiated from hazard, which is the likelihood that a particular material will exhibit its known toxicity under specific conditions of use. 

As microprocessor-based controls displaced hardwired electronic and pneumatic controls, the impac t on plant safety has definitely been positive. When automated procedures replace manual procedures for routine operations, the probability of human errors leading to hazardous situations is lowered. The enhanced capability for presenting information to the process operators in a timely manner and in the most meaningful form increases the operator s awareness of the current conditions in the process. Process operators are expected to exercise due diligence in the supervision of the process, and timely recognition of an abnormal situation reduces the likelihood that the situation will progress to the hazardous state. Figure 8-88 depicts the layers of safety protection in a typical chemical jdant. 

This is a location safer than Zone I with a likelihood of concentration of explosive gases, chemical vapour or volatile liquids during processing, storage or handling. This would become a fire hazard only under abnormal conditions, such as a leakage or a burst of joints or pipelines etc. Such a condition may exist only for a short period. A standard motor with additional features, as di.scussed below, may also be safe for such locations. A non-sparking type. Ex. n , or an increased safety motor, type Ex. e , may also be chosen for such locations. 

The frequency analysis step involves estimating the likelihood of occurrence of each of the undesired situations defined in the hazard identification step. Sometimes you can do this through direct comparison with experience or extrapolation from historical accident data. While this method may be of great assistance in determining accident frequencies, most accidents analyzed by QRA are so rare that the frequencies must be synthesized using frequency estimation methods and models. 

The risk to a person in the vicinity of a hazard. This includes the nature of the injury to the individual, the likelihood of the injury occurring, and the time period over which the injury might occur... 

MSDS Material Safety Data Sheet - a document that provides pertinent information and a profile of a particular hazardous substance or mixture. An MSDS is normally developed by the manufacturer or formulator of the hazardous substance or mixture. The MSDS is required to be made available to employees and operators whenever there is the likelihood of the hazardous substance or mixture being introduced into the workplace. Some manufacturers prepare MSDS for products that are not considered to be hazardous to show that the product or substance is not hazardous. 

Hazard analysis (HAZAN) is a quantitative way of assessing the likelihood of failure. Other names associated with this technique are risk analysis, quantitative risk assessment (QRA), and probability risk assessment (PRA). Keltz [44] expressed the view that HAZAN is a selective technique while HAZOP can be readily applied to new design and major modification. Some limitations of HAZOP are its inability to detect every weakness in design such as in plant layout, or miss hazards due to leaks on lines that pass through or close to a unit but cany material that is not used on that unit. In any case, hazards should... 

Exposure or the likelihood of exposure is the key. If the likelihood of exposure of any worker (ineluding elerieal workers) exists, an assessment should be eondueted. The site eontrols that have been designed and installed to limit aeeess or exposure must be monitored. These eontrols should be installed so that there are multiple levels (dependent on the severity of the hazard). If one level fails, the next level should be suflfi-eient to proteet workers until repairs to the first level ean be eompleted. 

For most hazardous waste sites with proper planning the situation is known before remediation activities begin. The support zone location needs to be carefully considered at the planning stages of the project. A better solution to the theoretical problem at hand would be to move the support zone further from the source of contamination. If the support zone can be placed far enough away, the likelihood for exposure at the support zone is minimized. 

What is the likelihood of missing an industry specific hazard when using a general scheme ... 

Another danger of an inadequate appreciation of human causes of hazards is that the HAZOP analyst may consider a particular high risk event (identified by a guide word and deviation) to be noncredible, because he or she only takes into accoimt the hardware failures (with an extremely low probability) that could give rise to the event. When human causes are taken into accoimt, the likelihood of the event may actually be quite high. 

Assume that the system described below exists in a process unit recently purchased by your company. As the manager, the safety of this unit is now your responsibility. You are concerned because your process hazard analysis team identified the potential for an operator error to result in a rupture of the propane condenser. You have commissioned a human reliability analysis (HRA) to estimate the likelihood of the condenser rupturing as the result of such an error and to identify ways to reduce the expected frequency of such ruptures... 

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. 

The Chemical Process Industry (CPI) uses various quantitative and qualitative techniques to assess the reliability and risk of process equipment, process systems, and chemical manufacturing operations. These techniques identify the interactions of equipment, systems, and persons that have potentially undesirable consequences. In the case of reliability analyses, the undesirable consequences (e.g., plant shutdown, excessive downtime, or production of off-specification product) are those incidents which reduce system profitability through loss of production and increased maintenance costs. In the case of risk analyses, the primary concerns are human injuries, environmental impacts, and system damage caused by occurrence of fires, explosions, toxic material releases, and related hazards. Quantification of risk in terms of the severity of the consequences and the likelihood of occurrence provides the manager of the system with an important decisionmaking tool. By using the results of a quantitative risk analysis, we are better able to answer such questions as, Which of several candidate systems poses the least risk Are risk reduction modifications necessary and What modifications would be most effective in reducing risk ... 

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