Hazard analysis direct causes

FTA is a backward logic, deduction-type hazard analysis method. In the case of ETA (see Clause 2.0), forward, inductive-based logic has been discussed. Both inductive and deductive types have been illustrated in Fig. V/3.0-1B, with explanations of why they are called forward or backward logic. In hazard analysis, a cause creates accidental events, which results in consequences. They can be looked at from different perspectives also. An inductive method is from specific (event) to general (consequences). On the contrary, in a deductive method, it is from general (event/ consequence) to specific (set of causes). In the case of an inductive method, analysis is carried out from event to consequence in forward direction. In a deductive method, analysis is carried out to find the causes from event in the reverse order. 

According to the modem accident-causation (G. and B. et al., 2005), from the point of individual behavior-safety control, hazard is embodied unsafe act (behavior) and unsafe condition meanwhile, under certain situation, unsafe act (behavior) can transform and result in unsafe condition. The unsafe act and unsafe condition is the direct cause of accident, deeper analysis comes to the indirect (common) cause, which include three elements inadequate safety knowledge, inadequate safety awareness, and inadequate safety habit. 

Software hazard analysis (SWHA) is a system safety analytical technique whose primary function is to systematically evaluate any potential faults in operating system and applications software requirements, codes, and programs as they may affect overall system operation. The purpose of the SWHA is to ensure that safety specifications and related operational requirements are accurately and consistently translated into computer software programs. In this regard, the analysis will verify that specific operational safety criteria, such as failsafe or fail-passive, have been properly assimilated into operational software. The SWHA will also identify and analyze those computer software programs, routines, or functions that may have direct control over or indirect influence on the safe operation of a given system. Also, in the operation of the computer software command function, there is a potential that the actual coded software may cause identified hazardous conditions to occur or inhibit a desired function, thereby creating additional hazard potential. 

Software Fault Hazard Analysis Similar in concept and structure to the system hazard analysis (SHA), which is conducted on system hardware, the software fault hazard analysis will analyze and evaluate a computer software program to identify critical areas in the programming that may contribute to or directly cause a hazard risk. Such risks may be due to an undetected hardware failure or incorrect inputs into the operation of the system software. The software FHA will also attempt to uncover any probable errors that can possible develop in the software after system activation. 

Accidents are usually complex and are the result of multiple causes. A detailed analysis of an accident will normally reveal three cause levels basic, indirect, and direct. At the lowest level, an accident results only when a person or object receives the release of an amount of energy or exposure to hazardous material that cannot be absorbed safely. This energy or hazardous material is the direct cause of the accident. The second causal areas are usually the result of one or more unsafe acts or unsafe conditions, or both. Unsafe acts and conditions are the indirect causes or symptoms. In turn, indirect causes are usually traceable to poor management policies and decisions, or to personal or environmental factors. These are the basic causes. 

This section will deal briefly with some aspects of expls safety peculiar to neutron activation analysis expts. We are concerned here with a) the possible effect of the ionizing radiation dose on the energetic material which will cause it to be more sensitive or hazardous to normal handling as an expl, and b) the potential direct expl hazards involved in the physical and mechanical transportation of samples to and horn the irradiation source and in a nuclear counting system... 

The risk analysis and evaluation will form the heart of the safety case. It is here where the argument and evidence is set out to justify the report s safety claims. This information is inextricably linked to the detail in the hazard register but in the safety case one has the opportunity for further explanation and elaboration. The hazard register typically has a formal structure to support cohesion and consistency between hazards. The fiee-form text of the safety case facilitates articulation and openness enabling us to support our argument with direct and indirect evidence. Essentially the text provides the necessary inference between the hazards, causes, controls and evidence that is needed to justify the argument. 

If control system equipment failure can cause an initiating event, then quantitative analysis must be done for all components where failure might initiate a hazard. For those failures with no other protection layer, the frequency of failure will result directly in an incident. The detailed quantitative analysis must show that these failures will not increase risk beyond tolerable levels. 

Measures of toxicity are from two routes. Firstly, data from laboratory testing on animals by direct injection, oral or chemical administration and is usually expressed as an LD50 value. This is the dose that causes death to 50% of the population after 14 days expressed as mg or fig of substance per kg body weight. Tests are performed under standard conditions and subject to rigorous statistical analysis. The lethal concentration (LC50) unit is used for hazardous airborne concentrations and is defined as the 4-hour inhalation of which causes death of 50% of the test group within the 14 day observation period. 

The definition of hazard earlier in this chapter lists three elements that can lead to accidents activities, conditions and circumstances. Causes of accidents often involve unsafe acts (activities) and unsafe conditions. When performing risk analysis, one may also consider circumstances surrounding a potential event. It is not uncommon for the circumstances to add to the severity of the event. For example, an automobile crashing into another vehicle may deflect into a gasoline storage tank located nearby but not directly involved in an incident. The event just happens to occur at the tank s location. 

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