Hazards basic causes

The PHA team constructs a tree that has as its starting point an unwanted hazardous event. Causes of this top event are identified, together with precursor causes, to develop the tree downward to basic causes, for which occurrence frequencies are available. Calculation procedures yield a top event frequency that, if not tolerable, can be reduced by adding safety systems to minimize the effects of component or human failures. 

CONSTRUCTING THE FAULT TREE. Fault tree construction begins at the top event and proceeds, level by level, until all fault events have been traced to their basic contributing events or basic events. The analysis starts with a review of system requirements, function, design, environment, and other factors to determine the conditions, events, and failures that could contribute to an occurrence of the undesired top event. The top event is then defined in terms of sub-top events, i.e., events that describe the specific "whens and wheres" of the hazard in the top event. Next, the analysts examine the sub-top events and determine the immediate, necessary, and sufficient causes that result in each of these events. Normally, these are not basic causes, but are intermediate faults that require further development. For each intermediate fault, the causes are determined and shown on the fault tree with the appropriate logic gate. The analysts follow this process until all intermediate faults have... 

In regard to accident ratios, property damage accidents occur more often than any other type of accident. Property damage accidents are therefore opportunities to identify the basic causes and take steps to eliminate similar accidents. It will be appreciated that should a similar accident occur, because of hazards that have not been rectified, the outcome may be different. The next time the accident may result in injury, damage, business interruption, or a combination of these. 

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. 

While we often think of hazardous acts and conditions as the basic causes of accidents, actually they are symptoms of failure on another level. Unsafe acts and unsafe conditions can usually be traced to three basic causes poor management policies and decisions, personal factors, and the physical facility design. 

A detailed description of the direct, indirect, and basic causes of accidents can be found in Chapter 7. Remember, the unplanned or unwanted release of excessive amounts of energy or hazardous materials causes most accidents. With few... 

FTA is somewhat similar to fish-bone analysis another hazard analysis method (Fig. V/3.0-4). When compared with fishbone analysis shown and discussed in Fig. V/3.0-3 and Fig. V/3.0-4 respectively, FTA is more formal and specific, that is, it resolves basic causes for the accidental event or consequences. 

It involves a bottom-up assessment of each hazard and is focused on the post hazard horizon The sequence of intermediate conditions identified is termed the hazard development scenario . Defences against potential escalation (the defence may be equipment, procedure or circumstance) are referred to as Barriers . The Consequences of a hazard are categorised into three broad categories, Safety, Cotmnercial and Enviromnental. An example of basic Cause- Consequence risk model structure is given in Figure 3-12. 

DRM Method In step 3, a complete list of hazards is identified that are associated with the operation/ system to be assessed. The list should include a large number and diversity of possible hazards. In addition to the Operational Hazards (identified at the level of the ATM service provided to Airspace Users) this includes hazards and conditions that may lead to a safety relevant situation (basic causes, root hazards), hazards and conditions that may hamper the resolution of the safety relevant situation (resolution hazards), and preexisting hazards (those aviation hazards that are not caused by the ATM system but that are aimed to be prevented or mitigated by the ATM system). All the hazards identified here will be referred to in the following as hazards . 

You should look at each of these basic accident types to identify procedures, processes, occupations and tasks that present a hazard to cause one of the accident types in the following section. 

If management and the workforce do not tolerate the existence of hazards and constantly ask the qnestion, How could this have happened they are better able to get to the basic causes of adverse workplace events. 

First, we can prevent them by knowing what caused the accidents to happen in the first place. Accident investigators perform that task. The accident investigator determines the direct, indirect, and basic causes of an accident. But prevention doesn t stop there. The next step is putting the knowledge to work. If hazards can be recognized and identified, then the workforce ean help prevent accidents. 

A detailed description of the direct, indirect, and basic causes of accidents can be found in Chapter 7. Remember, the unplanned or unwanted release of exeessive amounts of energy and hazardous materials cause most accidents. With few exceptions, these releases are caused by unsafe acts and unsafe conditions. An unsafe act or an unsafe condition may trigger the release of large amounts of energy or hazardous materials. This may cause the accident. (See Figure 14-3.) Particular attention should be paid to these areas. 

Use the hazard study 2 guidelines in Chapter 3 to identify potential risks. The study team should apply the guide diagram 1 to identify possible hazards and basic causes. Use guide diagram 2 to identify possible consequences. 

Fault Tree Analysis Faiilt tree analysis permits the hazardous incident (called the top event) frequency to be estimated from a logic model of the failure mechanisms of a system. The top event is traced downward to more basic failures using logic gates to determine its causes and hkelihood. The model is based on the combinations of fail-... 

Loss-of-Containment Causes The list in Table 23-30 indicates four basic ways in which containment can be lost. These cause cate-ories can be used both as a checklist of considerations during the esign process and as a starting point for evaluating the adequacy of safeguards as part of a process hazard and risk analysis. 

CERCLA, or Superfund, was enacted in 1980, and amended in 1986, for the basic purpose of providing funding and enforcement authority to clean up any site where there is a past unremedied release of a hazardous substance or hazardous substance spill. Such sites are typically characterized as areas where hazardous waste or materials have been disposed of improperly, with litde if any responsible action being taken to mitigate the situation. Standards for financial responsibility were promulgated by the SARA of 1986 which further amended Section 9003 of RCRA and mandated that the EPA establish financial responsibility requirements for UST owners and operators to guarantee cost recovery for corrective action and third-party liability caused by accidental releases of USTs containing petroleum products. 

Because of the hazards caused by such explosive boiling incidents, industry has supported research programs seeking answers to several basic questions ... 

In addition to the importance of combustion reactors in chemical processes, mcon-troUed combustion reactions create the greatest potential safety hazard in the chemical industry. Therefore, all chemical engineers need to understand the basic principles of combustion reactors to recognize the need for their proper management and to see how improper management of combustion can cause unacceptable disasters. 

In the UK chemicals strategy the statement The Government is very concerned that we do not have adequate information about the hazards of most chemicals released into the environment in large quantities is emphasized in bold in section 1.7 (DETR, 1999). The EU strategy states that The lack of knowledge about the impact of many chemicals on human health and the environment is a cause for concern (CEC, 2001, p4). The Royal Commission on Environmental Pollution held an inquiry into chemicals that reported in 2003. They consider that our failure to understand the interactions between synthetic chemicals and the natural environment, and most of all our failure to compile even the most basic information about the behaviour of chemicals in the environment, is a serious matter (RCEP, 2003, pi). 

Bases are characterized by their bitter taste and slippery feel. Interestingly, bases themselves are not slippery. Rather, they cause skin oils to transform into slippery solutions of soap. Most commercial preparations for unclogging drains are composed of sodium hydroxide, NaOH (also known as lye), which is extremely basic and hazardous when concentrated. Bases are also heavily used in industry. Each year in the United States about 25 billion pounds of sodium hydroxide is manufactured for use in the production of various chemicals and in the pulp and paper industry. Solutions containing bases are often called alkaline, a term derived from the Arabic word for ashes (al-qali), a term we met in Section... 

Stochastic Responses. A basic principle of health protection for both radionuclides and hazardous chemicals is that the probability of a stochastic response, primarily cancers, should be limited to acceptable levels. For any substance that causes stochastic responses, a linear dose-response relationship, without threshold, generally is assumed for purposes of health protection. However, the probability coefficients for radionuclides and chemicals that induce stochastic responses that are generally assumed for purposes of health protection differ in two potentially important ways. 

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