TYPICAL INITIATING EVENTS

The Top Event of a safety tree is usually of the form Person Seriously Injured or Killed, or Worker Suffers Lost Time Injury. The Initiating Event, whose dimension is inverse time, starts the accident sequence that could lead to the occurrence of the Top Event. Typical initiating events are ... 

Customisable data to easily configure SIL Comp to your company standards, in particular Risk Profile, Risk Matrix, typical Initiating Events and Failure Rates... 

Layer of protection analysis (LOPA) is a simplified form of event tree analysis. Instead of analyzing all accident scenarios, LOPA selects a few specific scenarios as representative, or boundary, cases. LOPA uses order-of-magnitLide estimates, rather than specific data, for the frequency of initiating events and for the probability the various layers of protection will fail on demand. In many cases, the simplified results of a LOPA provide sufficient input for deciding whether additional protection is necessary to reduce the likelihood of a given accident type. LOPAs typically require only a small fraction of the effort required for detailed event tree or fault tree analysis. 

Frequency Phase 1 Perform Qualitative Study, Typically Using HAZOP, FMEA, or What-if Analysis. To perform a qualitative study you should first (1) define the consequences of interest, (2) identify the initiating events and accident scenarios that could lead to the consequences of interest, and (3) identify the equipment failure modes and human errors that could contribute to the accident... 

A transient, is a passing event which may upset the reactor operation but does not physically damage the primary cooling envelope. Table 6.1-1 lists PWR transient initiating events that ha c been used in PRA preparation. Typical frontline systems that mitigate LOCAs and transients for a PWR are presented in Table 6.1-2. The frontline systems must be supported by support systems interactions between both are presented in Table 6.1 -3 for ANO-1 (Arkansas Nuclear Unit 1). 

In the previous chapter, a comprehensive description was provided, from four complementary perspectives, of the process of how human errors arise during the tasks typically carried out in the chemical process industry (CPI). In other words, the primary concern was with the process of error causation. In this chapter the emphasis will be on the why of error causation. In terms of the system-induced error model presented in Chapter 1, errors can be seen as arising from the conjunction of an error inducing environment, the intrinsic error tendencies of the human and some initiating event which triggers the error sequence from this imstable situation (see Figure 1.5, Chapter 1). This error sequence may then go on to lead to an accident if no barrier or recovery process intervenes. Chapter 2 describes in detail the characteristics of the basic human error tendencies. Chapter 3 describes factors which combine with these tendencies to create the error-likely situation. These factors are called performance-influencing factors or PIFs. 

The Millstone Unit 1 PRA contains component failure and maintenance unavailability data, and initiating event frequency data, including typical BWR anticipated operational occurrences and LOSP. 

The field of translation initiation has focused on the initial round ofribosomal subunit recruitment to an mRNA. Presumably, these events are mirrored in the subsequent rounds of initiation necessary for polyribosome formation. Importantly, because mRNAs are typically present in large polyribosomes (averaging 9-13 ribosomes per mRNA), the initiation events that govern ribosome recruitment to preexisting polyribosomes constitute the majority of translation initiation cycles occurring in an mRNA s lifetime. Whether or not these initiation events mimic the first round of initiation is not yet known. Since eukaryotic cells divide ribosomes between two subcellular compartments, the cytosol and ER membrane, it is also important to know if the mechanism of translation initiation on ER-bound ribosomes is similar to that occurring on soluble ribosomes and, importantly, whether ER-bound ribosomes can direcdy (re) initiate translation on bound polyribosmes. 

Like alkynes, a variety of mechanistic motifs are available for the transition metal-mediated etherification of alkenes. These reactions are typically initiated by the attack of an oxygen nucleophile onto an 72-metalloalkene that leads to the formation of a metal species. As described in the preceding section, the G-O bond formation event can be accompanied by a wide range of termination processes, such as fl-H elimination, carbonylation, insertion into another 7r-bond, protonolysis, or reductive elimination, thus giving rise to various ether linkages. 

The activation logic for and ESD system should be kept as simple at possible. Typically most facilities specify plateaus or levels of ESD activation. These levels activate emergency measures for increasing amounts or areas of the facility as the emergency involves a larger and larger area or the degree of hazard from the initial event. Low hazards or small area involvement would only require a shutdown of individual equipment while major incidents would require a facility shutdown. The shutdown of one of a facility should not present a hazard to another portion of the facility otherwise both should be shut down. Typical levels utilized in the petroleum and related industries are identified in Table 12. 

It is important to look beyond the initiating event to determine the potential for fire to spread to adjacent areas. If the fire is not detected early and quickly controlled, then the fire can escalate and involve other equipment and units. For escalation to occur, the fire must impact adjacent equipment by either radiant heat or flame impingement. In most risk assessments, escalation is taken into account by establishing a rule set. If any of the conditions within the rule set are exceeded, then escalation is assumed to occur. Typically, rule-sets may include ... 

Polymerization of monomer by vinyl addition polymerization is a typical chain process. Three main reaction stages can be identified initiation, propagation and termination. During the initiation event, free radicals are created. In a photopolymerization, the initiating free radicals are formed in a photoprocess. Propagation is the process of addition of monomer to the growing free radical chain. The destruction of the free radical center occurs during termination. 

Rapid termination of signalling by GPCRs is typically initiated by receptor phosphorylation events which are catalysed by second messenger activated-kinases or by GRKs (Lohse 1993). 

In this case, the termination steps are much less important than in the last case we looked at, and typically the chain reaction can continue for 106 steps for each initiation event (photolysis of chlorine). Be warned reactions like this can be explosive in sunlight. 

A scenario referred to as a sub-Chandrasekhar-mass supernova envisions a C-O WD capped with a helium layer accreted by a companion, and which explodes as the result of a hydrodynamical burning before having reached the Chandrasekhar limit. This type of explosions may exhibit properties which do not match easily the observed properties of typical SNIa events. It cannot be excluded, however, that they are responsible for some special types of events, depending in particular on the He accretion rate and on the CO-sub-Chandrasekhar WD (SCWD) initial mass (e.g. [85]). Unidimensional simulations of He cataclysmics characterized by suitably selected values of these quantities reach the conclusion that the accreted He-rich layer can detonate. Most commonly, this explosion is predicted to be accompanied with the C-detonation of the CO-SC WD. In some specific cases, however, this explosive burning might not develop, so that a remnant would be left following the He detonation. Multidimensional calculations cast doubt on the nature, and even occurrence, of the C-detonation in CO-SC WD (e.g. [86]). 

Reaction centers in photosynthetic bacteria typically contain three membrane-bound subunits (L, M, and H), and the following cofactors four bacteriochlo-rophyll (Bchl or B), two bacteriopheophytin (Bphe or 4>), two quinones (Q), and one Fe atom 28, 178). The sequence of electron transfer steps along the various cofactors has been established largely by spectroscopic methods. The primary donor, D, which initially absorbs light (creating the excited state D ) is a dimer of Bchl molecules [also designated (Bchl)2 or P]. Electron transfer proceeds from D to an intermediate acceptor (a Bphe molecule), to a primary acceptor, Qa, and finally to the secondary acceptor Qb. After these initial events, the RC... 

Non-accident-initiated events differ in that the event is not associated with an external impact during transport. Typical non-accident-initiated events that may be reviewed as part of a transportation risk analysis may not be mode-specific, and could include ... 

The chance of an incident is generally a function of the distance traveled. Thus, the frequency of an accident is often expressed as an accident rate per mile. Contributions from non-accident-initiated events are typically expressed on a frequency-per-hour or per-year basis. Thus, the duration of the hazardous materials movement is a key parameter. Figure 5.3 illustrates the basic calculation sequence for one trip or movement. If multiple trips are made, the total risk is equal to the number of trips times the risk per trip. The basic calculation sequence will have minor variations for each mode of transport and can be broken down into greater detail as needed. Increased detail might include different accident rates and lengths for each segment of a route or might explicitly address the accident rates and release probabilities for different accident causes. Inputs to the analysis that may be altered or may influence the calculation include ... 

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