Tolerance fatality rates

Since there are 10 sources of risk (at the same place) the maximum tolerable fatality rate (per risk) is lO /lO = 10 pa. 

How situational is occupational risk acceptance What variations does society tolerate in risky occupational exposures The Bureau of Labor Statistics (BLS) report titled National Census of Fatal Occupational Injuries in 2005 states that the rate at which fatal work injuries occurred in 2005 was 4.0 per 100,000 workers. The data in Table 1 gives the fatality rates for the five occupations having the highest fatality rates in 2005. 

Similarly, in continuous mode for the case of a boiler, if on account of loss of flame there is accumulation of CO and there could be an explosion, 1 in 500 cases leads to a fatality. If the boiler tolerable failure rate is 10 pa, and if failure rate because of loss of flame is A, then 10 > A 1/500. So A = 500 10 = 5 x 10 that is, S1L2. 

Although the fatality rates among all employment categories are the highest for the occupations shown in Table 6.1, the public has not demanded discontinuation of the operations in which they occur. Inherent risks in the high-hazard categories are considered tolerable in relation to the benefit attained. However, it should be recognized that there has been considerable research to make those occupations safer. ... 

SET MAXIMUM TOLERABLE FAILURE RATES by carrying out a quantified risk assessment based on a maximum tolerable probability of death or injury, arising from the event in question. This is dealt with in the next Chapter and takes into account how many simultaneous risks to which one is exposed in the same place, the number of fatalities and so on. 

As a simple example of selecting an appropriate SIL, assume that the maximum tolerable frequency for an involuntary risk scenario (e.g., customer killed by explosion) is 10 pa (A) (see Table 2.1). Assume that 10 (B) of the hazardous events in question lead to fatality. Thus the maximum tolerable failure rate for the hazardous event will be C = A/B = 10 pa. Assume that a fault tree analysis predicts that the unprotected process is only likely to achieve a failure rate of 2 x 10 pa (D) (i.e., 1/5 years). The FAILURE ON DEMAND of the safety system would need to be E = C/D =10 column of Table 1.1, SIL 2 is applicable. 

SR/15 describes both quantitative and risk matrix approaches to establishing target SILs but a very strong preference for the quantitative approach is stressed. It addresses the setting of maximum tolerable risk targets (fatality rates). The tolerable risk targets were shown in Chapter 2 of this book. 

Maximum Tolerable Failure Rate Involving Alternative Propagations to Fatality... 

The probability of an incident becoming fatal has been estimated, elsewhere, as 8.1%. The maximum tolerable risk has been set as 10 pa, thus the maximum tolerable incident rate is 10 /8.1% = 1.2 X 10 pa (Gate Gl). 

Maximum tolerable failure rate leading to single fatality is 10 pa/10 = 10 pa ... 

Risk tolerance can heavily depend on the social norms of a particular society at a particular era. For example Extremely high fatality rates of coal mine labors were an acceptable norm in Europe about a century ago. 

Clinically, GM-CSF or G-CSF have been used to accelerate recovery after chemotherapy and total body or extended field irradiation, situations that cause neutropenia and decreased platelets, and possibly lead to fatal septic infection or diffuse hemorrhage, respectively. G-CSF and GM-CSF reproducibly decrease the period of granulocytopenia, the number of infectious episodes, and the length of hospitalization in such patients (152), although it is not clear that dose escalation of the cytotoxic agent and increased cure rate can be rehably achieved. One aspect of the effects of G-CSF and GM-CSF is that these agents can activate mature cells to function more efficiently. This may, however, also lead to the production of cytokines, such as TNF- a, that have some toxic side effects. In general, both cytokines are reasonably well tolerated. The side effect profile of G-CSF is more favorable than that of GM-CSF. Medullary bone pain is the only common toxicity. 

Diet should be modified only in cases where foods have been proven to elicit symptoms. Patients with mastocytosis and Hymenoptera venom exposure are at risk for severe anaphylaxis. Thus, specific immunotherapy should be considered in patients with Hymenoptera venom allergy and then administered under close supervision [31]. The majority of patients with mastocytosis reportedly tolerate immunotherapy without significant side effects and appear protected following this approach [33,40]. However, there does appear to be some increased risk for adverse reactions during initiation of immunotherapy, as well as for therapy failures [31, 33]. An increased maintenance dose of insect venom has been reported to carry better success rates by sting provocation [41]. Also, in the light of 2 fatal cases of anaphylaxis after discontinuation of SIT in patients with mastocytosis [30], lifelong immunotherapy should be considered [26]. 

Opioids depress respiration via the ji2-receptor at the level of the medulla and thereby increase PCO2. Opioids reduce respiration, an effect that is fatal in the case of overdose, by a dual action. The opioids decrease both the sensitivity of the medulla to carbon dioxide concentrations and the respiratory rate. Cardiovascular function and the response to hypoxia are not compromised. By contrast, tolerance to the respiratory depressant effects of the opioids does not appear to occur, while tolerance to the emetic effects of the opioids occurs upon repeated administration. The area postrema chemoreceptor trigger zone of the medulla mediates opioid-induced vomiting. 

Failure rate Xj(t) for failures of category 1 with the most serious impact on persons, assets and environment must be lower than 10 to one shot (see Fig. 3). This value of failure rate ensures that failures with fatal (deadly) consequences are practically impossible. The given value of safety risk actually tolerates weapon failure resulting in death (category 1 failure) not more than one in 1 milliard of shots. 

Based on the failure rate, the risk tolerable frequency can be estimated. Such things are possible in simpler cases, as given in the example later. Referring to the storage tank example as shown in Fig. VII/1.4 1 (or Fig. Vlll/1.2.2-1), let this hydrocarbon storage area be manned 2 h per shift, that is, 6 h a day. On account of overpressure there may be leak that could cause an explosion and (say) out of 15 such leaks there will be one explosion causing a fatality. Analysis indicates that every 6 years there is an explosion. Let the tolerable frequency of explosion be 10. The required PFD can be found by direct calculation ... 

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