Minimal Risk Levels Research Articles

Bank Capital Standards for Market Risk: A Welfare Analysis

We propose a simple model that is suitable for evaluating alternative bank capital regulatory proposals for market risk. Our model formalizes the conflict between bank objectives and regulatory goals. Banks' decisions represent a tension between their desire to exploit the deposit-insurance put option and their desire to preserve franchise value. Regulators seek to balance the social value of deposits in mediating transactions against the deadweight costs of failure resolution. Our social welfare criterion is standard: a weighted average agents' utilities. We demonstrate that banks do not incrementally alter their portfolio risk as the economic environment changes. Rather, banks either choose the minimal feasible risk or the maximal feasible risk. This pattern, in turn, drives regulatory decisions: The first goal of the regulator is to induce banks to choose the minimal risk level. For all nontrivial cases, unregulated banks fail to choose the first-best allocations. Traditional ex-ante capital requirements can induce banks to choose the socially-optimal level of portfolio risk, but the required capital is often inefficiently high. In contrast, variants of the Federal Reserve Board's precommitment proposal imply far smaller efficiency losses, and achieve allocations at or near the first-best for most reasonable model specifications. The ex-post penalties required for the optimal implementation of precommitment are not excessively large. The welfare gains from precommitment are even higher when the precommitment penalty function is precluded from sending banks into default. We conclude that state-contingent regulatory mechanisms, of which the precommitment approach is an example, offer the possibility of substantial gains in regulatory efficiency, relative to traditional state non-contingent regulation.

Bank Capital Standards for Market Risk: A Welfare Analysis *

We propose a simple model that is suitable for evaluating alternative bank capital regulatory proposals for market risk. Our model formalizes the conflict between bank objectives and regulatory goals. Banks' decisions represent a tension between their desire to exploit the deposit-insurance put option and their desire to preserve franchise value. Regulators seek to balance the social value of deposits in mediating transactions against the deadweight costs of failure resolution. Our social welfare criterion is standard: a weighted average agents' utilities. We demonstrate that banks do not incrementally alter their portfolio risk as the economic environment changes. Rather, banks either choose the minimal feasible risk or the maximal feasible risk. This pattern, in turn, drives regulatory decisions: The first goal of the regulator is to induce banks to choose the minimal risk level. For all nontrivial cases, unregulated banks fail to choose the first-best allocations. Traditional ex-ante capital requirements can induce banks to choose the socially-optimal level of portfolio risk, but the required capital is often inefficiently high. In contrast, variants of the Federal Reserve Board's precommitment proposal imply far smaller efficiency losses, and achieve allocations at or nearthe first-best for most reasonable model specifications. The ex-post penalties required for the optimal implementation of precommitment are not excessively large. The welfare gains from precommitment are even higher when the precommitment penalty function is precluded from sending banks into default. We conclude that state-contingent regulatory mechanisms, of which the precommitment approach is an example, offer the possibility of substantial gains in regulatory efficiency, relative to traditional state non-contingent regulation.

Optimal multi-currency investment strategies with exact attribution in three Asian countries

The exact and complete return attribution framework of Singer and Karnosky (1995) does not account for risk, since it ignores accumulated historical information. Its implied investment strategy selection is based on simple return maximization and ignores that investment strategies are correlated via intra- and intermarket risks. Using simple tensor algebra we extend their exact accounting framework to include market risk measurements for n countries. The resulting n 2× n 2 strategy risk matrix exactly decomposes into a tensor sum of the n× n fundamental market risk matrices. Since the strategy risk matrix is singular with rank=2 n−1< n 2, the resulting portfolio choice problem is degenerate. But, the portfolio constraints imposed by the exact accounting framework allows one to solve the conventional Markowitz' mean-variance optimization problem as a nondegenerate lower dimensional problem of fundamental investment choice between stock markets and currency overlays, with a nonsingular 2 n×2 n risk matrix. The original n 2 investment strategy allocations are then uniquely retrieved from the resulting 2 n optimal investment choices. Thus, we solve also the problem of the optimization of complete, exact investment strategy portfolios, like RiskMetrics ™ and CreditMetrics ™. Our complete and exact return-risk attribution accounting framework is applied to monthly return data of Singapore, Malaysia and Indonesia from July 1992 through June 1997. The average historically maximal simple and risk-adjusted investment strategy returns are compared with the efficiency frontier computed for the 5 year horizon of an `efficiency-seeking' global investor to determine their implied minimal risk levels. Furthermore, the paper analyzes which markets exhibit most risk in these Asian countries. The evidence shows that most of the risk is attributable to the magnitudes of the risks of the stock markets, followed by those of the currency markets and the cash markets.

The use of hematological effects in the development of minimal risk levels.

The Agency for Toxic Substances and Disease Registry (ATSDR) derives minimal risk levels (MRLs) to assist in evaluating risk of adverse health effects in individuals exposed to hazardous substances. MRLs are derived from published values identifying no-observed-adverse-effect levels (NOAELs) or lowest-observed-adverse-effect levels (LOAELs) in animal or human studies. The most sensitive end points are used. To date, 4 inhalation MRLs and 13 oral MRLs have been derived from hematological end points for 12 substances. This paper provides a brief overview of the hematological system, examples of hematological end points, and the MRL for substances with hematological end points.

Health effects classification and its role in the derivation of minimal risk levels: developmental effects.

Agency for Toxic Substances and Disease Registry (ATSDR) utilizes chemical-specific minimal risk levels (MRLs) to assist in evaluating the public health risk associated with exposure to hazardous substances. The MRLs are derived based on the health effects data compiled from current literature searches and presented in ATSDR's toxicological profiles. Health effects are categorized according to their degree of severity (e.g., serious, less serious, minimal, and not adverse). This evaluation is important, because each respective category can be assigned a different amount of uncertainty, thus affecting the final value of the calculated MRL. From the total of 272 MRLs derived as of December 1997, 21 were based on developmental effects. ATSDR's ranking of developmental health effects as described in the Guidance for Developing Toxicological Profiles and specific examples of how the categorized health effects were used in MRL derivations are provided in this paper.

Tests and optimal guarded weights of evidence

Optimal guarded weights of evidence for simple alternatives to a hypothesis are shown to belong to two distinct classes, depending on whether or not they include test critical functions as limiting cases for distant alternatives. In particular, it is shown that for shift families with monotone likelihood ratio, as the alternative moves infinitely far from the hypothesis, the minimum risk level- α weight of evidence for the alternative approaches a level- α Neyman–Pearson test critical function if and only if the score function is unbounded. The results are extended to a class of one-parameter families with monotone likelihood ratio, in particular exponential families. Examples include scale and shape parameters.

Health effects classification and its role in the derivation of minimal risk levels: neurological effects.

The agency for Toxic Substances and Disease Registry (ATSDR) uses substance-specific minimal risk levels (MRLs) to assist in evaluating public health risks associated with exposure to hazardous substances. By definition, "MRLs are estimates of daily human exposure to a chemical that are likely to be without an appreciable risk of adverse noncancer health effects over a specified duration of exposure." MRLs serve as screening levels for health assessors to identify contaminants and potential health effects that may be of concern for population living near hazardous waste sites and chemical releases. MRLs for each substance are derived for acute (1-14 days), intermediate (15-364 days), and chronic (365 days and longer) exposure durations, and for the oral and inhalation routes of exposure. The MRLs are derived from data compiled from a current comprehensive literature search and are presented in ATSDR's toxicological profile for that substance. In this paper we outline ATSDR's guidance for evaluating the neurological end point as discussed in the agency's toxicological profiles. Ranking neurological effects into less serious and serious categories and applying this procedure to the derivation of health guidance values or MRLs are also described. Specific examples of ATSDR MRLs based on neurological effects are presented.

INVESTIGATION OF THE POTENTIAL IMPACT OF BENCHMARK DOSE AND PHARMACOKINETIC MODELING IN NONCANCER RISK ASSESSMENT

There has been relatively little attention given to incorporating knowledge of mode of action or of dosimetry of active toxic chemical to target tissue sites in the calculation of noncancer exposure guidelines. One exception is the focus in the revised reference con centration (RfC) process on delivered dose adjustments for inhaled materials. The studies reported here attempt to continue in the spirit of the new RfC guidelines by incorporating both mechanistic and delivered dose information using a physiologically based pharmaco kinetic (PBPK) model, along with quantitative dose-response information using the bench mark dose (BMD) method, into the noncancer risk assessment paradigm. Two examples of the use of PBPK and BMD techniques in noncancer risk assessment are described: methylene chloride, and trichloroethylene. Minimal risk levels (MRLs) based on PBPK analysis of these chemicals were generally similar to those based on the traditional process, but individual MRLs ranged from roughly 10-fold higher to more than 10-fold lower than existing MRLs that were not based on PBPK modeling. Only two MRLs were based on critical studies that presented adequate data for BMD modeling, and in these two cases the BMD models were unable to provide an acceptable fit to the overall dose-response of the data, even using pharmacokinetic dose metrics. A review of 10 additional chemicals indicated that data reporting in the toxicological literature is often inadequate to support BMD modeling. Three general observations regarding the use of PBPK and BMD modeling in noncancer risk assessment were noted. First, a full PBPK model may not be necessary to support a more accurate risk assessment; often only a simple pharmacokinetic description, or an understanding of basic pharmacokinetic principles, is needed. Second, pharmacokinetic and mode of action considerations are a crucial factor in conducting non cancer risk assessments that involve animal-to-human extrapolation. Third, to support the application of BMD modeling in noncancer risk assessment, reporting of toxicity results in the toxicological literature should include both means and standard deviations for each dose group in the case of quantitative endpoints, such as relative organ weights or testing scores, and should report the number of animals affected in the case of qualitative endpoints.

Public Health Guidance Values for Chemical Mixtures: Current Practice and Future Directions

Agency for Toxic Substances and Disease Registry (ATSDR) utilizes chemical-specific minimal risk levels (MRLs) to assist in evaluating public health risks associated with exposure to hazardous substances. The MRLs are derived based on the data compiled from current worldwide literature searches and presented in ATSDR's toxicological profiles. These documents profile not only individual chemicals, but also groups of chemically related compounds and chemical mixtures. ATSDR took several approaches when developing MRLs for chemical mixtures. In some instances, toxicity equivalency factors were used to estimate the toxicity of the whole mixture; in other instances, the most toxic chemical was assumed to drive the health assessment for the whole mixture. Another approach was to treat the mixture as one entity and develop a health guidance value for the whole mixture. In yet another approach, each chemical of the mixture was evaluated separately and several health guidance values were developed. In the future, ATSDR will evaluate priority chemical mixtures found at hazardous waste sites. A weight-of-evidence approach, physiologically based pharmacokinetic modeling and benchmark dose modeling, and quantitative structure–activity relationships will have an impact on the development of MRLs and the assessment of chemical mixtures.

A physiologically-based pharmacokinetic model assessment of methyl t-butyl ether in groundwater for a bathing and showering determination.

Methyl t-butyl ether (MTBE) is a gasoline additive that has appeared in private wells as a result of leaking underground storage tanks. Neurological symptoms (headache, dizziness) have been reported from household use of MTBE-affected water, consistent with animal studies showing acute CNS depression from MTBE exposure. The current research evaluates acute CNS effects during bathing/showering by application of physiologically-based pharmacokinetic (PBPK) techniques to compare internal doses in animal toxicity studies to human exposure scenarios. An additional reference point was the delivered dose associated with the acute Minimum Risk Level (MRL) for MTBE established by the Agency for Toxic Substances and Disease Registry. A PBPK model for MTBE and its principal metabolite, t-butyl alcohol (TBA) was developed and validated against published data in rats and humans. PBPK analysis of animal studies showed that acute CNS toxicity after MTBE exposure can be attributed principally to the parent compound since the metabolite (TBA) internal dose was below that needed for CNS effects. The PBPK model was combined with an exposure model for bathing and showering which integrates inhalation and dermal exposures. This modeling indicated that bathing or showering in water containing MTBE at 1 mg/L would produce brain concentrations approximately 1000-fold below the animal effects level and twofold below brain concentrations associated with the acute MRL. These findings indicate that MTBE water concentrations of 1 mg/L or below are unlikely to trigger acute CNS effects during bathing and showering. However, MTBE's strong odor may be a secondary but deciding factor regarding the suitability of such water for domestic uses.

Mercury from maternal "silver" tooth fillings in sheep and human breast milk. A source of neonatal exposure.

Neonatal uptake of mercury (Hg) from milk was examined in a pregnant sheep model, where radioactive mercury (Hg203)/silver tooth fillings (amalgam) were newly placed. A crossover experimental design was used in which lactating ewes nursed foster lambs. In a parallel study, the relationship between dental history and breast milk concentration of Hg was also examined in 33 lactating women. Results from the animal studies showed that, during pregnancy, a primary fetal site of amalgam Hg concentration is the liver, and, after delivery, the neonatal lamb kidney receives additional amalgam Hg from mother's milk. In lactating women with aged amalgam fillings, increased Hg excretion in breast milk and urine correlated with the number of fillings or Hg vapor concentration levels in mouth air. It was concluded that Hg originating from maternal amalgam tooth fillings transfers across the placenta to the fetus, across the mammary gland into milk ingested by the newborn, and ultimately into neonatal body tissues. Comparisons are made to the U. S. minimal risk level recently established for adult Hg exposure. These findings suggest that placement and removal of "silver" tooth fillings in pregnant and lactating humans will subject the fetus and neonate to unnecessary risk of Hg exposure.

Risk assessment of mixtures and standard setting: Working towards practical compromises

Basic concepts of ‘dose/concentration additivity’ and ‘response addition/independence’ may be applied to evaluate chemical mixtures in human toxicology, as well as in ecotoxicology. In the case of compounds that cause the same toxicological effect by the same mechanism, ‘dose addition’ is a more plausible form of joint action than ‘response addition’. Data on the effects of halogenated hydrocarbons on the kidney, the effects of organic solvents on the central nervous system, and the effects of organophosphates on cholinesterase, are the basis of this assumption. For such compounds, response addition will generally underestimate risk. None the less, both dose addition and response addition are ‘non-interactive’ forms of joint action. As such, neither additivity assumption will accurately predict risk for compounds that exhibit toxicological interactions regardless of the primary mechanism(s) of toxicity. More often, the additivity approach overestimates the risk of a combination of chemicals. From a public health perspective, such results over-protect the public; hence this approach can be used for standard setting. The introduction of a special safety factor of 10 for the standard setting for mixtures in addition to those normally used for deriving acceptable daily intakes, reference doses or minimal risk levels is not supported by data. Instead, each exposure scenario should be considered on a case-by-case basis. Furthermore, considerations of multiple endpoints, including multiple organs, multiple effects, multiple mechanisms and potential interactions between such mechanisms, are very desirable for overall toxicity and risk assessment of chemical mixtures. In conclusion, additivity could be used to estimate potential risks for a combination of chemicals: only if scientific data support independence of effects can response independence be used as an alternative for standard setting.

Breast-feeding exposure of infants to environmental contaminants--a public health risk assessment viewpoint: chlorinated dibenzodioxins and chlorinated dibenzofurans.

Exposure of children to chlorinated dibenzodioxins and chlorinated dibenzofurans via breast-feeding has been well-documented in industrialized countries. Recent studies indicate a possible link between development of subtle health effects in children and their exposure to dioxin-like chemicals from maternal milk. Some examples of the effects are lower vitamin K levels, increased thyroxine levels, and mild changes in liver enzymes. The projected daily intakes of chlorinated dibenzodioxins and chlorinated dibenzofurans are compared with minimal risk levels for intermediate duration oral exposure (15-365 days) derived for these chemicals. Public health recommendations for future actions related to infant intake of chlorinated dibenzodioxin- and chlorinated dibenzofuran-contaminated breast milk are also addressed.

Utilizing Uncertainty Factors in Minimal Risk Levels Derivation

The Agency for Toxic Substances and Disease Registry (ATSDR) utilizes chemical-specific minimal risk levels (MRLs) to assist in evaluating public health risks associated with exposure to hazardous substances. During MRL derivation, uncertainty factors (UF) are used. Under current ATSDR methodology, default UFs of 10 are applied to extrapolate from a lowest-observed-adverse-effect level (LOAEL) to a no-observed-adverse-effect level (NOAEL), for interspecies extrapolation and for intraspecies variability, However, chemical-specific toxicity information has sometimes made it necessary and appropriate to deviate from using the standard UF of 10. Since its inception in January 1993 until December 1994, ATSDR′s Interagency MRL Workgroup has derived 46 inhalation and 67 oral MRLs. When the substance-specific data permitted, the workgroup departed from the default UFs of 10 in 30 specific cases. Specific examples and rationales are presented in this paper.

Halogenated aromatic hydrocarbons and toxicity equivalency factors (TEFs) from the public health assessment perspective

The validity of the toxicity equivalency factors (TEFs) approach to predicting toxicity of mixtures was investigated on the basis of the public health risk assessment that had been posted for different groups of halogenated aromatic hydrocarbons. First, the minimal risk levels (MRLs) were derived based on the databases available for chlorinated dibenzo-p-dioxins (CDDs), chlorinated dibenzofurans (CDFs), and polychlorinated biphenyls (PCBs). The MRL values were then converted to 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TODD) toxicity equivalents (TEQs) and compared with each other. There was a good correlation between intermediate duration oral MRLs for TCDD and 2,3,4,7,8-pentaCDF when expressed in TEQs (7 pg/kg/day and 15 pg/kg/day). Although the studies that served for derivation of these MRLs used different species (guinea pigs and rats, respectively), the toxicity endpoints (immunological and hepatic for TCDD and hepatic for 2,3,4,7,8-pentaCDF) were comparable. The hepatic effects were measured by the same techniques (blood chemistry and histopathology), ensuring similar sensitivity. However, there was a discrepancy between acute oral MRLs for TCDD and 2,3,4,7,8-pentaMF when they were expressed in TEQs (20 pg/kg/day and 500 pg/kg/day, respectively). The studies used for MRL derivation involved not only different species (mice and guinea pigs, respectively), the immunotoxicity endpoints were measured by techniques with different sensitivity (serum complement activity versus histopathology), making comparison difficult. Further calculations showed that the TEFs approach may be feasible for individual coplanar congeners of PCBs, but not for a mixture of Aroclors. Correlations presented here support the concept that the TEFs are valid only if specific criteria for their derivation are met (e.g., a broad database of information, consistency across endpoints, additivity for the effects, a common mechanism of action, etc.). In environmental exposure, the total toxicity of halogenated aromatic hydrocarbons is not necessarily the sum of the total individual congener toxicities because individual congeners compete for the same receptor; therefore, nonadditive behavior may occur.

An integrated framework to identify significant human exposures (SHELs)

Typically, health risk assessment methodologies have been designed to assess risks associated with exposure to individual chemicals through one specific medium, such as air, water, or food. This is partly because classical experimental methodology is used to study pure chemicals, and partly because a majority of early promulgated environmental laws (e.g., Clean Air Act, Clean Water Act) regulated chemicals in a given matrix via a specific route. Often, however, exposures in the ambient environment are through multiple routes, multiple media and to multiple chemicals. Presented here is a multimedia framework that health risk assessors can use to identify significant human exposure levels (SHELs) on a site-specific basis. This framework is presented in the context of a decision tree that links health guidance values such as minimal risk levels (MRLs) with sites-pecific data, using a range of decision-support models. It includes a provision to estimate a level of concern by comparing the estimated total dose (exposures) with guidance values established by the Agency, by other federal organizations, and by basket-survey results. If a SHEL has been identified, a range of follow-up public health actions may be indicated (i.e., surveillance, health education, or other preventive interventions). This framework serves to (1) integrate the overall health assessment process, (2) evaluate the need for public health interventions, (3) incorporate innovative decision-support methods/models, and (4) demonstrate utility of such methods in public health practice and the pursuit of the Agency's mission.

Approach to Risk Assessment of PCDDs and PCDFs in Canada

The nongenotoxic classification for the ubiquitous environmental contaminants polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) implies that a toxicity threshold may exist. Therefore, a minimal risk level or tolerable daily intake (TDI) value can be estimated by identifying no observable adverse effect levels (NOAELs) from animal toxicological investigations and extrapolating this dose to humans by the use of safety factors. When available, data from epidemiological investigations are utilized and carry a larger "weighting" than the animal studies (i.e., smaller safety factors required). A complete database review for the most toxic congener of this class of halogenated aromatic hydrocarbons, 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD), yields a NOAEL of 1.0 ng/kg body wt/day for rat carcinogenicity (Kociba et al., Toxicol. Appl. Pharmacol. 46, 279-303, 1978) and reproductive toxicity (Murray et al., Toxicol. Appl. Pharmacol. 50, 241-252, 1979) effects. By employing a 100-fold safety factor to compensate for inter- and intraspecies variability, a tentative TDI value can be estimated at 10 pg/kg body wt/day. For food intake purposes, a total of 17 2,3,7,8-substituted PCDD/PCDF congeners are included in this estimate by using an additive toxic equivalency (TEQ) approach based on international toxic equivalency factors (I-TEFs) developed by NATO (NATO Report No. 178, 1988). This implies that averaged over an individual′s total lifespan (estimated at 70 years), 600 pg TCDD TEQs can be taken in daily (60 kg average body weight) without appreciable risk of deleterious effects. The current estimated Canadian daily intake for PCDDs and PCDFs from all sources is 2.0-4.2 pg TCDD TEQ5/kg body wt/day (Gilman et al., Chemosphere 23, 1661-1667, 1990). Recent comprehensive epidemiological studies involving industrial/occupational scenarios suggest an increased cancer risk for workers exposed to TCDD-contaminated processes (products contaminated with TCDD) but only at relatively high exposure levels with long latency periods when compared to the background population. To date, the only sustained toxic effect in humans associated with PCDD/PCDF exposure has been chloracne and related dermatological lesions.

Indexes of Obesity and All-Causes Mortality in Italian Epidemiologic Data

Background. The relationships of body mass index and skinfold thickness to all-causes mortality during a 10-year follow-up were assessed in 8,341 men and 1,100 women ages 30–69 years from different Italian population samples. Results. Among men, both univariate and multivariate analyses showed a clear-cut parabolic (inverse J-shaped) relationship, whose left branch became less steep after the exclusion of smokers, people carrying severe diseases at entry, those who died during the first 5 years, or all of them. The minimum risk was almost always located around 28 units of body mass index, and it decreased to smaller levels of body mass index when the exclusions were adopted. The analysis of skinfold thickness showed similar but less clear-cut results. Among women, due to the limited number of fatal events, the analysis was unable to show any clear relationship of body mass index or skinfold thickness to all-causes mortality. The multivariate analysis showed a similar parabolic relationship of body mass index to all-causes mortality. The estimated multivariate risk of death broken down into five quintiles was unrelated to the mean level of body mass index for each quintile. From the multivariate model it was estimated that an excess of 10 kg in body weight (above the body mass index corresponding to the minimum risk level and everything else being equal) carries the same excess of risk produced by 5 mm Hg of systolic blood pressure or by less than 5 cigarettes smoked per day. Conclusion. These results suggest that high levels of obesity indicators are only slightly associated with an excess mortality and that overweight and obesity are health hazards only if they are accompanied by an elevation of other risk factors, mainly of blood pressure.

Return-Risk Analysis of Adopting Drip Irrigation

A return-risk analysis examined the adoption of drip irrigation on expected returns and risk for fresh vegetable enterprises. A risk model (Target MOTAD) determined the return-risk relationships of producing fresh vegetables using southwest Florida yield, market price, and cost data. The model objective was to maximize the expected return from fresh vegetable enterprises subject to a given minimum level of risk associated with a predetermined target level of return. Seven single and eight double- cropped enterprises were evaluated using semi-closed subirrigation and drip irrigation systems. Adoption of the drip irrigation system for the single- and double-cropped production alternatives resulted in lower levels of expected returns and higher levels of risk. The double-cropped alternative resulted in substantially larger expected return values, while risk values were more variable. Examination of the production mix revealed several vegetable enterprises entering the optimal solution at minimum levels of risk. One vegetable crop, tomatoes, was associated with the highest level of risk. Operating capital requirements were substantially higher for double-cropped production compared to the single-cropped alternative.

Computerized systems for high-level information processing and decision-making in PSA

Abstract Probabilistic Safety Assessment (PSA) supports and extends the so-called deterministic approach. PSA is not only useful for the design and construction of large and complex systems like nuclear power plants, but is additionally suitable for the optimization of the operational regimes of a given plant. The evaluation of the high-level information processing and data management in a PSA is made possible as a result of the increased computer performance and comprehensive computer programs as illustrated and discussed in this paper. Special attention is given to the PC specific evaluation because the realization of new developments in the context of PSA has been performed to a continuously increasing extent on Personal Computers (PCs) during the last years. Some detailed descriptions and test results of PC software used for fault tree analysis are shown. Concluding, a PSA—based on the best available information processing tools—is highlighted as the only promising process to design and operate large systems with regard to a minimal risk level.