Reasonable Worst Case Research Articles

Compilation method of a catalogue of reasonable worst-case rainfall series for flash flood simulations of short, convective rainstorms

In this study, a categorisation method was developed and applied to identify, select and rank reasonable worst-case rainfall storm events with time-series resolution of one minute and duration of up to one hour. The method yields a catalogue of 24 reasonable worst-case rainfall series, i.e. potentially catastrophic events that could be used for safe-to-fail flash flood model scenarios, thus encouraging the testing of critical infrastructure and pedestrian safety for people trapped in floods. The identified 24 events were shown to be considerably more extreme than corresponding design storms, with a return interval of 100 years. In the selection of the extremes, special care was taken to consider different hazard attributes, which are associated with intrinsically different observed hyetograph shapes, including rectangular, short and long triangle, and double peak shape categories. Hydrodynamic simulations were carried out using the 2D robust shallow water model hms++ to quantify the flooding impact of the 24 rainfall scenarios in a small urbanised catchment, which enabled the ranking of the scenarios based on different hazard attributes. Overall, the rectangular and long-triangle events showed the highest total discharge, and the rectangular events comprise both the longest duration for hazard velocity and deep flooding. The long-triangle events presented the highest peak discharge and peak water depths. The short-triangle ones showed the highest flashiness (shortest time to peak), whereas the double peak events yielded the longest time to peak. The ranking emphasised the importance of the hyetograph shape characteristics of extreme storms and which needs to be taken into account in flash flood management. The novel categorisation method is easily transferable to other regions, if high-resolution rain series are available.

Characterization modeling of wake vortex circulation decay under reasonable worst case conditions with cuckoo search algorithm

Wake vortex (WV) produced by a large aircraft has the potential to cause serious damage to smaller aircraft following it. In this context, characterization of WV circulation decay under the reasonable worst case (RWC) conditions allows the separation minima to be found safely. In this study, modeling of dimensionless decay curves, which were developed using three experimental LIDAR (Light Detection and Ranging) datasets in the RECAT-EU project and is a useful tool to characterize the wake vortex circulation decay under RWC conditions, was carried out using cuckoo search algorithm (CSA). The decay curves used in the modeling are the median (P50), 10th (P10), and 90th (P90) percentile decay curves of the RWC tracks, which constitute the top 2% longest lasting wakes. The fact that the correlation coefficient (R) values are very close to 1 for all datasets as a result of the error analysis shows that the prediction success of the CSA model is quite high.

Corium pool behaviour in the core catcher of a sodium-cooled fast reactor

Within the framework of the severe accident mitigation strategy for GEN-IV reactors, the behaviour of molten corium in the SFR core catcher is a subject of significant interest. This article aims to define the main considerations within the core catcher during a prospective severe accident scenario, in particular with regard to the rate of heat transfer to the core catcher structures. On the basis of the core catcher design adopted at the end of the ASTRID project, a simplified model is proposed to conservatively evaluate the quasi-steady state behaviour in a stratified oxide-metal molten corium pool with mechanically stable crusts at the interfaces between the stratified layers and at the core catcher walls. The corium oxide layer is subject to significant internal heat generation due to the radioactive decay heat. The proposed model implies that the core catcher should withstand reasonable worst case estimates for the thermal load from the corium pool, avoiding sodium boiling and thermal ablation of the core catcher structures. Thermal ablation is only predicted in the cases of an order of magnitude under-prediction of the heat transfer coefficients at the lateral boundary of the corium oxide layer, or for local heat flux values in excess of 3.7 times the surface average. Further investigations will be dedicated to the revision of the more conservative model assumptions, in particular regarding the magnitude of the heat flux from high aspect ratio encloses with large internal Rayleigh numbers. A refined transient version of the model is intended for implementation within the PROCOR platform developed by the CEA.

Quantifying Emission Factors and Setting Conditions of Use According to ECHA Chapter R.14 for a Spray Process Designed for Nanocoatings-A Case Study.

Spray coatings’ emissions impact to the environmental and occupational exposure were studied in a pilot-plant. Concentrations were measured inside the spray chamber and at the work room in Near-Field (NF) and Far-Field (FF) and mass flows were analyzed using a mechanistic model. The coating was performed in a ventilated chamber by spraying titanium dioxide doped with nitrogen (TiO2N) and silver capped by hydroxyethylcellulose (Ag-HEC) nanoparticles (NPs). Process emission rates to workplace, air, and outdoor air were characterized according to process parameters, which were used to assess emission factors. Full-scale production exposure potential was estimated under reasonable worst-case (RWC) conditions. The measured TiO2-N and Ag-HEC concentrations were 40.9 TiO2-μg/m3 and 0.4 Ag-μg/m3 at NF (total fraction). Under simulated RWC conditions with precautionary emission rate estimates, the worker’s 95th percentile 8-h exposure was ≤171 TiO2 and ≤1.9 Ag-μg/m3 (total fraction). Environmental emissions via local ventilation (LEV) exhaust were ca. 35 and 140 mg-NP/g-NP, for TiO2-N and Ag-HEC, respectively. Under current situation, the exposure was adequately controlled. However, under full scale production with continuous process workers exposure should be evaluated with personal sampling if recommended occupational exposure levels for nanosized TiO2 and Ag are followed for risk management.

Plate lines to enhance wake vortex decay for reduced separations between landing aircraft

To mitigate the risk of wake vortex encounters during final approach, so-called plate lines have been developed. Data collected during a six-month measurement campaign at Vienna International Airport are used to assess the potential for reducing minimum aircraft separations facilitated by plate lines during approach and landing following the re-categorisation (RECAT-EU) methodology for revised wake turbulence categorisation. To ensure that no other parameters controlling wake vortex decay bias the analysis, it is verified that wind speed, atmospheric turbulence, thermal stratification and flight altitude reside in similar ranges with and without the plates. The analysis follows the steps of the RECAT-EU method to generate non-dimensional so-called reasonable worst-case circulation decay curves; one as a reference for nominal operations without plates and one representing the accelerated wake vortex decay brought about by the plate lines. The difference between the two circulation decay curves corresponds to the non-dimensional time-based aircraft separation reduction potential that can be translated into distance-based separation gains. Depending on the particular RECAT-EU category combination, the attained aircraft separation reduction potential ranges between 12% and 15%. Constricting the analysis to wake vortices generated by one aircraft type representing the Upper Heavy RECAT-EU category, the separation reduction potential amounts up to 24%.

Cleaning product emissions and indoor built environments: Exposure and health risk assessments from experiments under realistic indoor conditions

Cleaning products are among the most widely used consumer products. The associated risks should be better understood. The health risk assessment (HRA) approach was applied to household uses of cleaning products, with nineteen products of various types and formats tested under typical indoor environmental parameters in an experimental house. The targeted substances included volatile organic compounds (VOCs) and carbonyl compounds. The generic “Common Use” and “Reasonable Worst-Case” scenarios under consideration were based on full cleaning sessions. These sessions were elaborated from data available in the technical and scientific literature, combined with stakeholder participation. The Common Use scenario included a 1 1/2-h cleaning session once per week, followed by manual ventilation; the Reasonable Worst-Case scenario included a 4-h session twice per week without manual ventilation. No situation of concern was found regarding chronic inhalation exposures associated with Common Use. For the Reasonable Worst-Case scenario, the assessed chronic inhalation risks were low. Assessed acute inhalation exposures (1-h exposures) could exceed the selected health values, mainly for acrolein (exposures up to 12 μg/m3) and formaldehyde (exposures up to ∼140 μg/m3). Associated first observed effects could include nasal, throat, and eye irritation. These results suggest that the highest exposures should be reduced and, to this end, that the emissions of the most emissive products should be reduced. Since the identified priority substances of concern are not specific to cleaning product emissions, multisource cumulative exposures are expected with the use of other consumer products, e.g., paints, incense, scented candles, furniture, and fragrance diffusers.

Science and policy in extremis: the UK’s initial response to COVID-19

Drawing on the SAGE minutes and other documents, I consider the wider lessons for norms of scientific advising that can be learned from the UK’s initial response to coronavirus in the period January–March 2020, when an initial strategy that planned to avoid total suppression of transmission was abruptly replaced by an aggressive suppression strategy. I introduce a distinction between “normatively light advice”, in which no specific policy option is recommended, and “normatively heavy advice” that does make an explicit recommendation. I argue that, although scientific advisers should avoid normatively heavy advice in normal times in order to facilitate democratic accountability, this norm can be permissibly overridden in situations of grave emergency. SAGE’s major mistake in early 2020 was not that of endorsing a particular strategy, nor that of being insufficiently precautionary, but that of relying too heavily on a specific set of “reasonable worst-case” planning assumptions. I formulate some proposals that assign a more circumscribed role to “worst-case” thinking in emergency planning. In an epilogue, I consider what the implications of my proposals would have been for the UK’s response to the “second wave” of late 2020.

RMetS Meteorological Masterclass Series: Anticipating floods, droughts and heatwaves

<scp>RMetS M</scp>eteorological <scp>M</scp>asterclass <scp>S</scp>eries: Anticipating floods, droughts and heatwaves

Assessment of exposure determinants and exposure levels by using stationary concentration measurements and a probabilistic near-field/far-field exposure model.

Background: The Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulation requires the establishment of Conditions of Use (CoU) for all exposure scenarios to ensure good communication of safe working practices. Setting CoU requires the risk assessment of all relevant Contributing Scenarios (CSs) in the exposure scenario. A new CS has to be created whenever an Operational Condition (OC) is changed, resulting in an excessive number of exposure assessments. An efficient solution is to quantify OC concentrations and to identify reasonable worst-case scenarios with probabilistic exposure modeling. Methods: Here, we appoint CoU for powder pouring during the industrial manufacturing of a paint batch by quantifying OC exposure levels and exposure determinants. The quantification was performed by using stationary measurements and a probabilistic Near-Field/Far-Field (NF/FF) exposure model. Work shift and OC concentration levels were quantified for pouring TiO 2 from big bags and small bags, pouring Micro Mica from small bags, and cleaning. The impact of exposure determinants on NF concentration level was quantified by (1) assessing exposure determinants correlation with the NF exposure level and (2) by performing simulations with different OCs. Results: Emission rate, air mixing between NF and FF and local ventilation were the most relevant exposure determinants affecting NF concentrations. Potentially risky OCs were identified by performing Reasonable Worst Case (RWC) simulations and by comparing the exposure 95 th percentile distribution with 10% of the occupational exposure limit value (OELV). The CS was shown safe except in RWC scenario (ventilation rate from 0.4 to 1.6 1/h, 100 m 3 room, no local ventilation, and NF ventilation of 1.6 m 3/min). Conclusions: The CoU assessment was considered to comply with European Chemicals Agency (ECHA) legislation and EN 689 exposure assessment strategy for testing compliance with OEL values. One RWC scenario would require measurements since the exposure level was 12.5% of the OELV.

Outbreaks in care homes may lead to substantial disease burden if not mitigated.

The number of COVID-19 outbreaks reported in UK care homes rose rapidly in early March of 2020. Owing to the increased co-morbidities and therefore worse COVID-19 outcomes for care home residents, it is important that we understand this increase and its future implications. We demonstrate the use of an SIS model where each nursing home is an infective unit capable of either being susceptible to an outbreak (S) or in an active outbreak (I). We use a generalized additive model to approximate the trend in growth rate of outbreaks in care homes and find the fit to be improved in a model where the growth rate is proportional to the number of current care home outbreaks compared with a model with a constant growth rate. Using parameters found from the outbreak-dependent growth rate, we predict a 73% prevalence of outbreaks in UK care homes without intervention as a reasonable worst-case planning assumption.This article is part of the theme issue ‘Modelling that shaped the early COVID-19 pandemic response in the UK’.

Household cooking oil use and its bearing on fire safety

Cooking oil fires present a reasonable worst-case hazard when considering thermal radiation to occupants close to a kitchen hob/cooktop. Shallow or deep frying, the activity frequency and the oil volume may contribute to the risk. A review of cooking oil use is presented via consumer purchasing habits, studies on the health effects of cooking with oil and statistics related to the disposal of cooking oil waste. An online survey provides further data on current cooking practices. Olive oil, vegetable oil or pure sunflower appear to be the most common types. Results suggest that cooking on a hob occurs 4 times per month for deep frying and 17 times per month for shallow frying. A design value of 250 mL is advocated for all frying activities with a frequency of 11 times per month. Design volumes of 2.5 L and 150 mL are proposed for deep and shallow frying, respectively.

Following the Science: Pandemic Policy Making and Reasonable Worst-Case Scenarios

The UK has been ‘following the science’ in response to the COVID-19 pandemic in line with the national framework for the use of scientific advice in assessment of risk. We argue that the way in which it does so is unsatisfactory in two important respects. Firstly, pandemic policy making is not based on a comprehensive assessment of policy impacts. And secondly, the focus on reasonable worst-case scenarios as a way of managing uncertainty results in a loss of decision-relevant information and does not provide a coherent basis for policy making.

Developing a regulatory framework for certifying spill management teams in California: a balancing act

ABSTRACT 1141476 Major oil spills in California have historically instigated legislation aimed at improving preparedness and response. Most recently, public concern over management of high-profile pipeline spills precipitated the 2017 passage of Assembly Bill (AB) 1197, which mandated a certification program for spill management teams (SMTs). AB 1197 directs contingency plan holders to identify a certified SMT capable of managing their reasonable worst-case spill (RWCS) volumes, and tasks the Office of Spill Prevention and Response (OSPR) with adopting regulations establishing criteria for certification, including personnel on-scene times, training, and response objectives. We aimed to develop regulations detailing requirements that are achievable, but effectively advance preparedness, drawing upon accepted standards while incorporating mechanisms for flexibility. As we developed the regulations, we conducted informal scoping meetings with industry to fine-tune these mechanisms. We created three tiers for certification delineated by RWCS volume. To account for phased resource mobilization, we established separate requirements for initial response and cascading SMT personnel. We applied team-based training requirements to initial responders and used pared-down National Incident Management System qualifications for cascading personnel, allowing equivalent courses and/or experience to substitute for required training courses. We composed a short objectives checklist, aiming to capture essential tasks to be completed within the first 24 hours. The final regulatory package strikes balances between flexibility and prescription, and between achievability and advancing statewide preparedness.

Economic feasibility of flexible energy productions by small modular reactors from the perspective of integrated planning

Nuclear power plants are known as low carbon baseload electricity generating options, but can they become sufficiently flexible to follow the fluctuating demand economically? Small modular reactors, conceived to address the issues associated with large sized nuclear reactors such as safety, costs, and completion timeline, can offer some flexibility through modularity. However, there remain the questions of whether and how these advanced concepts could become commercially viable for load-following electricity production. From the perspective of integrated long-term energy planning and in a scenario-based approach, this study is conceived to evaluate the economic feasibility of flexible energy productions from two first-of-a-kind demonstration projects; namely a floating nuclear power plant KLT-40S in Russia and a high temperature reactor pebble-bed module or HTR-PM in China. Although both projects are solely designed for electric-application, this study proposes the evaluation of a load-following arrangement through the co-production of hydrogen and the integration of grid-connected battery energy storage systems. All scenarios are investigated using a conservative or a reasonable worst-case approach so as to contribute to setting the bottom line for future commercial deployment of small modular reactors. Findings suggest that small modular reactors can already be commercially deployed in the short-to mid-term, and there are opportunities for further cost reductions through technological innovation and economies of repeat project implementation.

Modeling of VOCs and criteria pollutants from multiple natural gas well pads in close proximity, for different terrain conditions: A Barnett Shale case study

Despite potential advantages in spatial/temporal coverage compared to measurement studies, few modeling studies have been conducted of non-methane air pollutants associated with natural gas. The objective of this study was to model volatile organic compound (VOC) and criteria pollutants from natural gas production, considering multiple well pads under different terrain conditions, using the Texas Barnett Shale as a case study.Primary criteria pollutants from compressor engines (carbon monoxide, CO; nitrogen oxides, NOx; particulate matter, PM10; sulfur dioxide, SO2) were modeled using AERMOD, along with benzene as a VOC with potential worst health impacts, from condensate tanks, fugitive sources, and compressor engines. Modeling was conducted for level, moderate, and strong sloping terrain, with well pad densities of 1.4–1.9 well pads/km2, exemplifying common maximum densities in the Barnett Shale.In most cases, well pads were far enough away from each other that maxima at individual well pads were not influenced by other pads. When the same well pad arrangement and emission rates were modeled in different terrain types, strong sloping terrain gave the highest maximum concentrations.For the well pad arrangements and emission scenarios modeled, CO, NOx, PM10, and SO2 maximum concentrations were less than the 1-h National Ambient Air Quality Standards (NAAQS). Benzene concentrations, however, exceeded the 1-h effect screening level (ESL) for level and strong sloped terrain, and the annual ESL for all terrain types. The maximum benzene emissions modeled likely represent a reasonable worst-case for the Barnett Shale but underestimate emissions for areas with wetter gas.

Key Design Elements of Building Pressure Cycling for Evaluating Vapor Intrusion-A Literature Review.

Building pressure cycling (BPC) is becoming an increasingly important tool for studying vapor intrusion. BPC has been used to distinguish subslab and indoor sources of vapor intrusion as well as to define reasonable worst case volatile organic compound mass discharge into a structure. Analyses have been performed both semi-quantitatively with concentration trends and quantitatively with more rigorous flux calculation and source attribution methods. This paper reviews and compares the protocols and outcomes from multiple published applications of this technology to define the key variables that control performance. Common lessons learned are identified, including those that help define the range of building size and type to which BPC is applicable. Differences in test protocols are discussed, recognizing that the complexity of the test protocol required depends on the particular objectives of each project. Research gaps are identified and tabulated for future validation studies and applications.

Evaluation of Exposure Assessment Tools under REACH: Part II-Higher Tier Tools.

Stoffenmanager®v4.5 and Advanced REACH Tool (ART) v1.5, two higher tier exposure assessment tools for use under REACH, were evaluated by determining accuracy and robustness. A total of 282 exposure measurements from 51 exposure situations (ESs) were collected and categorized by exposure category. In this study, only the results of liquids with vapor pressure (VP) > 10 Pa category having a sufficient number of exposure measurements (n = 251 with 42 ESs) were utilized. In addition, the results were presented by handling/activity description and input parameters for the same exposure category. It should be noted that the performance results of Stoffenmanager and ART in this study cannot be directly compared for some ESs because ART allows a combination of up to four subtasks (and nonexposed periods) to be included, whereas the database for Stoffenmanager, separately developed under the permission of the legal owner of Stoffenmanager, permits the use of only one task to predict exposure estimates. Thus, it would be most appropriate to compare full-shift measurements against ART predictions (full shift including nonexposed periods) and task-based measurements against task-based Stoffenmanager predictions. For liquids with VP > 10 Pa category, Stoffenmanager®v4.5 appeared to be reasonably accurate and robust when predicting exposures [percentage of measurements exceeding the tool's 90th percentile estimate (%M > T) was 15%]. Areas that could potentially be improved include ESs involving the task of handling of liquids on large surfaces or large work pieces, allocation of high and medium VP inputs, and absence of local exhaust ventilation input. Although the ART's median predictions appeared to be reasonably accurate for liquids with VP > 10 Pa, the %M > T for the 90th percentile estimates was 41%, indicating that variance in exposure levels is underestimated by ART. The %M > T using the estimates of the upper value of 90% confidence interval (CI) of the 90th percentile estimate (UCI90) was considerably reduced to 18% for liquids with VP > 10 Pa. On the basis of this observation, users might be to consider using the upper limit value of 90% CI of the 90th percentile estimate for predicting reasonable worst case situations. Nevertheless, for some activities and input parameters, ART still shows areas to be improved. Hence, it is suggested that ART developers review the assumptions in relation to exposure variability within the tool, toward improving the tool performance in estimating percentile exposure levels. In addition, for both tools, only some handling/activity descriptions and input parameters were considered. Thus, further validation studies are still necessary.

Comparison of the near field/far field model and the advanced reach tool (ART) model V1.5: exposure estimates to benzene during parts washing with mineral spirits.

The Advanced Reach Tool V1.5 (ART) is a mathematical model for occupational exposures conceptually based on, but implemented differently than, the "classic" Near Field/Far Field (NF/FF) exposure model. The NF/FF model conceptualizes two distinct exposure "zones"; the near field, within approximately 1m of the breathing zone, and the far field, consisting of the rest of the room in which the exposure occurs. ART has been reported to provide "realistic and reasonable worst case" estimates of the exposure distribution. In this study, benzene exposure during the use of a metal parts washer was modeled using ART V1.5, and compared to actual measured workers samples and to NF/FF model results from three previous studies. Next, the exposure concentrations expected to be exceeded 25%, 10% and 5% of the time for the exposure scenario were calculated using ART. Lastly, ART exposure estimates were compared with and without Bayesian adjustment. The modeled parts washing benzene exposure scenario included distinct tasks, e.g. spraying, brushing, rinsing and soaking/drying. Because ART can directly incorporate specific types of tasks that are part of the exposure scenario, the present analysis identified each task's determinants of exposure and performance time, thus extending the work of the previous three studies where the process of parts washing was modeled as one event. The ART 50th percentile exposure estimate for benzene (0.425ppm) more closely approximated the reported measured mean value of 0.50ppm than the NF/FF model estimates of 0.33ppm, 0.070ppm or 0.2ppm obtained from other modeling studies of this exposure scenario. The ART model with the Bayesian analysis provided the closest estimate to the measured value (0.50ppm). ART (with Bayesian adjustment) was then used to assess the 75th, the 90th and 95th percentile exposures, predicting that on randomly selected days during this parts washing exposure scenario, 25% of the benzene exposures would be above 0.70ppm; 10% above 0.95ppm; and 5% above 1.15ppm. These exposure estimates at the three different percentiles of the ART exposure distribution refer to the modeled exposure scenario not a specific workplace or worker. This study provides a detailed comparison of modeling tools currently available to occupational hygienists and other exposure assessors. Possible applications are considered.

The BROWSE model for predicting exposures of residents and bystanders to agricultural use of pesticides: Comparison with experimental data and other exposure models

A new suite of models has been developed for assessing the exposure of bystanders, residents, operators and workers to pesticides used in agricultural applications. The aim of these ‘BROWSE’ models was to improve regulatory exposure assessment by including recent data, and changes in current knowledge and application practice. The new models for bystander and resident exposure focused on spray drift from boom and orchard sprayers, and vapour emissions from treated crops. The structure of the resident and bystander models is reported elsewhere, together with a description and discussion of model inputs. This paper describes model outputs, model validation where experimental data are available, a sensitivity analysis for some model components and compares predictions with other European regulatory models, including the recently developed European Food Safety Authority (EFSA) calculator. Because BROWSE models can simulate a range of scenarios, there is a wide range of possible outputs. When using recommended default inputs, the resident and bystander models predict higher exposures than existing regulatory models. This is because the model incorporates more exposure routes and defaults are based on a reasonable worst case scenario. However, the probabilistic nature of the BROWSE models results in lower predicted exposures than the new EFSA calculator. Validation of sections of the model suggests that it is not overly conservative. Sensitivity analysis of the vapour exposure component showed that the interaction between temperature and vapour pressure, which is not taken account of in other models, can result in lower exposures for higher vapour pressures in warmer climates.

Modelling exposure of workers, residents and bystanders to vapour of plant protection products after application to crops

Agricultural use of plant protection products can result in exposure of bystanders, residents, operators and workers. Within the European Union (EU) FP7 project BROWSE, a tool based on a set of models and scenarios has been developed, aiming to assess the risk of exposure of humans to these products. In the present version of the tool only a first conservative tier is available for outdoor vapour exposure assessment.In the vapour exposure evaluation, the target concentrations in air at 10m distance from the edge of a treated field are calculated for specific scenarios for each EU regulatory zone. These scenarios have been selected to represent reasonable worst case volatilisation conditions. The exposure assessment is based on a series of weekly applications in a five year period to cover a wide range of meteorological conditions. The volatilisation from the crop is calculated using the PEARL model and this PEARL output provides the emission strength used as input for the short term version of the atmospheric transport model OPS.The combined PEARL-OPS model is tested against measurements from a field experiment. First results of this test show that the mean concentration level was predicted fairly well. However, sometimes the differences between observations and simulations were found to be substantial. Improvements are suggested for the vapour exposure scenarios as well as for further model development.In the current version of the BROWSE tool a simplified procedure is used to assess single and multiple applications. The actual period of application and the time of application during the day are fixed, and the growth stage of the crop cannot be taken into account. Moreover, competing processes such as penetration of the substance into the plant tissue are not considered. The effect of these factors on the target exposure concentrations is discussed.