Oxygen Deficiency Hazard Research Articles

Pressure safety approach for PIP-II cryogenic distribution system and cryomodules

The Proton Improvement Plan-II (PIP-II) is a superconducting linear accelerator being built at Fermilab that will provide 800 MeV proton beam for neutrino production. The linac consists of a total of twenty-three (23) cryomodules of five (5) different types. Cooling is required at 2K, 5K and 40K. The Cryogenic Distribution System (CDS) consists of a Distribution Valve Box, ~285 m of cryogenic transfer line, modular Bayonet Cans to interface with cryomodules, and a Turnaround Can. The cryogenic system must provide protection from over-pressure by sizing pressure relief devices for all volumes and process line circuits. The cryomodule cavity circuits have dual pressure ratings, 4.1 bara when cold and 2.05 bara when warm (T>80K). Worst case relieving cases will be identified. The methods for determining heat flux will be presented. For the relieving occurring in the linac tunnel, flow must vent to outside to avoid an oxygen deficiency hazard. Also, we will present vacuum vessel relief sizing to protect the cryogenic distribution system vacuum shells from over pressure during an internal line rupture. The project is funded by US DOE Offices of Science, High Energy Physics.

Cryogenic oxygen deficiency hazard assessment at the National Synchrotron Radiation Research Center

The National Synchrotron Radiation Research Center (NSRRC) uses cryogenic fluids to create a low-temperature cooling environment for equipment and to conduct various experiments. However, exposure to these cryogenic fluids can cause frostbite, hypoxic suffocation, behavioral incapacitation, insanity, and even death in severe cases. To evaluate oxygen deficiency hazard (ODH) in the NSRRC, we adopted the Fermilab assessment methodology and conducted ODH assessments in the Cryogenic Compressor Room, Taiwan Light Source (TLS) Tunnel, and TLS15A hutch. The results of the evaluation of the Cryogenic Compressor Room and TLS Tunnel revealed that the ODH class is 0 both when the exhaust fan is operating normally and when the exhaust fan is damaged. The exhaust equipment in the TLS15A hutch is only for emergency use. Without the emergency exhaust fan, the ODH class in the area is 1. If the emergency exhaust fan is always on, the ODH class is 0. Therefore, we recommend that those in TLS15A should undergo safety education and receive hazard notifications. In addition, we strongly recommend installing oxygen detectors in the beamline hutch to ensure safety.

The Study on the Quench Helium Release Process of HFRS Superconducting Magnet

The quench phenomenon of the accelerator superconducting magnet may occur in operation, which will cause the liquid helium in the cryostat to evaporate rapidly and release in the atmosphere. High-pressure helium will result in serious damage on significant components in the transmission line, and the released helium in the tunnel will lead to the ODH (Oxygen Deficiency Hazard), threatening the safety of operators. In this paper, the species transport model was used to study the 2D helium discharge process of fragmentation separator in HIAF (High-Intensity heavy-ion Accelerator Facility) by using the platform of computational fluid dynamics software FLUENT. To verify the effectiveness of the species transport model for the FLUENT in simulating the mixing jet process of different components, a 2D FLUENT simulation results of the LHC helium release process was compared with the experimental results and the 3D OpenFOAM simulation results. The results show that the species transport model based on FLUENT could predict the helium release process effectively. Then the distributions of helium concentration, temperature, and velocity in the HFRS (High energy FRagment Separator) tunnel were studied and obtained by the present work. Based on the above analysis, a reasonable design scheme of the accelerator superconducting magnet relief system can be accomplished for HFRS.

ProMetaUS: A proactive meta-learning uncertainty-based framework to select models for Dynamic Risk Management

Safety managers, practitioners, and researchers can employ different models for estimating and assessing hazards, consequences, likelihoods, risks, and/or mitigation measures in the safety field. The selection of a specific model may depend on the uncertainty associated with its estimation and its impact on the safety-related decision-making process. The recognition of this issue as an example of Algorithm Selection Problem (ASP) allows investigating the applicability of meta-learning principles that are scarcely adopted in the risk and safety literature. Consequently, we propose a novel meta-learning inspired framework to proactively rank a set of candidate models for Dynamic Risk Management (DRM) based on desired uncertainty conditions. We denominate this framework ProMetaUS (Proactive Meta-learning and Uncertainty-based Selection for dynamic risk management). To achieve this purpose, our meta-learning system acquires knowledge that relates the characteristics extracted both directly and indirectly from datasets (e.g. data-based, domain-based, simple and fast uncertainty-based, simple and fast sensitivity-based meta-features) to some performance measures of the models. Performance measures include confidence information, shape measurable quantities, safety decision criteria and threshold limits, and sensitivity analysis outputs. We tested the proposed framework in a case study about Oxygen Deficiency Hazard (ODH) assessment by means of @RISK. For each of the five datasets, single-performance measure rankings and a final ranking of the three models are generated. Such rankings are aggregated to obtain the global recommended ranking.

A traditional Near Field-Far Field approach-based model and a spreadsheet workbook to manage Oxygen Deficiency Hazard

Oxygen Deficiency Hazard (ODH) poses a serious occupational risk, and represents a frequent cause of incidents, accidents, and fatalities, mostly in confined spaces and laboratories. Besides these working environments, there is a large spectrum of industries that need to manage the asphyxiation risk caused by extensive inert gas uses. In such a context, mathematical models represent a valuable tool for characterising exposure profiles under varying conditions and evaluating several exposure scenarios, prospectively or retrospectively, for new processes and/or non-routine events. To this end, the objectives of this paper are to: (1) define a traditional Near Field-Far Field (NF-FF) model to estimate the indoor oxygen (O2) concentration percent by volume and partial pressure, and (2) develop a spreadsheet workbook, called ODHMOD, for supporting occupational hygienists, safety and health practitioners, and risk assessors during ODH assessments. Both the NF-FF model and ODHMOD employ data and information usually available in companies, and predict the O2 levels time trends in working environments where inert gas releases can occur, and forced and natural ventilation can move airflows inside and/or outside. The mathematical model and its implementation in Microsoft® Excel are described, with an example of its application in a possible industrial scenario.

Oxygen deficiency hazard in confined spaces in the steel industry: assessment through predictive models

Objective. In the steel industry, performing activities in confined spaces where potential oxygen displacement can occur may expose workers to fatal consequences. To the best of our knowledge, no quantitative exposure assessment of oxygen deficiency in steel industry confined spaces is available in the literature. To overcome this gap, we performed oxygen deficiency hazard (ODH) assessments in real confined spaces using two existing models to identify the most critical parameters responsible for ODH, and suggest controls for mitigating the asphyxiation risk. Methods. We applied a well-mixed model and a near field–far field approach to estimate the indoor oxygen level with time during and following release of simple asphyxiants. Model inputs were mainly gathered thanks to audits and instrumental tests in three firms. Results. The most severe ODH exposures are posed in spaces with restricted volume and where accidental releases of inert gases can occur. Such exposures can be controlled through early release detections and augmented reality systems. Conclusions. ODH assessments in confined spaces of steel firms allow the identification of the most critical parameters from an oxygen depletion perspective, focusing on which data need careful measurement, and help to establish controls compatible with the operations conducted in these areas.

Numerical investigation of potential stratification caused by a cryogenic helium spill inside a tunnel

The sudden release of cryogenic fluid into an accelerator tunnel can pose a significant health and safety risk. For this reason, it is important to evaluate the consequences of such a spill. Previous publications concentrated on either Oxygen Deficiency Hazard or the evaluation of mathematical models using experimental data. No studies to date have focussed on the influence of cryogen inlet conditions on flow development. In this paper, the stratification behaviour of low-temperature helium released into an air-filled accelerator tunnel is investigated for varying helium inlet diameters. A numerical model was constructed using the OpenFOAM Toolbox of a generalised 3D geometry, with similar hydraulic characteristics to the CERN and SLAC tunnels. This model has been validated against published experimental and numerical data. A dimensionless parameter, based on Bakke number, was then determined for the onset of stratification, taking into account the helium inlet diameter; a dimensionless parameter for the degree of stratification was also employed. The simulated flow behaviour is described in terms of these dimensionless parameters, as well as the temperature and oxygen concentration at various heights throughout the tunnel.

Cryogenic safety in helium cryostats at CERN

Cryostats contain large cold surfaces, cryogenic fluids, and sometimes large stored energy (e.g. energized magnets), with the potential risk of sudden liberation of energy through thermodynamic transformations of the fluids, which can be uncontrolled and lead to a dangerous increase of pressure inside the cryostat envelopes. The consequence, in the case of a rupture of the envelopes, may be serious for personnel (injuries from deflagration, burns, and oxygen deficiency hazard) as well as for the equipment. Performing a thorough risk analysis is an essential step to identify and understand risk hazards that may cause a pressure increase and in order to assess consequences, define mitigation actions, and design adequate safety relief devices to limit pressure accordingly. Lessons learnt from real cases are essential for improving safety awareness for future projects. We cover in this paper our experience on cryostats at CERN and the design-for-safety rules in place.

Safety aspects of whole-body cryochamber and cryosauna operation

Interest in low temperature treatment is constantly increasing. Whole-body cryotherapy (WBC) devices are becoming available not only in medical centers but also in local gyms and spa centers. A new group of users are professional sport clubs where 3-minutes session of whole-body cryotherapy is post-training procedure to improve and speed up the recovery process. There are four different types of WBC devices available on the market and offered to commercial (non-medical) users. The American and European market is dominated by two of them: classic cryochambers and cryosaunas. Both constructions are supplied with liquid nitrogen. Low temperature inside classic cryochamber is produced by evaporating of liquid nitrogen in two or more heat exchangers. There is never a direct contact between user and cryogenic medium in any of system operation mode (closed supply system). Cryosauna is cooled down by filling with cold vapor of liquid nitrogen. Supply system is considered open because it allows for direct contact between user and cryogenic medium. Open supply system of cryosauna is primary and most questionable issue of its operational safety, particularly after tragic accident in October 2015. This paper presents the comparative analysis of classic cryochamber and cryosauna from safety point of view. Both devices have been analyzes and tested on existing systems in operation. Paper gives detailed analysis of constructions, supply systems and working parameters. Special attention has been focused to problem of oxygen deficiency hazard. Different failure or accident scenarios have been analyzed and discussed.

A Near Field–Far Field model for assessing Oxygen Deficiency Hazard

Oxygen Deficiency Hazard (ODH) due to inert gas releases can be assessed by the use of predictive models. Several models are available in the literature: the majority of them can be classified as “well-mixed” models because they assume the existence of completely and instantaneously well mixed air. In order to provide a more precise estimation of the indoor oxygen level in the breathable air close to a release point, we propose a Near Field–Far Field (NF–FF) model in which the Near Field volume is an output and can vary over time. The trend of the Near Field size can be a useful data for the risk assessor in order to determine the safety distance from point source releases, and improve the emergency response plan. Starting from balances of mass of air and moles of oxygen both in the Near Field and in the Far Field, the objective of our model is to predict the volume of the Near Field that contains a limit value for the oxygen concentration at every time instant. The approach includes several analytical formulas that model the different flows occurring in each field and between the two fields. In particular, we assume the existence of inert gas releases, forced and natural ventilation airflows, interzonal airflows, and air that has to move from the Far Field to the Near Field, or vice versa, for assuring a limit value for the oxygen concentration in the Near Field. Finally, examples of the application of this model in some case studies available in the literature are presented and discussed.

A predictive model for estimating the indoor oxygen level and assessing Oxygen Deficiency Hazard (ODH)

In some working environments there may be Oxygen Deficiency Hazard (ODH) when workers are exposed to a low indoor oxygen level. This hazard can be assessed applying a predictive model. In the literature, there are sixteen models estimating the oxygen content subsequent to releases of inert gases. These models present several weaknesses, such as the rarity of consideration of accidental releases, of Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) systems reliability, and of the existence of both forced and natural ventilation. For overcoming these weaknesses, we propose a new predictive model for assessing ODH caused by voluntary or accidental releases of inert gases. Our model is based on the balances of mass of air and of moles of oxygen. Our model fills some gaps identified in the literature models (e.g. the estimation of natural ventilation, infiltration, and exfiltration), and allows the identification of those parameters responsible for ODH. In order to evaluate our model, we have performed several simulation tests. We have obtained that our results are comparable to the outputs of some case studies available in the literature, and we have analysed the effects of some new aspects of the model. The model represents a helpful tool to implement in any working environment where ODH has to be assessed.

Partial inerting – A possible means of eliminating the brush-discharge-ignition hazard with explosive gases and vapours?

It was found that the brush discharge ignition hazard with IIA gases/vapours (propane) can be eliminated by reducing the oxygen/nitrogen volume ratio in the atmosphere to the order of 15/85. The condition is that the diameter of the earthed electrode ≤ 40 mm. Published information on whether an oxygen/nitrogen ratio of 15/85 is acceptable as regards the oxygen deficiency hazards is contradictory. With IIB gases/vapours (ethylene) the oxygen/nitrogen ratio must be reduced to at least 10/90 to eliminate the brush-discharge-ignition hazard. Lowering the oxygen/nitrogen ratio to this level will undoubtedly present a substantial oxygen deficiency hazard to humans. ► Brush discharge ignition of IIA gases can be eliminated if the O 2 /N 2 volume ratio is reduced to ≤15/85. ► The condition is that radii of curvature of earthed electrodes ≤20 mm. ► Whether or not this is acceptable in terms of oxygen deficiency hazards to humans is unclear. ► With IIB gases an O 2 /N 2 ratio << 15/85 is required for eliminating the brush discharge ignition hazard. ► When assessing the brush discharge ignition hazard all MIEs must be determined by identical methods.

Ultrasonic helium detectors applied in oxygen deficiency hazard monitor system in radiation environment

The prototype ultrasonic sound velocity measuring system was designed and built at Wroclaw University of Technology. The system aims to detect helium release into the air in a quantity that may cause oxygen deficiency hazard (ODH) and is also dedicated to work in radiation conditions. In order to qualify the measuring system to be used in accelerator tunnels, the stability of the readouts and the durability of the ultrasonic transducers and electronics have been investigated in a radiation environment. Two tests were carried out: one at the European Organization for Nuclear Research CERN in Geneva, and another at the Institute of Atomic Energy (IEA) in Otwock-Swierk near Warsaw, Poland. The readouts were very stable and there was no danger of provoking false alarms of ODH. The accumulated doses absorbed by the system correspond to over 10 years of the large hadron collider (LHC) operation. The developed technology can be considered being used in installations where the oxygen deficiency hazard may be a result of helium release into the air, especially in particle accelerators where the measuring system is threatened by ionizing radiation.

Safety oriented analysis of cold helium–air mixture formation and stratification

Cryogenic installations of superconducting accelerators contain significant amount of high density helium, mostly filling the cryostats and headers located in underground tunnels and caverns. In the case of emergency relief of the helium, oxygen deficiency hazard arises. The paper proposes a description of helium–air mixture formation based on turbulent jet physics. A condition of stratified flow onset is given resulting from dimensional analysis. A performed experiment of cold helium discharge to an instrumented test tunnel enabled identification of different stratified flow types together with corresponding measurements of oxygen concentration and temperature drop. The results can be used for safety analysis of oxygen deficiency hazard in confined areas, especially in the tunnels.

Oxygen Deficiency Hazard Induced by Helium Release in Accelerator Tunnel

Tests to investigate oxygen deficiency levels due to release of helium into the CBA tunnel are described. Results of the tests indicate that the helium stratifies and spreads quickly in the horizontal plane. This demonstrates that adequate warning of possible asphyxiation hazards can be achieved. When oxygen deficiency monitors are located at ceiling level they may be spaced at intervals of 60 m. or more and still achieve acceptable results.