Regulations and Standards for Hazardous Gases, Toxic Gases Behaviour, and Wind Effects - Literature review Example

Please check and let me know if I missed anything. Sorry for the delay. I am just having difficulty finding resources. Thanks! Modelling Gas Release Abstract Acknowledgements Contents List of Illustrative Materials Chapter 1: Introduction 1. General Introduction 1.1 Introduction 1.2 Aims and Objectives 1.3 Research Methodology 1.4 Summary of Dissertation 1.5 Main Achievements Chapter 2: Literature Review 2. Literature Review 2.1 Introduction Toxic gases pose particular hazards to the public particularly when they are disperse by the wind because they may cover large areas downwind before they dissipate to safe levels (Fthenakis, 1993:404). These harmful gases may be released at hazardous materials incidents such as leaking storage containers and industrial equipments. It may be also released through decaying organic materials, fire, and other chemical reactions (National Fire Protection Association, 2008:46). Moreover, accidental gas release can lead to short or long-term health effects as in the case of Bhopal Gas Disaster where victims suffered eye, lungs, and gastrointestinal health effects such as acute conjunctivis, coughing, dyspnea, pulmonary oedema, and other chronic damage to the lungs (Havenal et al, 2002:132). Fire can also produce harmful gases that can severely affect the human body and these include hydrogen cyanide, a poisonous gas produce by plastic products and phosgene gas coming from burning household products such a vinyl. These harmful gases are quickly absorbed by the blood and in higher levels can cause pulmonary edema and death. Carbon monoxide is not toxic but it can displace oxygen from the atmosphere and cause asphyxiation during a fire (National Fire Protection Association, 2008:46). Chemical asphyxiants like carbon monoxide, hydrogen sulphide, hydrogen cyanide, and sulphur dioxide can halt oxygen delivery to cells causing death to respiratory arrest (Veasey et al, 2005:39). Unlike solid materials that retain its shape or liquids that take on the shape of their contained, gases immediately disperse and expand to fill spaces that are available to them. Some gases are a lighter than air and carried away by the wind while heavier gases move down and flow downhill into low-elevation areas such as basements, trenches and others (Veasey et al, 2005:39). Since gas in theory has tiny particles that constantly in random motion and free to move in all possible directions, it can behave differently in some circumstances particularly when heated, pressured, and affected by wind direction and speed (Mungai, 2004:1). According to CCPS (2010:77), gas behaviour is dependent not only on release rate but on atmospheric conditions such as wind speed, time of day, cloud cover, and so on. For this reason, gas regardless of buoyancy and density travels along with the wind at the same speed and direction. For instance, dense gas releases will mix and be diluted with fresh air as it travels downwind behaving like neutrally buoyant gas. Release of heavier than air gas may result to high concentration of gas at ground level with tendencies to flow down terrain gradients due to gravity. However, although may be slower than lighter gases, it will eventually mix with the ambient air and flow in the direction of the wind (Murphy & Morrison, 2007:604). 2.2 Accidents involving toxic gases release INSERT CASE STUDIES HERE 2.3 Regulations and Standards for Hazardous Gases Since the Bhopal Disaster in 1984, there seems a common consensus on the potential of toxic gases to cause disaster and kill significant number of people. In Europe for instance, the risk of major accidents associated with toxic gas release are regulated by the Seveso II Directive for the Control of Major Accidental Hazards Involving Dangerous Substances. In UK, the implementation of Seveso II Directive is in the Control of Major Accidents Hazards Regulations 1999 or COMAH while the Hazardous Substances Regulations 1992 regulated land-use in England and Wales (Trainor et al, 2004:1). The primary aim of COMAH is to prevent and mitigate the effects of major accidents involving dangerous substances such as benzene, liquefied petroleum gas or LPG, explosives, nuclear materials, and arsenic pentoxide which can cause serious harm to people and the environment (Maquire, 2012:11). Influenced by the Flixborough chemical plant accident in 1974, COMAH requires operators to prepare MAPP or Major Accident Prevention Policy and comply with the requirements of Health and Safety at Work etc Act 1974 and the Management of Health and Safety at Work Regulations 1999. Specifically, these are safety policies and risk assessments covering workplace related health and safety risks (HSE, 2006:7). In relation to COMAH’s regulatory function, COSHH or the UK Control of Substances Hazardous to Health Regulations imposes duties on employers to protect their employees from hazardous substances by limiting exposure to safe levels. For instance, COSHH requires that exposure reduction way below the MEL or the Maximum Exposure Limit for substances that can cause serious health effects such as cancer and occupational asthma. Another limitation imposes by COSHH is based on OES or the Occupational Exposure Standards which at a level at which based on scientific knowledge has no effect on the health of workers who are exposed and breath substance day after day (Chaiear, 2001:10). COSHH Regulations 2002 also regulates industry specific hazards such as offshore installations that are likely to generate H2S or Hydrogen sulphide which is heavier than air, toxic, and flammable. Through guiding COSHH help owners, operators, and contractors in carrying out risk assessments that can reduce workers exposure to toxic gases and other dangerous substances (HSE, 2011:1-3). Another relevant UK regulation is CHIP or the Chemical (Hazard Information and Packaging for Supply) Regulations 2009 (Smedley et al, 2013:2). CHIP applies to any dangerous substance that has the potential to harm people by contact with the skin and inhalation such as sulphuric acid, chlorine or hydrogen cyanide, benzene, carbon disulphide and other substances that can cause cancer, damage the kidney, liver, and lungs (Hawkins, 2002:135). The Factories Act 1961 demand compliance with highly flammable liquids and LPG regulations. For housing and community planning, the Housing and Planning Act 1986 regulates sites that may hold 25 tons or more of LPG while the Notifications of Installations Handling Hazardous Substances Regulations of 1982 requires consent of proper UK authorities and notify HSE for transport and handling of hazardous substances including compliance with provisions specified in Dangerous Substances (Conveyance by Road in Road Tankers and Tank Containers) Regulations 1981 and Road Traffic (Carriage of Dangerous Substances in Packages, etc.) Regulations 1986. In relation to these regulations, standards that must complied include BS 4250 for LPG, BS550 for unfired fusion welder pressure vessel, BS7122 for welded steel tanks for the road transport of liquefiable gas, BS 5355 for filling ratios and developed pressures for liquefiable and permanent gases, BS 5045 for transportable gas containers, and BS 4329 for non-refillable metallic containers up to 1.4 liters capacity for LPGs (Mobley 2001:333). 2.4 Toxic Gases Behaviour and Wind Effects Different types of toxic gases are produced, processed, stored, and transported thus any accident causing the escape of these gases can severely affect the environment and the people in the surrounding area. However, the extent of physiological effects of exposure to a toxic gas according to Tweedale (2003:132) depends on both the concentration and the duration of exposure. The concentration of toxic gases on an area away from the escape on the other hand depends on the weather at the time of the release, wind direction, wind speed, and the atmospheric activity. In other words, if gas consistently release from a single escape point and affected by the wind, it will move in the direction of the wind and disperse horizontally and vertically due to turbulence as shown below. Figure 1 - Plain view of gas plume as affected by wind (Tweedale, 2003) Note that this only illustrate a gas of almost similar density as that of air or a dense gas mixing with air as it travels downwind. Therefore, if the concentration of gas in remote area is to be calculated based on wind effects then gas release rate and wind speed are important variables as shown in Figure 2. Figure 2- Calculating gas concentration at a certain point using release rate and wind speed The illustrated gas behaviour above suggests that escaping gas from point X gradually disperse in both horizontal and vertical planes in the downwind direction. The area occupied by the plume on the other hand at given point is a function of the extent of both horizontal and vertical dispersion. Therefore, if the rate of release and wind speed is considered then the volume of air by which the gas is dispersed is equal to the horizontal dispersion, vertical dispersion, and wind speed. Similarly, the concentration on the area a given distance is equal to the rate of release divided by the volume into which the gas is mixed per second. Risk assessments for toxic gas releases often model dispersion using different wind conditions where the effect is measured by distances affected by hazardous gas clouds. According to Lines et al., (1996:1), distances reached by toxic gas clouds are often greater for low wind speeds (about 2ms-1). Similarly, dense gases behave differently when released into the atmosphere because it displaces the ambient atmospheric flow and modify ambient turbulent mixing. In other words, dense gases create heavy cold, liquid-laden clouds which in reality are heavier and can greatly affect the dispersion distance of a particular gas (Koopman et al.,1988:744). 2.5 Gas Release Modelling The release of gas and its subsequent behaviour is a significant event because as affected by the wind, gas concentration levels might affect people and communities. The mode of release and the behaviour of the gas according to Cameron & Raman (2005:243) are as important as the predicting the downwind gas concentrations because this will determine how gases will move towards wind direction and wind speed. Transient release for instance is momentary release of gas or puff (ex. safety devices relieving pressure) while continuous release (ex. broken pipe, split vessel, etc) may last longer and spread continuously downwind to longer distances. Another issue is the density of the released gas in relation to the surrounding air that can significantly affect concentrations such as dense gas dispersion (gases that initially roll to the ground and disperse as neutrally buoyant gases), positive buoyant dispersion (gas density lower than air), and neutrally buoyant dispersion (gas density similar to air). There are a number of models of gas release developed and most of them are about dispersion. For instance, the Gaussian models are used to determine the behaviour of neutrally buoyant gas released in the wind direction and wind speed. The neutral and positively buoyant plume and puff models are used to predict average concentration and time profiles of flammable or toxic materials downwind of a source. Basically, dispersion models are divided into two major groups. These include the neutrally buoyant models based on the Pasquill-Gifford model and the dense gas models based on box or top-hat representations. In the first group of models, positive buoyancy is assumed to occur whenever the gas released is above atmospheric temperature or with weight below that of air such as hydrogen, methane, and other hot stack gases that can act in a positively buoyant manner. CFD or computational fluid dynamics is often used to predict gas behaviour of dense gases. This group requires much more complex modelling such as DEGADIS, HGSYSTEM, PHAST, and others because heavier gases tend to undergo several flow regimes such as gravity spreading (horizontal), vertical movement, and transition to neutrally buoyant conditions as shown below (Cameron & Raman, 2005:243). Figure 3 -Typical heavy gas release and spread (Cameron & Raman, 2005:243) CFD Models for dispersion of lighter gas include ARIA local, a model that can calculate real-time dispersion of gases particularly with the urban environments, MISKAM or Microscale Flow and Dispersion Model that incorporate the effects of buildings and landscaping in gas dispersion, MICRO-CALGRID or Microscale California Photochemical Grid Model that uses flow fields and turbulence, and ATMoS or Atmospheric Transport Modelling System Dispersion Model developed for sulphur pollution (Gurjar et al, 2010:64). In real-life application, gas dispersion calculations should not only consider the density, wind direction, wind speed, and release rate but the complex topographical environment (Rigas & Amyotte, 2012:82). In other words, the solid obstacles in the dispersion area should be included in the computations particularly when mixing or interaction between gas and air and effects of turbulence in gas flow and direction is concern. CFD models according to Rigas & Amyotte (2012:82) are very useful in performing complex terrain dispersion simulation as numerical simulations is more realistic that experimental data particularly in consequence assessment of toxic gases dispersion scenarios in real terrain where other models are limited. In terms of wind effects, results obtained from CFD modelling according to Pasman & Kirilov (2008:382) seems more accurate because the wind velocity is completely resolved rather than being considered as a single value or mere function of height. For instance, obstacles such as buildings influence the flow and dispersion of gases because the residence time of toxic gases will be higher due to wake and cavities, turbulence is increased while gas spread faster in the crosswind direction. In complex geometry situations such as off-shore and on-shore facilities, CFD can be use to improve flow-field predictions and determine the volume filled by flammable gas cloud (Cameron & Raman, 2005:251). CFD identify other features of gas flow that cannot be predicted by simple modes particularly the near source effects (upwind spreading and overall cloud width) that are dependent on source size and momentum. It also shows the effect of wind direction in relation to release rate and wind speeds (IChemE, 1998:493). 2.6 Summary Toxic gas release is hazardous to health thus a number of regulations have been placed to ensure the safety of people within and around the vicinity of the incident. The effect of toxic gases is determined by the distance travelled and the amount of gas concentration in the remote area away from the source. Gas behaviour is dependent on the density of the gas, release rate, speed of air-gas mixing, wind direction, wind speed, turbulence as affected by obstacles and weather condition at the time of the event. Gas release rate, wind direction, and wind speed plays an important role in toxic gases dispersion. Wind effect is often determined by the type of gas being released thus equal and lighter than air and gases are easily affected by the wind while denser or heavier than air gases undergo several flow regimes such gravity horizontal spread before they can be fully affected by the wind as a neutrally buoyant gas. Gas release models are often focusing on dispersion and the density of gas being released. The Gaussian models are commonly use for positive and neutrally buoyant dispersion while CFD and other complex models are used for dense gases that often behave differently. CFD according to literature reviewed is more realistic compared to other models as it consider the effects of obstacles, wind direction, wind speed, turbulence, and factors that can affect gas behaviour. 3. Research Methodology 3.1 Introduction 3.2 Methodology 3.3 Data 3.4 Analysis and Discussion 3.5 Summary 4. Conclusions and Recommendations 4.1 Introduction 4.2 Conclusion and Recommendations 4.3 Recommendations for Further Research References Cameron I. & Raman R, (2005), Process Systems Risk Management, Academic Press, US CCPS, (2010), Guidelines for Consequence Analysis of Chemical Releases, John Wiley & Sons, US Chaiear N, (2001), Health and Safety in the Rubber Industry, iSmithers Rapra Publishing, US Fthenakis V, (1993), Prevention and Control of Accidental Releases of Hazardous Gases, John Wiley & Sons, US Gurjar B, Molina L, & Ojha C, (2010), Air Pollution: Health and Environmental Impacts, CRC Press, US Havenaar J, Cwikel, J, & Bromet E, (2002), Toxic Turmoil: Psychological and Societal Consequences of Ecological Disasters, Springer, Germany Hawkins L, (2002), Guide to Managing Employee Health, Taylor & Francis, UK HSE, (2006), A guide to the Control of Major Accident Hazards Regulations 1999 (as amended), Health and Safety Executive, UK HSE, (2011), OCE 6: Offshore COSHH essentials- Hydrogen sulphide, Health and Safety Executive, UK IChemE, (1998), Hazards XIV: Cost Effective Safety, Institution of Chemical Engineers, UK Maquire R, (2012), Safety Cases and Safety Reports: Meaning Motivation and Management, Ashgate Publishing, US Mobley R, (2001), Plant Engineer’s Handbook, Butterworth-Heinemann, UK Murphy B. & Morrison R, (2007), Introduction to Environmental Forensics, Academic Press, US National Fire Protection Association, (2008), Fundamentals of Fire Fighter Skills, Jones & Bartlett Learning, UK Pasman H. & Kirilov I, (2008), Resilience of Cities Terrorist and Other Threats, Springer, Germany Rigas F. & Amyotte P, (2012), Hydrogen Safety, CRC Press, US Smedley J, Dick F, & Sadhra S, (2013), Oxford Handbook of Occupational Health, Oxford University Press, UK Sutton I, (2010), Process Risk and Reliability Management: Operational Integrity Management, William Andrew Publishing, UK Trainor M, MacBeth R, & Balmforth H, (2004), Substance Prioritisation for the Development of EU Acute Exposure Toxicity Thresholds: Risk Informed Decision Making, Queen’s Printer, Scotland Tweedale M, (2003), Managing Risk and Reliability of Process Plants, Gulf Professional Publishing, UK Twoli N. & Mungai D, (2004), School Certificate Chemistry Form 3, East African Publishers, Nairobi Veasey D, McCormick L, & Hilyer B, (2005), Confined Space Entry and Emergency Response, John Wiley & Sons, US Bibliography Appendices Read More