Important to understand the meaning and relevance of specific terms when discussing hazards inherent in the oil and gas industry: flash point; vapour
Hazards Inherent in Oil and Gas
It is important to understand the meaning and relevance of specific terms when discussing hazards inherent in the oil and gas industry: flash point; vapour density and pressure; flammability and flammable limits; toxicity; skin irritant; and carcinogenic properties.The properties and hazards associated with different gases, particularly those relating to hydrogen, methane, liquefied petroleum gas (LPG), liquefied natural gas (LNG), nitrogen, hydrogen sulphide, and oxygen, are essential knowledge for those working in the industry.
Associated products (anti-foam and anti-wetting agents; micro-biocides; corrosion treatments; refrigerants; water and steam) have their own properties, hazards and control measures.
- Flash point – the lowest temperature at which there is sufficient vaporisation of a substance capable of producing a flash momentarily when a source of ignition is applied.
- Vapour density (mass of vapour per unit volume) or relative vapour density (density of the vapour relative to air) indicates whether a flammable vapour is likely to rise in the air, or, more commonly, sink and accumulate in low-lying areas
- Vapour pressure – the pressure exerted by a vapour when the liquid and vapour are in equilibrium (such as in a closed vessel).
- It increases with temperature and a high vapour pressure at a given temperature means that the liquid is very volatile and more likely to produce a flammable vapour.
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Flammable limits (also known as explosive limits when applied to explosions):
Lower flammable limit (LFL) or lower explosive limit (LEL): the minimum concentration of fuel in air that is sufficient to allow combustion to occur. Below the LFL, the mixture is too lean to burn.
Upper flammable limit (UFL) or upper explosive limit (UEL): the maximum concentration of fuel in air that is sufficient to allow combustion to occur. Above the UFL the mixture is too rich to burn
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Flammable, highly flammable and extremely flammable:
– Flammable liquid – liquids with a flash point 21-55°C (inclusive) (i.e. around ambient temperature).
– Highly flammable – liquids with a flash point less than 21°C (i.e. below ambient temperature), but which are not extremely flammable and certain reactive substances.
– Extremely flammable – liquids with a flash point below 0°C and a boiling point less than or equal to 35°C (i.e. very low flash point and low boiling point, therefore high volatility).
The upper and lower flammable limits are expressed in units of volume per cent. Between these limits is the flammable (or explosive) range. Gas detectors are used to control the hazard of fires and explosions and are set at a level below the lower explosive limit (LEL) to ensure that a flammable mixture does not exist anywhere in the area being monitored by the sensor (normally at, or under 10% of the LEL). - Acute toxicity - small doses cause death or serious ill health when ingested, inhaled or absorbed through the skin (e.g. potassium cyanide).
- Skin corrosion/irritation - destroys living skin tissue on contact or causes skin inflammation on contact.
- Serious eye damage/eye irritation - destroys eye tissue on contact or causes temporary inflammation of the eye.
- Respiratory or skin sensitisation - may cause sensitisation of the respiratory system or the skin through repeated or prolonged contact.
- Germ cell mutagenicity - may cause genetic damage that can be passed down to the next generation.
- Carcinogenicity - may cause cancer (abnormal and uncontrolled growth of cells in the body).
- Reproductive toxicity - may cause sterility or birth defects to an unborn child.
- Specific target organ toxicity (single and repeat exposure) - causes damage to body organs as a result of one single, large over-exposure or multiple exposures.
- Aspiration hazard - may cause damage to the respiratory system if accidentally inhaled into the lungs
Gases are used and created in the production and processing of oil and gas, so we must look at the properties of gases and the hazards associated with them
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- Hydrogen – widely used in petroleum refining as a catalyst regenerator, it is a highly flammable and explosive gas, which forms ignitable mixtures in air over a very wide range of concentrations (between 4.9% and 75%). It is colourless and odourless and very light, and explosive mixtures form rapidly. It can be easily ignited by low-energy sparks. It is not a toxic gas, but can asphyxiate at high concentrations. It can react vigorously with oxidising agents.
- Methane – also known as marsh gas and fire damp, it is used in the manufacture of hydrocarbons and is the main fuel constituent of natural gas. It is highly flammable and explosive, and forms an ignitable mixture with air over a wide range of concentrations (5% – 15%). Again, it is very light and may collect beneath structures such as roofs, ceilings and platforms, creating pockets of explosive mixtures. Methane is a simple asphyxiant, and an odorising agent is usually added to it.
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Liquefied Petroleum Gas (LPG) (Propane/Butane) – gas at normal temperature and pressure, but readily liquefied under pressure. It is a feedstock for chemical petroleum manufacture, as well as a fuel gas for heating, cooking, lighting, and the operation of internal combustion engines. It is also used as a fuel gas in welding and cutting, and in the manufacture of high-octane liquid fuels. LPG is highly flammable and, being denser than air, it collects at low level and readily forms an explosive mixture. In some cases, weak concentrations can be ignited with the flame readily flashing back to the source of a leak. Inhalation can lead to drowsiness, and exposure to moderately high concentrations can prove serious. It is colourless and odourless, and has an odorising agent added except where used in a chemical reaction. It is an asphyxiant.
The dangers of LPG lie with its flammability and explosive properties, and the fact that it is stored under great pressure, and hence very low temperatures, to retain its liquid state. On release, LPG reverts to its gaseous state, with rapid and considerable increase in volume.
While the main risks are from fire and explosion, the fact that the gas is heavier than air is of significance to persons working in low-lying or confined areas (such as excavations, pits, etc.) because of its asphyxiating properties. For persons handling cylinders, pipework and connections for LPG systems there is a risk of frost burns due to the low temperatures, and cylinders pose a manual-handling risk. Hazards Inherent in Oil and Gas - Liquefied Natural Gas (LNG) – as the name suggests, a liquefied methane (North Sea gas has 93.7% methane) used as a fuel gas for heating, cooking, etc. From the liquefied state it easily vaporises, forming a highly-flammable odourless gas, again having an odorising agent added. It will form an explosive mixture with air. Vapour can be ignited some distance away from a leak and the flame will spread back to the source. It is a simple asphyxiant, and non-toxic as a gas. Contact with its liquefied form will cause frostbite; LNG is cold (boiling at -161°C). On release, LNG reverts to its gaseous state, with rapid and considerable increase in volume. It is usually stored as a liquid at atmospheric pressure in special steel inner tanks with outer concrete shells with no bottom connections. Pressurised storage and transport is not used, reducing the dangers of catastrophic vessel failure with results such as boiling liquid expanding vapour explosions (BLEVEs). The unintentional release of LNG and its dispersion will create fire and explosion hazards such as pool fire spread, evaporation and pool fires.
- Nitrogen – a common odourless, colourless gas, tasteless and non-flammable, making up naturally 78% of the Earth’s atmosphere. Industrial nitrogen is produced by the fractional distillation of air. In industry it is commonly used to “inert” flammable atmospheres, as a “cover” on flammable and explosive substances (a gas layer lying above the liquid in a tank) and to inflate tyres, used in a form often called OFN – oxygen-free nitrogen. In addition to inerting and cover capabilities, liquefied nitrogen is used for pipe freezing and pipeline purging. Offshore it is used for a number of well services operations, such as drill stem testing or perforating operations, nitrogen lift, etc.
- Hydrogen Sulphide – a colourless flammable gas with an offensive odour of rotten eggs, which forms explosive mixtures with air over a wide range of concentrations (4% – 46%). It is denser than air and will accumulate in low-level areas, and can travel long distances to an ignition source and flash back. Hydrogen sulphide is toxic, and will irritate the eyes, skin and respiratory tract and can lead to respiratory paralysis. It will rapidly deaden the sense of smell, so its odour cannot be relied on to detect it. It often occurs in natural areas, such as swamps, ponds and lagoons and where there is rotting vegetable matter. The effects of hydrogen sulphide depend on duration of exposure, frequency of exposure and the intensity (concentration of the gas), as well as the susceptibility of the person exposed Since it is present in some subsurface formations, drilling and other operational crews must be prepared to use detection equipment, personal protective equipment (particularly respiratory protective equipment) and require adequate training backed up by contingency procedures in case of overexposure in hydrogen sulphide-prone areas. It will enter drilling mud from subsurface formations, can be generated by sulphate-reducing bacteria in stored muds, and formed in concrete leg platforms below the gas-tight floor
- Oxygen – a colourless, odourless gas that is essential to support combustion. Oxygen enrichment can lead to fires and explosion, and will react violently with oils and greases. It is used with fuel gases in welding and burning to intensify combustion. Oxygen is non-flammable, but will encourage combustion, combustible materials becoming more easily ignited in an oxygen-enriched atmosphere. They burn far more rapidly with near explosive violence, as illustrated by the fire that broke out on HMS Glasgow, Newcastle upon Tyne, UK, below decks in an atmosphere enriched by leaking oxygen cylinders. The fierce, rapid fire caused the death of eight workers on the ship and others, including fire-fighters, were overcome by smoke and needed hospital treatment. Oxygen can easily be absorbed into clothing and under these conditions a simple spark or other small source of ignition can result in flash-burning. Oxygen is sometimes used offshore to detect and quantify the flow of water in or around a borehole based on oxygen activation.
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- 1. Inherent and Residual Risk With Risk Appetite
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- 2. Assessing Inherent Risk
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- 3. Inherent Safety at Chemical Sites
- 4. Inherent Safety in Process Plant Design
- 1. Inherent and Residual Risk With Risk Appetite
- 2. Assessing Inherent Risk
- 3. Inherent Safety at Chemical Sites
- 4. Inherent Safety in Process Plant Design