The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium; the melting point of a substance depends on pressure and is specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point; because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point. For most substances and freezing points are equal. For example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures.
For example, agar melts at 85 °C and solidifies from 31 °C. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances, the freezing point of water is not always the same as the melting point. In the absence of nucleators water can exist as a supercooled liquid down to −48.3 °C before freezing. The chemical element with the highest melting point is tungsten, at 3,414 °C; the often-cited carbon does not melt at ambient pressure but sublimes at about 3,726.85 °C. Tantalum hafnium carbide is a refractory compound with a high melting point of 4215 K. At the other end of the scale, helium does not freeze at all at normal pressure at temperatures arbitrarily close to absolute zero. Many laboratory techniques exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip, revealing its thermal behaviour at the temperature at that point. Differential scanning calorimetry gives information on melting point together with its enthalpy of fusion.
A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window and a simple magnifier. The several grains of a solid are placed in a thin glass tube and immersed in the oil bath; the oil bath is heated and with the aid of the magnifier melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, optical detection is automated; the measurement can be made continuously with an operating process. For instance, oil refineries measure the freeze point of diesel fuel online, meaning that the sample is taken from the process and measured automatically; this allows for more frequent measurements as the sample does not have to be manually collected and taken to a remote laboratory. For refractory materials the high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees.
The spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source, calibrated as a function of temperature. In this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer. For temperatures above the calibration range of the source, an extrapolation technique must be employed; this extrapolation is accomplished by using Planck's law of radiation. The constants in this equation are not known with sufficient accuracy, causing errors in the extrapolation to become larger at higher temperatures. However, standard techniques have been developed to perform this extrapolation. Consider the case of using gold as the source. In this technique, the current through the filament of the pyrometer is adjusted until the light intensity of the filament matches that of a black-body at the melting point of gold.
This establishes the primary calibration temperature and can be expressed in terms of current through the pyrometer lamp. With the same current setting, the pyrometer is sighted on another black-body at a higher temperature. An absorbing medium of known transmission is inserted between this black-body; the temperature of the black-body is adjusted until a match exists between its intensity and that of the pyrometer filament. The true higher temperature of the black-body is determined from Planck's Law; the absorbing medium is removed and the current through the filament is adjusted to match the filament intensity to that of the black-body. This establishes a second calibration point for the pyrometer; this step is repeated to carry the calibration to hi
Ethers are a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R -- O -- R ′, where R ′ represent the alkyl or aryl groups. Ethers can again be classified into two varieties: if the alkyl groups are the same on both sides of the oxygen atom it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anesthetic diethyl ether referred to as "ether". Ethers are common in organic chemistry and more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin. Ethers feature C–O–C linkage defined by a bond angle of about 110° and C–O distances of about 140 pm; the barrier to rotation about the C–O bonds is low. The bonding of oxygen in ethers and water is similar. In the language of valence bond theory, the hybridization at oxygen is sp3. Oxygen is more electronegative than carbon, thus the hydrogens alpha to ethers are more acidic than in simple hydrocarbons.
They are far less acidic than hydrogens alpha to carbonyl groups, however. Depending on the groups at R and R′, ethers are classified into two types:Simple ethers or symmetrical ethers. Mixed ethers or asymmetrical ethers. In the IUPAC nomenclature system, ethers are named using the general formula "alkoxyalkane", for example CH3–CH2–O–CH3 is methoxyethane. If the ether is part of a more-complex molecule, it is described as an alkoxy substituent, so –OCH3 would be considered a "methoxy-" group; the simpler alkyl radical is written in front, so CH3–O–CH2CH3 would be given as methoxyethane. IUPAC rules are not followed for simple ethers; the trivial names for simple ethers are a composite of the two substituents followed by "ether". For example, ethyl methyl ether, diphenylether; as for other organic compounds common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is called "ether", but was once called sweet oil of vitriol. Methyl phenyl ether is anisole, because it was found in aniseed.
The aromatic ethers include furans. Acetals are another class of ethers with characteristic properties. Polyethers are compounds with more than one ether group; the crown ethers are examples of small polyethers. Some toxins produced by dinoflagellates such as brevetoxin and ciguatoxin are large and are known as cyclic or ladder polyethers. Polyether refers to polymers which contain the ether functional group in their main chain; the term glycol is reserved for low to medium range molar mass polymer when the nature of the end-group, a hydroxyl group, still matters. The term "oxide" or other terms are used for high molar mass polymer when end-groups no longer affect polymer properties; the phenyl ether polymers are a class of aromatic polyethers containing aromatic cycles in their main chain: Polyphenyl ether and Poly. Many classes of compounds with C–O–C linkages are not considered ethers: Esters, carboxylic acid anhydrides. Ether molecules cannot form hydrogen bonds with each other, resulting in low boiling points compared to those of the analogous alcohols.
The difference in the boiling points of the ethers and their isomeric alcohols becomes lower as the carbon chains become longer, as the van der Waals interactions of the extended carbon chain dominates over the presence of hydrogen bonding. Ethers are polar; the C–O–C bond angle in the functional group is about 110°, the C–O dipoles do not cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters, or amides of comparable structure; the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible. Cyclic ethers such as tetrahydrofuran and 1,4-dioxane are miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to linear aliphatic ethers. Other properties are: The lower ethers are volatile and flammable. Lower ethers act as anaesthetics. Ethers are good organic solvents. Simple ethers are tasteless. Ethers are quite stable chemical compounds which do not react with bases, active metals, dilute acids, oxidising agents, reducing agents.
They are of low chemical reactivity, but they are more reactive than alkanes. Epoxides and acetals are unrepresentative classes of ethers and are discussed in separate articles. Important reactions are listed below. Although ethers resist hydrolysis, their polar bonds are cloven by mineral acids such as hydrobromic acid and hydroiodic acid. Hydrogen chloride cleaves ethers only slowly. Methyl ethers afford methyl halides: ROCH3 + HBr → CH3Br + ROHThese reactions proceed via onium intermediates, i.e. +Br−. Some ethers undergo rapid cleavage with boron tribromide to give the alkyl bromide. Depending on the substituents, some ethers can be cloven with a variety of reagents, e.g. strong base. When stored in the presence of air or oxygen, ethers tend to form explosive peroxides, such as diethyl ether peroxide; the reaction is accelerated by light, metal catalysts, aldehydes. In addition to avoiding storage conditions to form peroxides, it is recommended, when an ether is used as a solvent, not to distill it to dryness, as any peroxides that may have formed, being less volatil
Benzene is an organic chemical compound with the chemical formula C6H6. The benzene molecule is composed of six carbon atoms joined in a ring with one hydrogen atom attached to each; as it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is one of the elementary petrochemicals. Due to the cyclic continuous pi bond between the carbon atoms, benzene is classed as an aromatic hydrocarbon, the second -annulene, it is sometimes abbreviated PhH. Benzene is a colorless and flammable liquid with a sweet smell, is responsible for the aroma around petrol stations, it is used as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. As benzene has a high octane number, aromatic derivatives like toluene and xylene comprise up to 25% of gasoline. Benzene itself has been limited to less than 1 % in gasoline. Most non-industrial applications have been limited as well for the same reason.
The word "benzene" derives from "gum benzoin", an aromatic resin known to European pharmacists and perfumers since the 15th century as a product of southeast Asia. An acidic material was derived from benzoin by sublimation, named "flowers of benzoin", or benzoic acid; the hydrocarbon derived from benzoic acid thus acquired benzol, or benzene. Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen. In 1833, Eilhard Mitscherlich produced it by distilling benzoic lime, he gave the compound the name benzin. In 1836, the French chemist Auguste Laurent named the substance "phène". In 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. Four years Mansfield began the first industrial-scale production of benzene, based on the coal-tar method; the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family.
In 1855, Hofmann used the word "aromatic" to designate this family relationship, after a characteristic property of many of its members. In 1997, benzene was detected in deep space; the empirical formula for benzene was long known, but its polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper in 1858 and Joseph Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but too little evidence was available to help chemists decide on any particular structure. In 1865, the German chemist Friedrich August Kekulé published a paper in French suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds; the next year he published a much longer paper in German on the same subject. Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, that there always appeared to be three isomers of every disubstituted derivative—now understood to correspond to the ortho and para patterns of arene substitution—to argue in support of his proposed structure.
Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio. The new understanding of benzene, hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory, he said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail. This vision, came to him after years of studying the nature of carbon-carbon bonds; this was 7 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled Berichte der Durstigen Chemischen Gesellschaft, a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote.
Some historians have suggested that the parody was a lampoon of the snake anecdote already well known through oral transmission if it had not yet appeared in print. Kekulé's 1890 speech in which this anecdote appeared has been translated into English. If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862; the cyclic nature of benzene was confirmed by the crystallographer Kathleen Lonsdale in 1929. The German chemist Wilhelm Körner suggested the prefixes ortho-, meta-, para- to distinguish di-substituted benzene derivatives in 1867, it was the German chemist Karl Gräbe who, in 1869, first used the prefixes ortho-, meta-, para- to denote specific relative locations of the substituents on a di-substituted aromatic ring (viz, nap
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water at 93.4 °C at 1,905 metres altitude. For a given pressure, different liquids will boil at different temperatures; the normal boiling point of a liquid is the special case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid; the standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of 1 bar.
The heat of vaporization is the energy required to transform a given quantity of a substance from a liquid into a gas at a given pressure. Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. Evaporation is a surface phenomenon in which molecules located near the liquid's edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid. A saturated liquid contains as much thermal energy. Saturation temperature means boiling point; the saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition. If the pressure in a system remains constant, a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy is removed.
A liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied. The boiling point corresponds to the temperature at which the vapor pressure of the liquid equals the surrounding environmental pressure. Thus, the boiling point is dependent on the pressure. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa, or the IUPAC standard pressure of 100.000 kPa. At higher elevations, where the atmospheric pressure is much lower, the boiling point is lower; the boiling point increases with increased pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point; the boiling point decreases with decreasing pressure until the triple point is reached. The boiling point cannot be reduced below the triple point. If the heat of vaporization and the vapor pressure of a liquid at a certain temperature are known, the boiling point can be calculated by using the Clausius–Clapeyron equation, thus: T B = − 1, where: T B is the boiling point at the pressure of interest, R is the ideal gas constant, P is the vapour pressure of the liquid at the pressure of interest, P 0 is some pressure where the corresponding T 0 is known, Δ H vap is the heat of vaporization of the liquid, T 0 is the boiling temperature, ln is the natural logarithm.
Saturation pressure is the pressure for a corresponding saturation temperature at which a liquid boils into its vapor phase. Saturation pressure and saturation temperature have a direct relationship: as saturation pressure is increased, so is saturation temperature. If the temperature in a system remains constant, vapor at saturation pressure and temperature will begin to condense into its liquid phase as the system pressure is increased. A liquid at saturation pressure and temperature will tend to flash into its vapor phase as system pressure is decreased. There are two conventions regarding the standard boiling point of water: The normal boiling point is 99.97 °C at a pressure of 1 atm. The IUPAC recommended standard boiling point of water at a standard pressure of 100 kPa is 99.61 °C. For comparison, on top of Mount Everest, at 8,848 m elevation, the pressure is about 34 kPa and the boiling point of water is 71 °C; the Celsius temperature scale was defined until 1954 by two points: 0 °C being defined by the wate
Gasoline, gas or petrol is a colorless petroleum-derived flammable liquid, used as a fuel in spark-ignited internal combustion engines. It consists of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. On average, a 42-U. S.-gallon barrel of crude oil yields about 19 U. S. gallons of gasoline after processing in an oil refinery, though this varies based on the crude oil assay. The characteristic of a particular gasoline blend to resist igniting too early is measured by its octane rating. Gasoline is produced in several grades of octane rating. Tetraethyl lead and other lead compounds are no longer used in most areas to increase octane rating. Other chemicals are added to gasoline to improve chemical stability and performance characteristics, control corrosiveness and provide fuel system cleaning. Gasoline may contain oxygen-containing chemicals such as ethanol, MTBE or ETBE to improve combustion. Gasoline used in internal combustion engines can have significant effects on the local environment, is a contributor to global human carbon dioxide emissions.
Gasoline can enter the environment uncombusted, both as liquid and as vapor, from leakage and handling during production and delivery. As an example of efforts to control such leakage, many underground storage tanks are required to have extensive measures in place to detect and prevent such leaks. Gasoline contains other known carcinogens. "Gasoline" is a North American word. The Oxford English Dictionary dates its first recorded use to 1863 when it was spelled "gasolene"; the term "gasoline" was first used in North America in 1864. The word is a derivation from the word "gas" and the chemical suffixes "-ol" and "-ine" or "-ene". However, the term may have been influenced by the trademark "Cazeline" or "Gazeline". On 27 November 1862, the British publisher, coffee merchant and social campaigner John Cassell placed an advertisement in The Times of London: The Patent Cazeline Oil, safe and brilliant … possesses all the requisites which have so long been desired as a means of powerful artificial light.
This is the earliest occurrence of the word to have been found. Cassell discovered that a shopkeeper in Dublin named Samuel Boyd was selling counterfeit cazeline and wrote to him to ask him to stop. Boyd did not reply and changed every ‘C’ into a ‘G’, thus coining the word "gazeline"; the name "petrol" is used in place of "gasoline" in most Commonwealth countries. "Petrol" was first used as the name of a refined petroleum product around 1870 by British wholesaler Carless, Capel & Leonard, who marketed it as a solvent. When the product found a new use as a motor fuel, Frederick Simms, an associate of Gottlieb Daimler, suggested to Carless that they register the trademark "petrol", but by this time the word was in general use inspired by the French pétrole, the registration was not allowed. Carless registered a number of alternative names for the product, but "petrol" nonetheless became the common term for the fuel in the British Commonwealth. British refiners used "motor spirit" as a generic name for the automotive fuel and "aviation spirit" for aviation gasoline.
When Carless was denied a trademark on "petrol" in the 1930s, its competitors switched to the more popular name "petrol". However, "motor spirit" had made its way into laws and regulations, so the term remains in use as a formal name for petrol; the term is used most in Nigeria, where the largest petroleum companies call their product "premium motor spirit". Although "petrol" has made inroads into Nigerian English, "premium motor spirit" remains the formal name, used in scientific publications, government reports, newspapers; the use of the word gasoline instead of petrol outside North America can be confusing. Shortening gasoline to gas, which happens causes confusion with various forms of gaseous products used as automotive fuel like compressed natural gas, liquefied natural gas and liquefied petroleum gas ). In many languages, the name is derived from benzene, such as Benzin in benzina in Italian. Argentina and Paraguay use the colloquial name nafta derived from that of the chemical naphtha.
The first internal combustion engines suitable for use in transportation applications, so-called Otto engines, were developed in Germany during the last quarter of the 19th century. The fuel for these early engines was a volatile hydrocarbon obtained from coal gas. With a boiling point near 85 °C, it was well-suited for early carburetors; the development of a "spray nozzle" carburetor enabled the use of less volatile fuels. Further improvements in engine efficiency were attempted at higher compression ratios, but early attempts were blocked by the premature explosion of fuel, known as knocking. In 1891, the Shukhov cracking process became the world's first commercial method to break down heavier hydrocarbons in crude oil to increase the percentage of lighter products compared to simple distillation; the evolution of gasoline followed the evolution of oil as the dominant source of energy in the industrializing world. Prior to World War One, Britain was the world's greatest industrial power and depended on its navy to protect the shipping of raw materials from its colonies.
Germany was industrializing and, like Britain, lacked many natural resources which had to be shipped to the home country. By the 1890s, Germany
Solubility is the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature and presence of other chemicals of the solution; the extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute. Insolubility is the inability to dissolve in a liquid or gaseous solvent. Most the solvent is a liquid, which can be a pure substance or a mixture. One may speak of solid solution, but of solution in a gas. Under certain conditions, the equilibrium solubility can be exceeded to give a so-called supersaturated solution, metastable. Metastability of crystals can lead to apparent differences in the amount of a chemical that dissolves depending on its crystalline form or particle size.
A supersaturated solution crystallises when'seed' crystals are introduced and rapid equilibration occurs. Phenylsalicylate is one such simple observable substance when melted and cooled below its fusion point. Solubility is not to be confused with the ability to'dissolve' a substance, because the solution might occur because of a chemical reaction. For example, zinc'dissolves' in hydrochloric acid as a result of a chemical reaction releasing hydrogen gas in a displacement reaction; the zinc ions are soluble in the acid. The solubility of a substance is an different property from the rate of solution, how fast it dissolves; the smaller a particle is, the faster it dissolves although there are many factors to add to this generalization. Crucially solubility applies to all areas of chemistry, inorganic, physical and biochemistry. In all cases it will depend on the physical conditions and the enthalpy and entropy directly relating to the solvents and solutes concerned. By far the most common solvent in chemistry is water, a solvent for most ionic compounds as well as a wide range of organic substances.
This is a crucial factor in much environmental and geochemical work. According to the IUPAC definition, solubility is the analytical composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in various units of concentration such as molarity, mole fraction, mole ratio, mass per volume and other units; the extent of solubility ranges from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is applied to poorly or poorly soluble compounds. A number of other descriptive terms are used to qualify the extent of solubility for a given application. For example, U. S. Pharmacopoeia gives the following terms: The thresholds to describe something as insoluble, or similar terms, may depend on the application. For example, one source states that substances are described as "insoluble" when their solubility is less than 0.1 g per 100 mL of solvent. Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution and phase joining.
The solubility equilibrium occurs. The term solubility is used in some fields where the solute is altered by solvolysis. For example, many metals and their oxides are said to be "soluble in hydrochloric acid", although in fact the aqueous acid irreversibly degrades the solid to give soluble products, it is true that most ionic solids are dissolved by polar solvents, but such processes are reversible. In those cases where the solute is not recovered upon evaporation of the solvent, the process is referred to as solvolysis; the thermodynamic concept of solubility does not apply straightforwardly to solvolysis. When a solute dissolves, it may form several species in the solution. For example, an aqueous suspension of ferrous hydroxide, Fe2, will contain the series + as well as other species. Furthermore, the solubility of ferrous hydroxide and the composition of its soluble components depend on pH. In general, solubility in the solvent phase can be given only for a specific solute, thermodynamically stable, the value of the solubility will include all the species in the solution.
Solubility is defined for specific phases. For example, the solubility of aragonite and calcite in water are expected to differ though they are both polymorphs of calcium carbonate and have the same chemical formula; the solubility of one substance in another is determined by the balance of intermolecular forces between the solvent and solute, the entropy change that accompanies the solvation. Factors such as temperature and pressure will alter this balance. Solubility may strongly depend on the presence of other species dissolved in the solvent, for example, complex-forming anions in liquids. Solubility will depend on the excess or deficiency of a common ion in the solution, a phenomenon known as the common-ion effect. To a lesser extent, solubility will depend on the ionic strength of solutions; the last two effects can be quantified using the equation for solubility equilibrium. For a solid that dissolves in a redox reaction, solubility is expe
Occupational safety and health
Occupational safety and health commonly referred to as occupational health and safety, occupational health, or workplace health and safety, is a multidisciplinary field concerned with the safety and welfare of people at work. These terms refer to the goals of this field, so their use in the sense of this article was an abbreviation of occupational safety and health program/department etc; the goals of occupational safety and health programs include to foster a safe and healthy work environment. OSH may protect co-workers, family members, employers and many others who might be affected by the workplace environment. In the United States, the term occupational health and safety is referred to as occupational health and occupational and non-occupational safety and includes safety for activities outside of work. In common-law jurisdictions, employers have a common law duty to take reasonable care of the safety of their employees. Statute law may in addition impose other general duties, introduce specific duties, create government bodies with powers to regulate workplace safety issues: details of this vary from jurisdiction to jurisdiction.
As defined by the World Health Organization "occupational health deals with all aspects of health and safety in the workplace and has a strong focus on primary prevention of hazards." Health has been defined as "a state of complete physical and social well-being and not the absence of disease or infirmity." Occupational health is a multidisciplinary field of healthcare concerned with enabling an individual to undertake their occupation, in the way that causes least harm to their health. Health has been defined as It contrasts, for example, with the promotion of health and safety at work, concerned with preventing harm from any incidental hazards, arising in the workplace. Since 1950, the International Labour Organization and the World Health Organization have shared a common definition of occupational health, it was adopted by the Joint ILO/WHO Committee on Occupational Health at its first session in 1950 and revised at its twelfth session in 1995. The definition reads: "The main focus in occupational health is on three different objectives: the maintenance and promotion of workers’ health and working capacity.
The concept of working culture is intended in this context to mean a reflection of the essential value systems adopted by the undertaking concerned. Such a culture is reflected in practice in the managerial systems, personnel policy, principles for participation, training policies and quality management of the undertaking." Those in the field of occupational health come from a wide range of disciplines and professions including medicine, epidemiology and rehabilitation, occupational therapy, occupational medicine, human factors and ergonomics, many others. Professionals advise on a broad range of occupational health matters; these include how to avoid particular pre-existing conditions causing a problem in the occupation, correct posture for the work, frequency of rest breaks, preventative action that can be undertaken, so forth. "Occupational health should aim at: the promotion and maintenance of the highest degree of physical and social well-being of workers in all occupations. The research and regulation of occupational safety and health are a recent phenomenon.
As labor movements arose in response to worker concerns in the wake of the industrial revolution, worker's health entered consideration as a labor-related issue. In the United Kingdom, the Factory Acts of the early nineteenth century arose out of concerns about the poor health of children working in cotton mills: the Act of 1833 created a dedicated professional Factory Inspectorate; the initial remit of the Inspectorate was to police restrictions on the working hours in the textile industry of children and young persons. However, on the urging of the Factory Inspectorate, a further Act in 1844 giving similar restrictions on working hours for women in the textile industry introduced a requirement for machinery guarding. In 1840 a Royal Commission published its findings on the state of conditions for the workers of the mining industry that documented the appallingly dangerous environment that they had to work in and the high frequency of accidents; the commission sparked public outrage which resulted in the Mines Act of 1842.
The act set up an inspectorate for mines and collieries which resulted in many prosecutions and safety improvements, by 1850, inspectors were able to enter and inspect premises at their discretion. Otto von Bismarck inaugurated the first social insurance legislation in 1883 and the first worker's compensation law in 1884 – the first of their kind in the Western world. Similar acts followed in other countries