Phenol is an aromatic organic compound with the molecular formula C6H5OH. It is a white crystalline solid, volatile; the molecule consists of a phenyl group bonded to a hydroxy group. It requires careful handling due to its propensity for causing chemical burns. Phenol was first extracted from coal tar, it is an important industrial commodity as a precursor to useful compounds. It is used to synthesize plastics and related materials. Phenol and its chemical derivatives are essential for production of polycarbonates, Bakelite, detergents, herbicides such as phenoxy herbicides, numerous pharmaceutical drugs. Phenol is an organic compound appreciably soluble in water, with about 84.2 g dissolving in 1000 mL. Homogeneous mixtures of phenol and water at phenol to water mass ratios of ~2.6 and higher are possible. The sodium salt of phenol, sodium phenoxide, is far more water-soluble. Phenol is weakly acidic and at high pHs gives the phenolate anion C6H5O−: PhOH ⇌ PhO− + H+ Compared to aliphatic alcohols, phenol is about 1 million times more acidic, although it is still considered a weak acid.
It reacts with aqueous NaOH to lose H+, giving the salt sodium phenoxide, whereas most alcohols react only partially. One explanation for the increased acidity over alcohols is resonance stabilization of the phenoxide anion by the aromatic ring. In this way, the negative charge on oxygen is delocalized on to the ortho and para carbon atoms through the pi system. An alternative explanation involves the sigma framework, postulating that the dominant effect is the induction from the more electronegative sp2 hybridised carbons. In support of the second explanation, the pKa of the enol of acetone in water is 10.9, making it only less acidic than phenol. Thus, the greater number of resonance structures available to phenoxide compared to acetone enolate seems to contribute little to its stabilization. However, the situation changes. A recent in silico comparison of the gas phase acidities of the vinylogues of phenol and cyclohexanol in conformations that allow for or exclude resonance stabilization leads to the inference that about 1⁄3 of the increased acidity of phenol is attributable to inductive effects, with resonance accounting for the remaining difference.
The phenoxide anion has a similar nucleophilicity to free amines, with the further advantage that its conjugate acid does not become deactivated as a nucleophile in moderately acidic conditions. Phenolate esters are more stable toward hydrolysis than acid anhydrides and acyl halides but are sufficiently reactive under mild conditions to facilitate the formation of amide bonds. Phenol exhibits keto-enol tautomerism with its unstable keto tautomer cyclohexadienone, but only a tiny fraction of phenol exists as the keto form; the equilibrium constant for enolisation is 10−13, which means only one in every ten trillion molecules is in the keto form at any moment. The small amount of stabilisation gained by exchanging a C=C bond for a C=O bond is more than offset by the large destabilisation resulting from the loss of aromaticity. Phenol therefore exists entirely in the enol form. Phenoxides are enolates stabilised by aromaticity. Under normal circumstances, phenoxide is more reactive at the oxygen position, but the oxygen position is a "hard" nucleophile whereas the alpha-carbon positions tend to be "soft".
Phenol is reactive toward electrophilic aromatic substitution as the oxygen atom's pi electrons donate electron density into the ring. By this general approach, many groups can be appended to the ring, via halogenation, acylation and other processes. However, phenol's ring is so activated—second only to aniline—that bromination or chlorination of phenol leads to substitution on all carbon atoms ortho and para to the hydroxy group, not only on one carbon. Phenol reacts with dilute nitric acid at room temperature to give a mixture of 2-nitrophenol and 4-nitrophenol while with concentrated nitric acid, more nitro groups get substituted on the ring to give 2,4,6-trinitrophenol, known as picric acid. Aqueous solutions of phenol are weakly acidic and turn blue litmus to red. Phenol is neutralized by sodium hydroxide forming sodium phenate or phenolate, but being weaker than carbonic acid, it cannot be neutralized by sodium bicarbonate or sodium carbonate to liberate carbon dioxide. C6H5OH + NaOH → C6H5ONa + H2OWhen a mixture of phenol and benzoyl chloride are shaken in presence of dilute sodium hydroxide solution, phenyl benzoate is formed.
This is an example of the Schotten-Baumann reaction: C6H5OH + C6H5COCl → C6H5OCOC6H5 + HClPhenol is reduced to benzene when it is distilled with zinc dust, or when phenol vapour is passed over granules of zinc at 400 °C: C6H5OH + Zn → C6H6 + ZnOWhen phenol is reacted with diazomethane in the presence of boron trifluoride, anisole is obtained as the main product and nitrogen gas as a byproduct. C6H5OH + CH2N2 → C6H5OCH3 + N2When phenol reacts with iron chloride solution, an intense violet-purple solution is formed; because of phenol's commercial importance, many methods have been developed for its production. The dominant current route, accounting for 95% of production, is the cumene process, which uses benzene and propene as feedstock and involves the partial oxidation of cumene vi
European Chemicals Agency
The European Chemicals Agency is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation and Restriction of Chemicals. ECHA is the driving force among regulatory authorities in implementing the EU's chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and addresses chemicals of concern, it is located in Finland. The agency headed by Executive Director Bjorn Hansen, started working on 1 June 2007; the REACH Regulation requires companies to provide information on the hazards and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most used substances have been registered; the information is technical but gives detail on the impact of each chemical on people and the environment.
This gives European consumers the right to ask retailers whether the goods they buy contain dangerous substances. The Classification and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU; this worldwide system makes it easier for workers and consumers to know the effects of chemicals and how to use products safely because the labels on products are now the same throughout the world. Companies need to notify ECHA of the labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100 000 substances; the information is available on their website. Consumers can check chemicals in the products. Biocidal products include, for example, insect disinfectants used in hospitals; the Biocidal Products Regulation ensures that there is enough information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation; the law on Prior Informed Consent sets guidelines for the import of hazardous chemicals.
Through this mechanism, countries due to receive hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have serious effects on human health and the environment are identified as Substances of Very High Concern 1; these are substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment and do not break down. Other substances considered. Companies manufacturing or importing articles containing these substances in a concentration above 0,1% weight of the article, have legal obligations, they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy. Once a substance has been identified in the EU as being of high concern, it will be added to a list; this list is available on ECHA's website and shows consumers and industry which chemicals are identified as SVHCs.
Substances placed on the Candidate List can move to another list. This means that, after a given date, companies will not be allowed to place the substance on the market or to use it, unless they have been given prior authorisation to do so by ECHA. One of the main aims of this listing process is to phase out SVHCs where possible. In its 2018 substance evaluation progress report, ECHA said chemical companies failed to provide “important safety information” in nearly three quarters of cases checked that year. "The numbers show a similar picture to previous years" the report said. The agency noted that member states need to develop risk management measures to control unsafe commercial use of chemicals in 71% of the substances checked. Executive Director Bjorn Hansen called non-compliance with REACH a "worry". Industry group CEFIC acknowledged the problem; the European Environmental Bureau called for faster enforcement to minimise chemical exposure. European Chemicals Bureau Official website
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
Manganese oxide is the inorganic compound with the formula MnO2. This blackish or brown solid occurs as the mineral pyrolusite, the main ore of manganese and a component of manganese nodules; the principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the zinc-carbon battery. MnO2 is used as a pigment and as a precursor to other manganese compounds, such as KMnO4, it is used for example, for the oxidation of allylic alcohols. MnO2 in the α polymorph can incorporate a variety of atoms in the "tunnels" or "channels" between the manganese oxide octahedra. There is considerable interest in α-MnO2 as a possible cathode for lithium ion batteries. Several polymorphs of MnO2 are claimed, as well as a hydrated form. Like many other dioxides, MnO2 crystallizes in the rutile crystal structure, with three-coordinate oxide and octahedral metal centres. MnO2 is characteristically nonstoichiometric, being deficient in oxygen; the complicated solid-state chemistry of this material is relevant to the lore of "freshly prepared" MnO2 in organic synthesis.
The α-polymorph of MnO2 has a open structure with "channels" which can accommodate metal atoms such as silver or barium. Α-MnO2 is called hollandite, after a related mineral. Occurring manganese dioxide contains impurities and a considerable amount of manganese oxide. Only a limited number of deposits contain the γ modification in purity sufficient for the battery industry. Production of batteries and ferrite requires high purity manganese dioxide. Batteries require "electrolytic manganese dioxide" while ferrites require "chemical manganese dioxide". One method starts with natural manganese dioxide and converts it using dinitrogen tetroxide and water to a manganese nitrate solution. Evaporation of the water, leaves the crystalline nitrate salt. At temperatures of 400 °C, the salt decomposes, releasing N2O4 and leaving a residue of purified manganese dioxide; these two steps can be summarized as: MnO2 + N2O4 ⇌ Mn2In another process manganese dioxide is carbothermically reduced to manganese oxide, dissolved in sulfuric acid.
The filtered solution is treated with ammonium carbonate to precipitate MnCO3. The carbonate is calcined in air to give a mixture of manganese oxides. To complete the process, a suspension of this material in sulfuric acid is treated with sodium chlorate. Chloric acid, which forms in situ, converts any Mn and Mn oxides to the dioxide, releasing chlorine as a by-product. A third process involves manganese manganese monoxide; the two reagents combine with a 1:3 ratio to form manganese dioxide: Mn2O7 + 3 MnO → 5 MnO2Lastly the action of potassium permanganate over manganese sulphate crystals produces the desired oxide. 2 KMnO4 + 3 MnSO4 + 2 H2O→ 5 MnO2 + K2SO4 + 2 H2SO4 Electrolytic manganese dioxide is used in zinc–carbon batteries together with zinc chloride and ammonium chloride. EMD is used in zinc manganese dioxide rechargeable alkaline cells also. For these applications, purity is important. EMD is produced in a similar fashion as electrolytic tough pitch copper: The manganese dioxide is dissolved in sulfuric acid and subjected to a current between two electrodes.
The MnO2 dissolves, enters solution as the sulfate, is deposited on the anode. The important reactions of MnO2 are associated with both oxidation and reduction. MnO2 is the principal precursor to ferromanganese and related alloys, which are used in the steel industry; the conversions involve carbothermal reduction using coke: MnO2 + 2 C → Mn + 2 COThe key reactions of MnO2 in batteries is the one-electron reduction: MnO2 + e− + H+ → MnOMnO2 catalyses several reactions that form O2. In a classical laboratory demonstration, heating a mixture of potassium chlorate and manganese dioxide produces oxygen gas. Manganese dioxide catalyses the decomposition of hydrogen peroxide to oxygen and water: 2 H2O2 → 2 H2O + O2Manganese dioxide decomposes above about 530 °C to manganese oxide and oxygen. At temperatures close to 1000 °C, the mixed-valence compound Mn3O4 forms. Higher temperatures give MnO. Hot concentrated sulfuric acid reduces the MnO2 to manganese sulfate: 2 MnO2 + 2 H2SO4 → 2 MnSO4 + O2 + 2 H2OThe reaction of hydrogen chloride with MnO2 was used by Carl Wilhelm Scheele in the original isolation of chlorine gas in 1774: MnO2 + 4 HCl → MnCl2 + Cl2 + 2 H2OAs a source of hydrogen chloride, Scheele treated sodium chloride with concentrated sulfuric acid.
Eo = +1.23 V Eo = +1.36 VThe standard electrode potentials for the half reactions indicate that the reaction is endothermic at pH = 0, but it is favoured by the lower pH as well as the evolution of gaseous chlorine. This reaction is a convenient way to remove the manganese dioxide precipitate from the ground glass joints after running a reaction. Heating a mixture of KOH and MnO2 in air gives green potassium manganate: 2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2OPotassium manganate is the precursor to potassium permanganate, a common oxidant; the predominant application of MnO2 is as a component of dry cell batteries, so called Leclanché cell, or zinc–carbon batteries. 500,000 tonnes are consumed for this application annually. Other industrial applications include the use of MnO2 as an inorganic pigment in ceramics and in glassmaking. A specialized use of manganese dioxide is as oxid
Aniline is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine, its main use is in the manufacture of precursors to polyurethane and other industrial chemicals. Like most volatile amines, it has the odor of rotten fish, it ignites burning with a smoky flame characteristic of aromatic compounds. Aniline is a pyramidalized molecule, with hybridization of the nitrogen somewhere between sp3 and sp2; the amine is flatter than an aliphatic amine, owing to conjugation of the lone pair with the aryl substituent. Thus, the experimental geometry reflects a balance between the stabilization of lone pairs in orbitals with higher s character and better stabilization via conjugation with the aryl ring for an orbital of pure p character; the pyramidalization angle between the C–N bond and the bisector of the H–N–H angle is 142.5°. The C−N distance is correspondingly shorter. In aniline, the C−N and C−C distances are close to 1.39 Å, indicating the π-bonding between N and C.
Industrial aniline production involves two steps. First, benzene is nitrated with a concentrated mixture of nitric acid and sulfuric acid at 50 to 60 °C to yield nitrobenzene; the nitrobenzene is hydrogenated in the presence of metal catalysts: The reduction of nitrobenzene to aniline was first performed by Nikolay Zinin in 1842, using inorganic sulfide as a reductant. Aniline can alternatively be prepared from phenol derived from the cumene process. In commerce, three brands of aniline are distinguished: aniline oil for blue, pure aniline. Many analogues of aniline are known; these include toluidines, chloroanilines, aminobenzoic acids and many others. They are prepared by nitration of the substituted aromatic compounds followed by reduction. For example, this approach is used to convert toluene into toluidines and chlorobenzene into 4-chloroaniline. Alternatively, using Buchwald-Hartwig coupling or Ullmann reaction approaches, aryl halides can be aminated with aqueous or gaseous ammonia The chemistry of aniline is rich because the compound has been cheaply available for many years.
Below are some classes of its reactions. The oxidation of aniline has been investigated, can result in reactions localized at nitrogen or more results in the formation of new C-N bonds. In alkaline solution, azobenzene results, whereas arsenic acid produces the violet-coloring matter violaniline. Chromic acid converts it into quinone, whereas chlorates, in the presence of certain metallic salts, give aniline black. Hydrochloric acid and potassium chlorate give chloranil. Potassium permanganate in neutral solution oxidizes it to nitrobenzene, in alkaline solution to azobenzene and oxalic acid, in acid solution to aniline black. Hypochlorous acid gives para-amino diphenylamine. Oxidation with persulfate affords a variety of polyanilines compounds; these polymers exhibit rich acid-base properties. Like phenols, aniline derivatives are susceptible to electrophilic substitution reactions, its high reactivity reflects that it is an enamine, which enhances the electron-donating ability of the ring. For example, reaction of aniline with sulfuric acid at 180 °C produces sulfanilic acid, H2NC6H4SO3H.
If bromine water is added to aniline, the bromine water is decolourised and a white precipitate of 2,4,6-tribromoaniline is formed. To generate the mono-substituted product, a protection with acetyl chloride is required: The reaction to form 4-bromoaniline is to protect the amine with acetyl chloride hydrolyse back to reform aniline; the largest scale industrial reaction of aniline involves its alkylation with formaldehyde. An idealized equation is shown: 2 C6H5NH2 + CH2O → CH22 + H2OThe resulting diamine is the precursor to 4,4'-MDI and related diisocyanates. Aniline is a weak base. Aromatic amines such as aniline are, in general, much weaker bases than aliphatic amines. Aniline reacts with strong acids to form anilinium ion. Traditionally, the weak basicity of aniline is attributed to a combination of inductive effect from the more electronegative sp2 carbon and resonance effects, as the lone pair on the nitrogen is delocalized into the pi system of the benzene ring.: Missing in such analysis is consideration of solvation.
Aniline is, for example, more basic than ammonia in the gas phase, but ten thousand times less so in aqueous solution. Aniline reacts with acyl chlorides such as acetyl chloride to give amides; the amides formed from aniline are sometimes called anilides, for example CH3-CO-NH-C6H5 is acetanilide. At high temperatures aniline and carboxylic acids react to give the anilides. N-Methylation of aniline with methanol at elevated temperatures over acid catalysts gives N-methylaniline and dimethylaniline: C6H5NH2 + 2 CH3OH → C6H5N2 + 2H2ON-Methylaniline and dimethylaniline are colorless liquids with boiling points of 193–195 °C and 192 °C, respectively; these derivatives are of importance in the color industry. Aniline combines directly with alkyl iodides to form tertiary amines. Boiled with carbon disulfide, it gives sulfocarbanilide, which may be decomposed into phen
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
Immediately dangerous to life or health
The term dangerous to life or health is defined by the US National Institute for Occupational Safety and Health as exposure to airborne contaminants, "likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment." Examples include smoke or other poisonous gases at sufficiently high concentrations. It is calculated using the LD50 or LC50; the Occupational Safety and Health Administration regulation defines the term as "an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere."IDLH values are used to guide the selection of breathing apparatus that are made available to workers or firefighters in specific situations. The NIOSH definition does not include oxygen deficiency although atmosphere-supplying breathing apparatus is required. Examples unventilated, confined spaces; the OSHA definition is arguably broad enough to include oxygen-deficient circumstances in the absence of "airborne contaminants", as well as many other chemical, thermal, or pneumatic hazards to life or health.
It uses the broader term "impair", rather than "prevent", with respect to the ability to escape. For example, blinding but non-toxic smoke could be considered IDLH under the OSHA definition if it would impair the ability to escape a "dangerous" but not life-threatening atmosphere; the OSHA definition is part of a legal standard, the minimum legal requirement. Users or employers are encouraged to apply proper judgment to avoid taking unnecessary risks if the only immediate hazard is "reversible", such as temporary pain, nausea, or non-toxic contamination. If the concentration of harmful substances is IDLH, the worker must use the most reliable respirators; such respirators should not use cartridges or canister with the sorbent, as their lifetime is too poorly predicted. In addition, the respirator must maintain positive pressure under the mask during inspiration, as this will prevent the leakage of unfiltered air through the gaps. Textbook NIOSH recommended for use in IDLH conditions only pressure-demand self-contained breathing apparatus with a full facepiece, or pressure-demand supplied-air respirator equipped with a full facepiece in combination with an auxiliary pressure-demand self-contained breathing apparatus.
The following examples are listed in reference to IDLH values. Legend: Ca NIOSH considers this substance to be a potential occupational carcinogen. Revised values may follow in parentheses. N. D. Not determined; that is, the level is unknown, not non-existent. 10%LEL The IDLM value has been set at 10% of the lower explosive limit although other irreversible health effects or impairment of escape due to toxicology exist only at higher levels. NIOSH air filtration rating NIOSH IDLH site 1910.134 Respiratory protection definitions