Oxygen level

Another example is dissolved oxygen (DO). The amount of DO water can hold at saturation is affected by both temperature and salinity. The warmer and/or saline the water, the lower the saturation DO level. Oxygen saturation is also affected by atmospheric pressure. The saturation oxygen level decreases as elevation increases. 

Initiators, usually from 0.02 to 2.0 wt % of the monomer of organic peroxides or azo compounds, are dissolved in the reaction solvents and fed separately to the kettie. Since oxygen is often an inhibitor of acryUc polymerizations, its presence is undesirable. When the polymerization is carried out below reflux temperatures, low oxygen levels are obtained by an initial purge with an inert gas such as carbon dioxide or nitrogen. A blanket of the inert gas is then maintained over the polymerization mixture. The duration of the polymerization is usually 24 h (95). 

P ck g ing. Dry milk is packaged ia large bulk or small retail containers. A suitable container keeps out moisture, light, and air (oxygen). For dry whole milk, oxygen is removed by vacuum, and an iaert gas, such as nitrogen, is iaserted ia the heat space. An oxygen level of <2.0% is required by U.S. standard for premium quahty. 

Oxygen levels in the VGO parallel the nitrogen content. Thus, the most identified oxygen compounds are phenols and carboxyUc acids, frequendy called naphthenic acids. These may account for from ppm to neady 3% of a VGO. The presence of numerous complex naphthenic and naphtheno aromatic acid stmctures in cmde oils, especially immature forms, has been shown (34). Among the different stmctures a number of specific steroid carboxyUc acids have been identified. 

Stress Corrosion Crocking. Stress corrosion cracking occurs from the combined action of corrosion and stress. The corrosion may be initiated by improper chemical cleaning, high dissolved oxygen levels, pH excursions in the boiler water, the presence of free hydroxide, and high levels of chlorides. Stresses are either residual in the metal or caused by thermal excursions. Rapid startup or shutdown can cause or further aggravate stresses. Tube failures occur near stressed areas such as welds, supports, or cold worked areas. 

Entry into a tank that has contained any chlorinated or any easily evaporated solvent requires special procedures to ensure worker safety. The heavier vapors tend to concentrate in unventilated spaces. The proper tank entry procedure requires positive ventilation, testing for residue solvent vapor and oxygen levels, and the use of respiratory equipment and rescue harness. Monitoring the tank from outside is also important. The use of an appropriate gas mask is permissible in vapor concentrations of less than 2% and when there is no deficiency of atmospheric oxygen, but not for exposures exceeding one-half hour. Skin exposure to 1,1,1-trichloroethane can cause irritation, pain, bHsters, and even burning. Eye exposure may produce irritation, but should... 

Fire refining, the final smelting operation, removes further impurities and adjusts the oxygen level ia the copper by air oxidation followed by reduction with hydrocarbons, ammonia, or reformed gas (CO + H2). 

Fire Refining. The impurities in bhster copper obtained from converters must be reduced before the bUster can be fabricated or cast into anodes to be electrolyticaHy refined. High sulfur and oxygen levels result in excessive gas evolution during casting and uneven anode surfaces. Such anodes result in low current efficiencies and uneven cathode deposits with excessive impurities. Fite refining is essential whether the copper is to be marketed directly or electrorefined. 

Fite refining adjusts the sulfur and oxygen levels in the bhster copper and removes impurities as slag or volatile products. The fire-refined copper is sold for fabrication into end products, provided that the chemistry permits product specifications to be met. Some impurities, such as selenium and nickel, are not sufficiently removed by fire refining. If these impurities are detrimental to fabrication or end use, the copper must be electrorefined. Other impurities, such as gold, silver, selenium, and tellurium, are only recovered via electrorefining. Virtually all copper is electrorefined. 

If the fire-refined copper is to be cast into anodes for electrorefining, the oxygen content of the copper is lowered to 0.05—0.2%. If the copper is to be sold directly for fabrication, the oxygen level is adjusted to 0.03—0.05%, which is the range for tough-pitch copper. The principal reactions of fire refining are... 

A suitable means of scale-up for aerobic processes is to measure the dissolved oxygen level that is adequate in small equipment and to adjust conditions in the plant until this level of dissolved oxygen is reached. However, some antibiotic fermentations and the production of fodder yeast from hydrocarbon substrates have very severe requirements, and designers are hard-pressed to supply enough oxygen. 

Effects of Low Oxygen Levels There are many factors which can affect the abihty of human beings to adjust to lower oxygen levels. For example, two men were accidentally exposed to a low oxygen level in a vessel. One of them died, and one survived without permanent injuiy. The one who died had been in poorer general health and it is believed that this fac tor may have made the low oxygen level fatal for him, while the other person, who was in good health, survived. 

Class A—immediately dangerous to life and health based on oxygen level less than 19.5 percent and/or airborne presence of toxic or poisonous substances in concentration constituting IDLH conditions flammabihty up to 20 percent of lower flammable limit. 

Class B—Non-IDLH based on oxygen level between 19.5 and 21 percent, but classified as dangerous due to the airborne presence of toxic or poisonous substance Below IDLH level, but greater than the protection factor offered by air-purifying respirators. 

These standards applied to simple and regenerative eyele gas turbines, and to the gas turbine portion of eombined eyele steam/eleetrie generating systems. The 15% oxygen level was speeified to prevent the NOxPpm level being aehieved by dilution of the exhaust with air. 

Table 5.7 Typical effects of depleted oxygen levels in air...

Consider need for checks on oxygen levels or loss of inert medium... 

Prior to entry into large tanks containing inert medium, ensure that pipes to the tank from cryogen storage are blanked off or positively closed off purge with air and check oxygen levels. 

Ensure tliat operator exposure is below tlie hygiene standard. (Note For envuonmental monitoring, beeause of its toxieity, a CO2 analyser must be used as distinet from simply relying on eheeks of oxygen levels.)... 

Provision for monitoring and sampling, e.g. of oxygen levels, eombustible gases and airborne toxie substanees and the taking of samples from air, water and ground. 

Deoxygenated blood Blood containing hemoglobin with oxygen levels be-... 

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