Oxygen deficient

A basic research study on combustion of sulfur led to the postulation that sulfur trioxide may actually be the primary combustion product and that sulfur dioxide may then be produced by the further reaction of sulfur trioxide with sulfur vapor ki the oxygen-deficient region of the flame (261). 

Both anatase and mtile are broad band gap semiconductors iu which a fiUed valence band, derived from the O 2p orbitals, is separated from an empty conduction band, derived from the Ti >d orbitals, by a band gap of ca 3 eV. Consequendy the electrical conductivity depends critically on the presence of impurities and defects such as oxygen vacancies (7). For very pure thin films, prepared by vacuum evaporation of titanium metal and then oxidation, conductivities of 10 S/cm have been reported. For both siugle-crystal and ceramic samples, the electrical conductivity depends on both the state of reduction of the and on dopant levels. At 300 K, a maximum conductivity of 1 S/cm has been reported at an oxygen deficiency of... 

TABLE 26-25 Effects of Breathing Oxygen-Deficient Atmospheres... 

SOURCE Air Products and Chemicals Go., Dangers of Oxygen Deficient Atmospheres, Allentown, Pa., 1988, and American Standards Institute, Report No. 788. 

An oxygen deficiency leads to the burning of ammonia to nitrogen according to... 

Even if the device has been properly calibrated for the particular gas in air, some analyzers such as catalytic bead types will not function in oxygen deficient atmospheres containing less than about 10 vol% oxygen. Some portable analyzers are supplied with antistatic tubing but others are supplied with nonconductive tubing such as Tygon. 

HAZARD The inherent property of a substance capable of causing harm (e.g. toxicity, radioactivity, flammability, explosivity, reactivity, instability). In a broader context anything that can cause harm, e.g. electricity, oxygen-deficiency, machinery, extreme temperature. 

OXYGEN DEFICIENCY Depletion of oxygen content in an atmosphere to below the normal 21%. Exposure to <18% must not be permitted. Concentrations 6% to 10% oxygen can lead to loss of consciousness. 

The consumption of oxygen due to atmospheric corrosion of sealed metal tanks may cause a hazard, due to oxygen-deficiency affecting persons on entry. 

Exposures to chemicals, resulting in toxic effects or oxygen-deficient atmospheres, may arise in a variety of industrial situations. A summary of common sources is given in Table 5.18 clearly this is not exhaustive since exposure may result whenever materials are mixed, machined, heated, dispersed or otherwise processed or used. 

Operation in confined spaces Improper isolation From residues Oxygen deficiency (inherent, from purging or from rusting)... 

For entry into a confined space which may contain toxic chemicals or be oxygen deficient. Refer to Figure 13.1. 

Entry into a confined space requires strict control (page 417). Whenever oxygen deficiency may be encountered air quality checks should be made and appropriate breathing apparatus used. 

Even non-toxic gases are potentially hazardous owing to asphyxiation (oxygen deficiency). Irrespective of material, all equipment must be adequately designed to withstand process pressures. 

LPG is considered to be non-toxic witli no chronic effects, but the vapour is slightly anaesthetic. In sufficiently high concentrations, resulting in oxygen deficiency, it will result in physical asphyxiation. The gases are colourless and odourless but an odorant or stenching agent (e.g. methyl mercaptan or dimethyl sulphide) is normally added to facilitate detection by smell down to approximately 0.4% by volume in air, i.e. one-fifth of the lower flammable limit. The odorant is not added for specific applications, e.g. cosmetic aerosol propellant. 

Rescue of any person from a confined space where dangerous fumes, or an oxygen-deficient atmosphere, may be present is prohibited without wearing appropriate safety equipment... 

Vapor Density (VD) — the mass per unit volume of a given vapor/gas relative to that of air. Thus, acetaldehyde with a vapor density of 1.5 is heavier than air and will accumulate in low spots, while acetylene with a vapor density of 0.9 is lighter than air and will rise and disperse. Heavy vapors present a particular hazard because of the way they accumulate if toxic they may poison workers if nontoxic they may displace air and cause suffocation by oxygen deficiency if flammable, once presented with an ignition source, they represent a fire or explosion hazard. Gases heavier than air include carbon dioxide, chlorine, hydrogen sulfide, and sulfur dioxide. 

Anoxia Anoxia is the absence of oxygen in inspired gases or in arterial blood and/or in the tissues. This is closely related to hypoxia, which is a severe oxygen deficiency in the tissues. One can think of anoxia as the most extreme case of hypoxia. 

The employer is required to identify hazardous airborne contaminants that employees may inhale and make a reasonable estimate of employee exposure in determining the appropriate respirator for employees to use. Oxygen-deficient atmospheres and those atmospheres that are not or cannot be estimated should be treated as IDLH environments. 

Oxygen-deficient An atmosphere consisting of less than 19.5% oxygen. 

Simple asphyxiant Substance that displaces air, producing an oxygen-deficient at-mosphete. 

---