Document Dv2MY1MJx7LpoKmYVvyaoZXVO

Industrial Hygiene above 5p in size usually will not remain air borne long enough to present an inhalation problem Dust may enter the air from various sources It may be dispersed when a dusty material is handled, such as when lead oxide is dumped into a mixer or a product is dusted with talc When solid materials are reduced to small sizes in processes such as grinding, crushing, blasting, shaking, and drilling, the mechanical action of the grinding or shaking device supplies a source of energy to disperse the dust formed Fumes Solid particles generated by con densation from the gaseous state, generally after volatilization from molten metals This physical change is often accompanied by a chemical reaction, such as oxidation Fumes flocculate and sometimes coalesce A fume is formed when a volatized solid, such as a metal, condenses in cool air The solid particles that make up a fume are ex tremely fine, usually less than 1 0p. In most cases, the hot material reacts with the air to form an oxide Examples are lead oxide fume from smelting, and iron oxide fume from arc welding A fume can also be formed when a material such as magnesium metal is burned or when welding or gas cutting is done on galvanized metal Odorous gases and vapors are not fumes Newspaper columnists commonly misuse this term and refer to carbon monoxide as a fume Smoke Carbon or soot particles less than 0 lp in size which result from the incomplete combustion of carbonaceous materials such as coal or oil Smoke generally contains droplets as well as dry particles Tobacco, for instance, produces a wet smoke composed of minute tarry droplets The size of the particles contained in tobacco smoke is about 0 25m AEROSOLS Liquid droplets or solid par ticles dispersed in air, that are of fine enough particle size to remain so dispersed for a period of time Mists Suspended liquid droplets gen erated by condensation from the gaseous to the liquid state or by breaking up a liquid into a dispersed state, such as by splashing, foaming, or atomizing Mist is formed when a finely divided liquid is suspended in air Examples are the oil mist produced during cutting and grinding operations, acid mists from electroplating, acid or alkali mists from pickling operations, paint spray mist from spraving operations and the condensation of water vapor to form a fog or rain Gases Normally formless fluids which occupy the space of enclosure and which can be changed to the liquid or solid state only by the combined effect of increased pressure and decreased temperature Gases diffuse Examples are welding gases, ex haust gases, and air Vapors The gaseous form of substances which are normally in the solid or liquid state (at room temperature and pressure) The vapor can be changed back to the solid or liquid state either by increasing the pressure or decreasing the temperature alone Vapors also diffuse Evaporation is the process by which a liquid is changed into the vapor state and mixed with the surrounding air Solvents with low boiling points will volatilize readily The safety professional will recognize that air contaminants exist as a gas, dust, fume, mist, or vapor in the workroom air In evalu ating the degree of exposure the measured concentration of the air contaminant is com pared to limits which appear in the published standards on levels of exposure (These are published m the next chapter) In addition to the definitions of states of matter, which find daily usage m the vocabu lary of the industrial hygienist, other terms used to describe degree of exposure are ppm --Parts of vapor or gas per million parts of contaminated air by volume mppcf-- Millions of particles of a particulate per cubic foot of air mg/mJ -- Milligrams of a substance per cubic meter of air microgramsll--Micrograms of a substance per liter of solution Annually the American Conference of 1252