Lead-based paint rates

Cardiovascular effects have been noted in occupationally exposed workers after exposure to high levels of lead following exposure durations of as short as 4 weeks. Construction workers (race not specified) using oxyacetylene torches to cut a metal bridge that had been painted with lead-based paint were reported to exhibit increases in heart rate and blood pressure after 4 weeks of exposure (Marino et al. 

The NIST research on existing test kits shows that existing test kits cannot reliably determine that lead is present in paint only above the statutory levels because the kits are sensitive to lead at levels below the federal standards that define lead-based paint, and therefore are prone to a large number of false positive results (i.e., a positive result when regulated lead-based paint is, in fact, not present). The NIST research found that such false positive rates range from 42 to 78%. This means that the currently available kits are not an effective means of identifying the 76% of homes built between 1960 and 1978 that do not contain regulated lead-based paint. 

These eleaning units were evaluated for their individual qualities and eompared their ability to remove lead-based paint. The maximum brush (vacuum cup) diameter indieates the relative eleaning rate for eaeh unit, sinee the brush is in eontaet with the paint and the abrasive material flows within the brush. The actual cleaning rate is a funetion ofthe operator s teehnique and the effectiveness of the abrasive material. 

A protective mask (fresh air or equivalent) is recommended for workers removing lead-based paint with power tools. Cleaning rates of 14—18 ft. /hr were reported by Bloemke at a cost of 3.05/ft.2 At the time of writing, reliable figures for lead-based paint abatement using hand-held power tools in residential sfructures is not available, but they are being generated. 

The rate of lead-based paint removal was not significantly affected by film thicknesses within the ranges indicated, since the diameter of the abrasive particles were larger than the coating thicknesses and quickly penetrated to the substrate surfaces. 

The degree of unsaturation in these oil-modified alkyds was controlled by the amount and type of unsaturated acid used in the formation of the polyester. These unsaturated polymers cured or "dried" through auto-oxldatlon by oxygen from the air which reacted with the unsaturated carbon atoms on the surface of the freshly deposited film. This crosslinking reaction, like that of the "drying" of oil-based paints, was catalyzed by heavy metal salts, such as lead or cobalt salts of organic acids. Alkyds, which are some of the most Important paint resins, are produced at an annual rate in excess of 300 thousand tons. 

Ordinary paints may be permeable to oxygen and water vapor (see Chap. 13), and though they may slow the rate of corrosion, they cannot prevent it completely. Hence, special paints with chromates or red lead (Pb304) have been used for many years as a protective coating for steel. Polymeric resins, though more expensive than the linseed oil-based paints, last longer and thus are more effective. 

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

Many tests are based on constant condensation or humidity. Incidentally, constant condensation is not the same as humidity testing. Condensation rates are higher in the former than the latter because, in constant condensation chambers, the back sides of the panels are at room tempaature and the painted side faces water vapor at 40 C. This slight temperature differential leads to higher water condensation on the panel. If no such temperature differential exists, the conditions provide humidity testing in what is known as a tropical chamber. The Cleveland chamber is one example of condensation testing a salt spray chamber with the salt fog turned off, the heater turned on, and water in the bottom (to generate vapor) is a humidity test... 

Lead salts of organic acids, the original driers, function as polymerization catalysts throughout the entire paint film depth in contrast, cobalt salts function as surface driers. Hence, until recently, combinations of lead and cobalt driers have been used to achieve a uniform drying rate. Manganese and zirconium salts may be used in place of lead. Many organic acids have been used to form these heavy metal salts, but the most widely used salts are naphthenates, which are based on naphthionic acid, a residue of petroleum resinous. Other acids used to produce driers are octoic, tallic, rosin, and linolenic acids. 

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