(1) Field of the Invention
This invention relates to compositions and methods for removing asbestos-containing materials from their associated substrates.
(2) Description of the Prior Art
Until recent times, exposure to asbestos was recognized as a problem only from the standpoint of occupational health hazards to asbestos workers. Now, however, it is generally accepted that serious exposure problems also can occur in buildings constructed with fireproofing, insulation and decorative materials made at least in part from asbestos. Asbestos-containing coating and plastering materials are regarded as being particularly hazardous since they tend to become friable, and hence easily entrained into the air, as they deteriorate with age.
Concern about environmental contamination by asbestos-containing materials has manifested itself in many ways including the promulgation of numerous Federal Regulations dealing with the subject. For example, one widely quoted OSHA asbestos exposure standard calls for concentrations of less than 2 fibers/cc.times.8 hours with no peaks greater than 10 fibers/cc.times.15 minutes. Such concerns are well taken. Asbestosis, a disease of the lungs produced by inhalation of asbestos fibers, has come to be recognized as being associated with an extreme liability to lung cancer as well as being an often fatal malady in its own right. Moreover, detection of such asbestos-related diseases is impeded by the fact that the latency period between exposure and appearance of such disease is sometimes as much as 25 years.
Unfortunately, asbestos has been widely used in the past owing to its excellent fire inhibiting qualities. For example, it was the practice for many years to spray or brush asbestos-containing coating materials onto structural steel to retard structural collapse in case of fire. Many plaster formulations also were provided with asbestos as a fireproofing measure. Asbestos-containing materials have also been coated on ceilings and walls for thermal and acoustic insulation purposes. Many of these insulation materials used in the past were comprised of mixtures of asbestos and mineral rock, slag-wool or fiber glass. Other formulations incorporated asbestos into wood pulp, paper fibers and non-fibrous binders such as vermiculite, plaster of Paris, perlite and clay. Asbestos has also been widely used in decorative and textured spray finishes and paints. The asbestos content of these materials was usually in the range of about 5 to about 50 percent by weight. They usually were applied in layers less than about one inch thick and very often are found in coating layers less than about one quarter inch thick.
Over the years many of these asbestos-containing materials have become friable--that is they have deteriorated to such an extent that they have become flaky or dust-like and hence capable of easily being entrained in a building's atmosphere. Furthermore, even though the finish of many asbestos-containing coatings and plasters may seem hard, it is often the case that asbestos fibers, which are invisible to the naked eye, come through the finish and are released from such apparently hard coating materials, particularly as they age. Asbestos-containing materials have other bad attributes as well. Asbestos fibers are very persistent as well as very pernicious. They are not easily degraded or destroyed and they tend to persist in the environment almost indefinitely. Finally, the size and shape of asbestos fibers are such that they possess certain aerodynamic qualities. They can travel great distances and remain suspended in air for very long periods of time. Moreover, asbestos fibers that do settle to the floor are easily stirred up by pedestrian traffic and the like and reintroduced back into a building's environment.
Given the proportion of our residential, industrial and commercial building stock that has been made with asbestos-containing materials, and given the relatively recent recognition of the severity of the health hazards associated with the release of asbestos fibers into their atmospheres, many methods have been proposed to deal with asbestos pollution problems in buildings now in use. Such methods generally fall into two broad categories, encapsulation and removal. In the case of encapsulation, the asbestos-containing material should be coated with sealants meeting Environmental Protection Agency (EPA) codes and regulations. See generally: Guideline For The Use of Sealants on Asbestos-Containing Materials, Prepared by Mr. Forest Reinhardt, Office of Toxic Substances, United States Environmental Protection Agency, 1980. If done properly, encapsulation permits the asbestos-containing material to remain safely in place for longer periods of time than it otherwise could. However, at best, encapsulation represents a temporary measure since sealants also will deteriorate with time.
Unfortunately, encapsulation methods are largely ineffective where the asbestos-containing material has undergone significant physical damage due to impacts and/or aging. This condition is prevalent in many older buildings. In such cases physical removal is the only safe alternative. Removal procedures require that all asbestos-containing materials be taken off their underlying substrates, carefully collected and disposed of, preferably by burial.
To date no adequate chemical removal procedures have been developed. Consequently, removal, by use of hand held impact and cutting tools, is the only viable removal method for asbestos coating and plastering materials. Vacuum tools have been tried, but the adhesive bond between most asbestos-containing materials and the underlying surfaces upon which they are coated or plastered are usually much stronger than the vacuum capabilities of ordinary vacuum equipment. Moreover, many areas are inaccessible to all but the smallest of tools. Hence scraping, chiseling and scoring, usually by simple hand tools, remains the most common method of mechanical removal.
Even more vexing is the fact that many asbestos-containing materials tend to pulverize upon impact or scraping rather than shear off in large pieces at the interface between the asbestos coating material and the substrate. Not only do these conditions greatly increase hand labor requirements, but they also result in heavy asbestos dust contamination. Work crews and neighboring personnel must be carefully protected against it. This usually involves great inconvenience and expense.
One method of dealing with such dust contamination problems during removal operations involves a simple wetting operation. Water is sprayed on the coating or plaster which is about to be removed in order to lower the friability of the asbestos-containing material and to reduce the aerodynamic capabilities of any released asbestos fibers. Unfortunately, water spraying is not a particularly satisfactory solution to the problem. Simple water spraying, at best, provides a slow, incomplete penetration of the asbestos-containing materials, and it often produces water damage to the building as it runs off of the surfaces being sprayed. Such water run-off not only creates water damage and clean-up problems, it also creates another distinct safety problem. Asbestos fibers may be carried to other areas by the water. Once there, the asbestos fibers can dry out and become reintroduced into another, distant environment.
In response to these problems, aqueous solutions containing various surfactants have been used to aid wet removal procedures of this type, In the presence of such surfactants, water penetration into the asbestos-containing fiber is somewhat improved. Hence less water runs off and less asbestos-containing dust is created. Common surfactants used for these purposes have included polyethylene oxide condensates of alkyl phenols; the condensation products of aliphatic alcohols and ethylene oxide; the condensation products of ethylene oxide with a hydrophobic base formed by the condensation of propylene oxide with propylene glycol; condensation products of amines, amides or mercaptans with ethylene oxide or propylene oxide; products formed by reacting ethanolamines with fatty acids; amine oxide surfactants; phosphine oxide surfactants and sulfoxide surfactants. Notwithstanding these advantages such surfactant treatments suffer from at least one of the drawbacks encountered with treatments based upon the use of water alone, i.e., following run-off and evaporation, asbestos fibers can become reentrained in the air at distant locations.
Consequently, various other asbestos stripping compositions have been proposed to deal with these asbestos dust, water damage and run-off problems. By way of example, U.S. Pat. No. 4,347,150 teaches an asbestos stripping composition which provides for a wet removal method which produces much less water run-off and significantly lowers the dust created during the wet removal operations. Such asbestos removal compositions often are supplied as two component formulations which are prepared just prior to use. The first component usually comprises an aqueous silicate dispersion of selected alkali metal silicates blended with a cationic or nonionic surfactant. The second component usually comprises some form of an acrylic latex composition containing a reagent that is reactive with the alkali metal silicate of the first component formulation. Common reagents used for this purpose include hydroxycarboxylic acids and salts of organic acids, e.g., gallic acid, citric acid and tartaric acid.
The aqueous silicate component is prepared by blending potassium silicate or a mixture of potassium silicate and sodium silicate with a cationic surfactant such as amine salts, fatty esters of primary, secondary or tertiary hydroxyalkyl amines or with nonionic surfactants such as polyethylene oxide condensates of alkyl phenols, the condensation products of aliphatic alcohols and ethylene oxide. The acrylic polymer of the second composition is usually selected from the group consisting of homopolymers and copolymers of lower alkyl esters of acrylic acid or lower alkyl esters of an alpha-lower alkyl acid or mixtures thereof. Again, the two components are usually stored separately for increased storage life and mixed shortly before application.
However, because of the relative complexity and expensive nature of some of their component ingredients, formulations of this type are relatively expensive. They also require a great deal of time and agitation energy to effect the reaction of the alkali metal silicates of the first component with the hydroxycarboxylic acid, salts of organic acids, etc., of the second component. Of even more import to the teachings of this patent application, the end products of the above-noted silicate/acrylic latex formulations are intended to be used in a wet condition throughout the ensuing removal operations. The wet condition produced by these formulations does not last for more than a few hours. Hence the work surface may have to be resprayed in order to keep down asbestos dust. Moreover, the ability of these formulations to penetrate to the deepest regions of the asbestos-containing material is somewhat curtailed by the tendency of these formulations to dry before complete penetration of many asbestos-containing materials. Hence the asbestos-containing materials they partially penetrate are not ptarticularly inclined to break away from their substrates at the substrate/asbestos material interface and/or break in relatively large pieces. At best, the application of these silicate/acrylic latex formulations tends to produce asbestos-containing materials which normally break away in localized, small wet clumps rather than at the substrate interface. Furthermore, to the extent these formulations fail to completely penetrate the asbestos-containing material, dust will be created from the remaining dry material. These characteristics tend to greatly add to the safety considerations and the labor costs of any given asbestos removal operation.