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The iron content of asbestos affects important properties such as the electrical resistance of electrical insulation; because the iron content of asbestos varies by type of asbestos selected, this property is controlled for special applications.
This article discusses the iron content of various forms of asbestos. This article series describes the physical properties of asbestos including its mechanical, chemical, electrical and related properties both in pure asbestos form and when asbestos is mixed with other materials like cement or rubber.
The iron content of chrysotile asbestos may be expressed
a number of different ways, some of which are factual,
and as such serve to reveal the over-all characteristics of
an asbestos fiber so contaminated; however, other expres-
sions are mere indications of possible chemical relationships.
They offer a convenient means of representing the presence
of some compounds of iron but which do not necessarily
give any indication as to the true identity of the compound
or the properties which may be imparted as a result of its
The varieties of iron oxide which occur most frequently
in nature are ferric oxide (Fe203) and ferroso-ferric oxide
the latter being mineralogically identified as mag-
netite. The element, Fe, is rarely found in natural form, be-
cause of its readily oxidizable character; similarly, FeO is
a rarity in nature; usually it is the product of man's efforts
to produce such a compound, or it occurs as a by-product of
a metallurgical process.
The only iron compounds that directly concern the manu-
facturers of asbestos products are Fe203, Fe304, the silicates
of iron and perhaps some varieties of the hydrated iron
oxide minerals. Of these, only Fe3O4, has any marked influ-
ence on the electrical properties of products containing such
* Shaw, M. C. Asbestos Textile Institute Phila., Penn.
It is important to point out the significance of a proper
and accurate understanding with regard to the state of the iron which actually exists in the materials under investiga-
tion. An analysis report in which the Fe is mentioned as
total iron, without respect to the state or valence, means
. nothing. Similarly, to present the same information in terms
of FeO or Fe203 is equally useless, if these figures are mere
calculations based upon the total Fe content without respect
to the state of the Fe.
In such asbestos textile products as cloth, lap, roving and
paper, which are intended for use as electrical insulators,
the presence of Fe3O4 is objectionable. Such particles are
electrical conductors and may establish points of electrical
weakness in materials in which they are found. The remaining
varieties of the aforë-mentionediron bearing compounds
exert only a minor influence insofar as electrical properties
are concerned; however, occasionally they do influence the
color differences which may occur between the several vaneties
of chrysotile found throughout the world.
Perhaps the most striking failure of a chemical analysis
; to portray accurately the presence of, and the qualities to
be imparted by, Fe3O4 in particular, and the other varieties
in general, is its inability to take into account tho factor of
grain size. The grain size and distribution of Fe3O4 are as
important as the amount present. A minority of largegrains
of these impurities, well dispersed throughout an asbestos
product, can prove to be much more troublesome than the
same amount of extremely fine grained impurities.
and devices for determining the relative
magnetic iron content of asbestos have been investigated.
The results indicated quite clearly that the Mapes Analyzer
ASTM method provides the most significant and reproducible
information, provided that the proper techniques
I are adopted in making such determinations (ASTM D1118-
50T). However, it has also been established that the results
of such tests must be given proper interpretations if the in-
formation is to serve any useful purpose. The grain sizes of
the magnetite inclusions and the orientation of the grains influence
the results to a degree that tends to defy correlation.
The Mapes Analyzer does, however, serve a useful purpose
in providing rough approximations of the magnetic iron content
of a given material; when the results so obtained are
judiciously evaluated, in thelight of other contributing factors,
information of significant value can be ascertained.
In order to substantiate the belief that grain size does
markedly influence magnetic properties, a sample of known
magnetic material was fractionated into four divisions of
grain size; 0.5 gram of each fraction was thoroughly distributed
in equal amounts of a known inert material, ZnO.
Magnetic rating determinations were made on each sample;
the results of this series of tests are given in Table 2.4.
TABLE 2.4. MAGNETIC RATINGS OF ASBESTOS SAMPLES
On 35 mesh 4.40 MR *
Through 35 mesh on 80 mesh 3.70 MR
Through 80 mesh on 200 mesh 3.50 MR
Through 200 mesh 3.05 M}
* MR = Mapes Ratings
Magnetite is an oxide of iron which, under the proper
conditions, can be further oxidized and thus relieved of its
magnetic properties. Elevated temperatures, with an excess
of air, effectively provide the necessary conditions for such
oxidation. For example, magnetite heated to 420°F retains
only 80 per cent of the specific magnetism 'held at room
temperature, at 1,000°F less than 50 per cent is retained,
and at 1,080°F the magnetic properties are eliminated'
through complete oxidation and the conversion of Fe3O4 to
To demonstrate this property, samples of National Bu-'
of Standards' normal magnetite were heated to three
different temperatures and the MR value for the result-
ing materials determined. These results are indicated in
TABLE 2.5. MAGNETIC RATING VS. TEMPERATURE
Electrical Properties of Asbestos
The electrical characteristics and properties of asbestos
are important when these particular types of products are used to manufacture such electrical units as asbestos wire
The low magnetic iron content chrysotile fibers
are used in these type applications.
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 Asbestos, its Industrial Applications, D.V. Roasato, engineering consultant, Newton MA, Reinhold Publishing Co., NY, 1959, Library of Congress Catalog No. 59-12535. We are in process of re-publishing this interesting text. Excerpts & adaptations are found in InspectApedia.com articles on asbestos history, production & visual identification in and on buildings.
 "Asbestos in Plastic Compositions", A.B. Cummins, Modern Plastics [un-dated, pre 1952]
 "Asbestos in Your Home," Spokane County Air Pollution Control Authority, Spokane WA 509-477-4727 www.scapa.org provides a one-page image, a .pdf file drawing of a house warning of some possible sources of asbestos in the home. The sources are not ranked according to actual risk of releasing hazardous levels of airborne asbestos fibers and the list is useful but incomplete.
 The US EPA provides a sample list of asbestos containing products epa.gov/earth1r6/6pd/asbestos/asbmatl.htm
 "Characterization of asbestos exposure among
automotive mechanics servicing and handling
asbestos-containing materials", Gary Scott Dotson, University of South Florida, 1 June 2006, web search 3/9/2012 original source: scholarcommons.usf.edu/cgi/viewcontent.cgi?article=3505&context=etd [copy on file as /hazmat/Automotive_Asbestos_Exposuret.pdf ].
 Asbestos Identification and Testing References
Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.
Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
 Asbestos in Your Home U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
 Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print, text and images available at InspectAPedia.com).
 "Handling Asbestos-Containing roofing material - an update", Carl Good, NRCA Associate Executive Director, Professional Roofing, February 1992, p. 38-43
 EPA Guidance for Controlling Asbestos-Containing Materials in buildings, NIAST, National Institute on Abatement Sciences & Technology, [republishing EPA public documents] 1985 ed., Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460 Copy on file as - /hazmat/Asbestos_in_Your_Home_US_EPA.pdf - Asbestos in Your Home - U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
Basic Information about Asbestos, US EPA, web search 08/17/2010, original source: http://www.epa.gov/asbestos/pubs/help.html
"Handling Asbestos-Containing roofing material - an update", Carl Good, NRCA Associate Executive Director, Professional Roofing, February 1992, p. 38-43
EPA Guidance for Controlling Asbestos-Containing Materials in buildings, NIAST, National Institute on Abatement Sciences & Technology, [republishing EPA public documents] 1985 ed., Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
Copy on file as - /hazmat/Asbestos_in_Your_Home_US_EPA.pdf - Asbestos in Your Home - U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
[copy on file as /hazmat/Vermiculite_US_EPA.pdf/ Current Best Practices for Vermiculite Attic Insulation - May 2003, U.S. EPA
[copy on file as] /hazmat/Vermiculite_Health_Canada.pdf] Vermiculite Insulation Containing Amphibole Asbestos - September 2009, Health Canada
Managing Asbestos in Place, How to Develop and Maintain a Building Asbestos Operations and Maintenance (O&M) Program, U.S. EPA, web search 01/20/2011, original source: http://www.epa.gov/asbestos/pubs/management_in_place.html
Asbestos Strategies, Lessons Learned about Management and Use of Asbestos: Report of Findings and Recommendations on the Use and Management of Asbestos, 16 May 2003, US EPA, web search 01/20/2011, original source: http://www.epa.gov/asbestos/pubs/asbstrategiesrptgetf.pdf
prepared by the: Global Environment & Technology Foundation, 7010 Little River Turnpike, Suite. 460, Annandale VA 20003
Other US EPA Publications on asbestos: web search 01/20/2011, see http://www.epa.gov/asbestos/pubs/pubs.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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The HOME REFERENCE BOOK - the ENCYCLOPEDIA of HOMES, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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