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IS 9691:1980 is the Indian Standard (BIS) for method of test for length distribution (wet classification of fibre length) of chrysotile asbestos fibre using bauer mcnett classifier. This standard specifies the laboratory method for determining the length distribution of chrysotile asbestos fibres. The procedure involves wet classification using a Bauer-McNett classifier, which separates a fibre sample into different length fractions by passing a water suspension of the fibres through a series of standard screens.
Method of test for length distribution (wet classification of fibre length) of chrysotile asbestos fibre using Bauer Mcnett classifier
! This standard is for a material (asbestos) that is a known carcinogen and is now heavily regulated or banned in many applications. Extreme health and safety precautions, including appropriate PPE and ventilation, are mandatory.
! The Bauer-McNett classification result is a critical quality control parameter for asbestos fibres, as fibre length significantly influences the mechanical properties of end products like asbestos-cement sheets and pipes.
! This standard may be withdrawn or superseded by health and safety regulations. Users should verify its current status with BIS and relevant environmental/health authorities.
Standard Test Method for McNett Wet Classification of Asbestos Fiber
Direct equivalent test method for determining asbestos fiber length distribution using the same apparatus.
ISO 3613:1976International Organization for Standardization (ISO), International
HighWithdrawn
Determination of length of asbestos fibres by the McNett wet classification method
Specifies the same McNett wet classification method for asbestos fibres, serving as a historical direct equivalent.
AIA RTM1Asbestos International Association (AIA), International
MediumWithdrawn
Dry-Mixing and Wet-Sieving Test for the Determination of the Length Distribution and Content of Unopened Fibre Bundles in Asbestos Fibre
A widely-used industry method that also employs wet-sieving, though procedures can vary slightly.
Key Differences
≠The specified water temperature in IS 9691 is 27 ± 2 °C, reflecting Indian ambient conditions, whereas ASTM D2589 specifies 75 ± 5 °F (24 ± 3 °C) and ISO 3613 specifies 25 ± 5 °C.
≠IS 9691 specifies the water flow rate directly into each classifier tank (545 ± 10 ml/min), similar to ISO 3613. In contrast, ASTM D2589 specifies the control method by maintaining a constant water head of 3 inches (76 mm) above the overflow.
≠IS 9691:1980 is a static standard that has not been revised, while ASTM D2589 underwent several revisions before its withdrawal in 2013, potentially incorporating minor procedural refinements or updated cautionary notes not present in the Indian standard.
Key Similarities
≈All standards mandate the use of the same fundamental apparatus: the Bauer-McNett classifier, consisting of a series of agitated tanks in a cascade arrangement.
≈A critical similarity is the specification of the same standard stack of screens (Tyler series): No. 4, No. 14, No. 35, and No. 200 mesh, which defines the length fractions.
≈The core test parameters are identical across the standards, specifying a 10 g test specimen and a test duration of 20 minutes.
≈The method for calculating and reporting the results is consistent, requiring the mass of fibres retained on each screen to be dried, weighed, and expressed as a percentage of the original sample mass.
≈All standards specify the same agitator speed of 587 ± 1 rpm for the classifier paddles, ensuring consistent kinetic energy is applied to the fibre slurry.
Parameter Comparison
Parameter
IS Value
International
Source
Test Specimen Mass
10 ± 0.05 g
10 ± 0.05 g
ASTM D2589-09
Test Duration
20 min
20 min
ASTM D2589-09
Agitator Speed
587 ± 1 rpm
587 ± 1 rpm
ASTM D2589-09
Standard Screen Series (Tyler)
4, 14, 35, 200 mesh
4, 14, 35, 200 mesh
ASTM D2589-09
Water Temperature
27 ± 2 °C
24 ± 3 °C (75 ± 5 °F)
ASTM D2589-09
Water Flow Rate Control
545 ± 10 ml/min into each tank
Maintain constant head of 3 in. (76 mm)
ASTM D2589-09
Classifier Tank Volume
Not explicitly stated, but based on standard apparatus design
4.5 U.S. gal (17.0 L)
ASTM D2589-09
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Test specimen mass10 ± 0.05 g
Classifier tank capacity22.5 litres
Water flow rate into each tank11.35 ± 0.20 litres/min
Classifier impeller speed580 ± 20 rev/min
Disintegration period20 min
Standard screen mesh sizes4, 14, 35, and 200 mesh
Key Formulas
Percentage retained on a screen = (Mass of fibre on screen / Total initial mass of sample) x 100
To provide a standardized test method for measuring the fibre length distribution of chrysotile asbestos using a Bauer-McNett classifier.
What equipment is specified for this test?+
A Bauer-McNett classifier, along with a set of standard screens (typically 4, 14, 35, 200 mesh), a drying oven, and an analytical balance (Clause 4).
What is the principle of the Bauer-McNett test?+
It is a wet classification method. A water suspension of asbestos fibres flows sequentially through a series of tanks, each fitted with a progressively finer screen, to separate the fibres by length.
How much asbestos sample is needed for a single test?+
A test specimen of 10 ± 0.05 grams is specified (Clause 6.1).