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Raybestos- Manhattan
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June 1, 1972
Mr. E. W. Drlslane, Executive Secretary
Friction Materials Standards Institute, Inc
Bergen Mall Office Center, E.210
Route #4
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Paranus, N'.J. C7652
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Dear Ed:
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The..attached-material concerning- automotive emissions'of asbestos fibre was recei/ed-lroa illiiiois Institute of Technology Research Institute
yesterday and probably will be of interest to other members of the FKSZ Asbestos Study Comcdttee . I suggest that you circulate it to them.
This material was forwarded by Dr. Colin F. Harwood of IITEI as a supplement to information presented at a seminar on asbestos they conducted April 4 through 7. Very little attention was devoted to automotive emission sources during the seminar. ' .
The main issue I -would have with Dr. Harwood's conclusion would have to do with whether or not the free fibres or fibrils released from friction material decomposition are truly hazardous in. any way, and I also believe he tends to underestimate the problems involved in non asbestos containing braking systems.
Since it appears unnecessary and probably impossible to schedule an Asbestos "Study Conxittee meeting in June and I will be away the first two weeks in July, I think it might be prudent to tentatively schedule a meeting late in July, preferably during the last week. By that time -I expect there will be a number of subjects worthwhile reviewing. If you agree, kindly canvass the other members and pick a date. As far as I know, I will be available aijtine during the week of July 24. I am also open the week after that in the event this suits the others
better.
Best regards. I. H. Weaver
SCF-ALLF-04010
l'*
attachments such that the dust created is arrested at the source
and collected in filter hags. Commercial devices are available
but normally firms with a sincere interest in pollution control,
design and fabricate-their own devices. Two examples cf such
devices are shown in Figures 6 and-7. These control hoods work
on the high velocity, low volume principle and can be readily
adapted to industrial vacuum cleaner systems.
.
When arrest-at-the-source systems are not possible, tech
niques ' similar "to those employed by the asbestos spraying
*
industry may be utilized. Rules which relate more specifically
to fabrication of asbestos products may be found in such publi
cations as:
,
- ,, 1. "Recommended Practices for .Fabricating', Handling and Construction Industries, * Health, and Safety Council-Asbestos Cement Products Association.
2. "Recommended Health Safety Practices for Handling
... . and Applying Thermal Insulation Products Containing
.. . Asbestos," National Insulation Manufacturers ' *
. . Association (NIMA)...
'
3. The Asbestos Research council Guides (London. England).
Control and Safety
4. "Recommendations for Handling Asbestos," Engineering
Equipment Users Association (EEUA) , E.E.tJ.A. Hand--
. book No. 33.
*
3.3.3 Friction Material.Applications
-
Typical friction materials contain 30 to 50% asbestos and
may be up to 70%, and the industry that manufactures these ma
terials is ranked third (1969) in the consumption of asbestos
fibers. Crysotile is the preferred variety because it has
better frictional properties than amphibol asbestos and does
not exert so much wear on the opposing surface.
.
The major uses of asbestos-containing friction materials
include brake linings, brake discs and clutch facings. These
products have been applied to a wide variety of industrial and
V commercial products.
.
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Sources of Emission - Emission of asbestos from friction
materials results from normal day-to-day usage. An idea of the
scope of this source can be gained from the estimation that the
average automobile wears out 3 to 4 sets of brake linings, and ''
1 to 2 sets of clutch facings during its lifetime and that
commercial public transport vehicles wear out many more sets.
Data concerning motor vehicle brake linings for the whole of
the United States are given in the followingi
'
Vehicle miles during 1968
1,010,000,000,000
Mileage life of brake linings
. 27,500
Srake lining sets on new vehicles
10,718,000 *
Pounds of asbestos per set of brake linings
.3
Tests performed on brake linings have indicated that . under conditions of normal usage, considerable alteration of the asbestos occurs. It is reported that most of-the dust collected from brake drums appears non-fibrous and is similar in appearance to thermally degraded -asbestos. The suggestion is that high temperatures at the brake lining/drum contact points actually reach degradation levels.
Tests on brake linings, brake discs and clutches have demonstrated that the quantity of fiber emitted is some function__ of the severity of-the braking conditions (see Table 3) . Kow-- --ever, "even at-the level taf l'%, 'the "total emissions must be considerable when the total tonnage in use is considered. Further, the emissions are likely to occur at places of high density population and restricted ventilation. That is, in busy main streets of towns surrounded by large buildings.
The effect of different braking conditions and different types of friction materials on asbestos emissions is the subject of a study being sponsored by the Environmental Protection Acencv. Other studies are being conducted in California and some work on roadsides has been done at Mt. Sinai, New York. The EPA study will establish the extent and nature of the asbestos
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Table 3
ASSSSTOS EMISSIONS FROM ERAXS LININGS (Test. Results by. Electron Microcraph)
Product
-' Brand
.1 Automobile
A
drum brakes
.2 It
B
3. (1
C
4. . If
C
5. D French
6. It
7. " * German
8. ft
G
9. tt . C
10. II
H.
11. Automobile clutch
J
12. Automobile
K
disk brake *
13. Bus drum brake
L
14. M
15. Truck drum
r
brake (light)
7est'
No. of
Method _____ Samples
Friction
6
Conditions Presence of of Tcr,t-F Free Fibers
300-000
Few
Z Free Fiber*
<1
Friction Friction Friction Friction
6 250-800 None
0
5 300-700
Few
<1
1
700-900 Numerous
--10
5 300-800-
Few
<1
Friction Friction
5 300-700 5 300-800*
Few Few
<1 <1
Friction Friction Friction Dynamometer
Dynamometer
Dynamometer
Friction Friction
2 1 2* 1
1
1
2 10
100-500
600-700
100-600
normal driving
normal driving
city driving
450-550
300-800
Few Numerous
Few None
Few
None
None Few
<1 --15
<1 .0
<5
0
0 <1
Height estimated from fiber volume.
26
emitted from brake drums, disc crakes and clutches of vehicles
operating under real conditions. Hopefully the situation will
be more clearly understood at the end of those studies.
_
Emission Control Techniques
''
Emission at Overhaul - To avoid blowing the accumulated dust into the atmosphere at the time of overhaul devices have been suggested for extraction of the dust from brake and/or clutch housings by suction. Of the devices tried, a simple hand-held vacuum cleaner has proven to be the most flexible unit. Changes to the original design have been limited to the addition of a disposable paper bag inserted in the original cloth bag. The paper bag may be easily sealed before removal to prevent emission.
Substitution - Beyond the adaptation of better cleaning
practices during brake and clutch maintenance, as mentioned
above, additional controls seem to be limited to improve design
of brakeband clutch assemblies and/or substitution of other
materials for asbestos.
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.
The high temperature properties and exceptional tensile
strength of asbestos have resulted in very compact and economi
cal design. These.same unique properties which make asbestos
applicable to friction materials also make' the application of
substitute materials very difficult. The tensile strength and
modules of rigidity of asbestos as compared to several candidate
substitute materials follows:'
'
Tensile Strength lb/in/
Asbestos
550,000
Fiber yarns 180,000
Steel wool
50,000
.Mineral wool 25,000
Modulus of iciditv Ib/in 2 30,000,000 3.000,000 100,000 60,000
There is no doubt that substitution of other materials for asbestos, is .possible, but the design changes required to accom modate the stresses and temperatures involved^ would result in*
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c larger, more expensive components. Brakes - The recent adoption of disc brakes by the auto motive industry makes material substitution more plausible. ^ Disc brakes are capable of greater energy dissipation than similar- sized drum brakes because the design results in con siderably lower heating rates. This is due to the fact that at any one time the friction pad contacts only a section of the disc surface. The lower operating temperatures permit the use " of friction materials which do not contain asbestos. Another* feature of disc brake design which has reduced the need of * . asbestos materials is the lower strength requirement of the friction material.
Clutches - The substitution of other material for 'asbestos in clutch facings of'traditional design could only be done byf
changes in size and design. Two changes in clutch design which *
have reduced the retirement for asbestos-containing friction
c materials are the advent of the automatic transmission and the redesign of manual clutch friction surface. ** The clutch surface of the automatic transmission is im
mersed JLn an oil hath which virtually eliminates airborne
.
pollutants. Further, the cooling affect of the oil bath
reduces the requirement for high-temperature .capability
materials. Automatic transmission clutch facings mey he made
.from .either .sintered -faetels or fibrous cellulose materials.
Many manual clutches have redesigned friction surfaces which consist of numerous small circular pads or discs attached to the clutch face as opposed to the standard annular ring friction surface. These small pads act in the same manner as the disc brakes friction pad. Thus, lower stresses and oper ating temperatures associated with the new design reduce the need for asbestos-containing friction materials.
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10 ecificproblems
10.1 Emission Levels
In understanding control techniques and tr.eir efficiencies
it is important not tc he confused with efficiencies quoted on
a weight basis and those based on a particle count basis.
Firstly, considering efficiency based on a weight basis,
it is relatively easy to get a very high efficiency with parti
cles whose size is in excess of 5p, with a variety of control
devices- (see Figure-10) . However, the efficiency does drop off
considerably with decrease of particle size, for example, see
Figure 11 for l/i particles, (it should be noted that these
graphs refer to spherical particles - information on fibrous
particles is not presently available.)
.
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Now consider what these apparent high efficiencies mean
in terms of numbers of fibers. It can be assumed that 10
average fibers of asbestos weigh approximately l`ng.
#
If 1 g of asbestos material approaches a filter rated at
even as high as 99.999% efficiency, then the quantity passing
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3
through will be 0.00001 g. or 10 ng. And since 1 ng _a. 10
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fibers, then a total of 10 fibers will pass thxougn the filter
for every 1 g of material 'impinging upon it.
This is a situation not frequently brought out, but is very
significant when exposure levels are monitored in terms of
fibers per cubic centimeter.
.
- Thus the quoting of efficiency in terms of mass efficiency is a "red-herring" statement that flatters to deceive. It bears no obvious relation to the number of fibers being emitted.
However, based on tests which actually measure the number
of fibers being emitted, it would seem that both fabric filters
and high efficiency wet scrubbers are capable of reducing the
fiber counts to acceptable levels. British experience is that
0*2 f/cc is routine and Johns Manville finds that 1 f/cc is an
acceptable value when the results are averaged over a time
period.
-,
;. .
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The medical evidence as to the size or fiber responsible
for adverse health`effects is not positive nor is the question
of- whether fibrils of fibers are most hazardous. Until the
,,
medical questipns are fully resolved,, it would seem premature
to impose inflexible or overly rigid regulations..
This has been the view held by the Federal occupational
health authorities in assessing their standards. It would seem
that thgi approach in limiting exposure to that- which is possi
ble using good modern technology is sensible. 'The same may be
said for their monitoring techniques.
'
. 10.2 Water Pollution
. Recycling of waste water is possible and is practiced in. certain segments of the industry. The question of the damage done to streams, rivers, and lakes by indiscriminant dumping of asbestos containing waste waters needs careful study. One must remember it is a natural material which will appear in water in any case. On the other hand, there is evidence that asbestos particles ingested into the stomach may cause stomach cancer. _
Again, until medical evidence is clear, it would seem ' sensible to recycle water whenever this can be accomplished.
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