CHAPTER 10 SOLUTIONS TO END-OF-CHAPTER EXERCISES
10.1 Batch process hazards: Open handling is
reduced, reducing the exposure of materials to the air; batches of material
sometimes must sit idle, awaiting processing.
Continuous process hazard:
Mechanical handling equipment may increase contamination levels.
10.2. An
ordinary household ventilation fan is useful for diluting the concentration of
air contaminants at a particular workstation. Dilution ventilation is a
recognized method of reducing concentrations to a safer level. However, such
dilution disperses the contaminant throughout the plant and increases the
background level of contamination. If other processes also add to the
contamination, it may ultimately be necessary to remove the contaminant from
the air. It will be more difficult to remove later, after it has dispersed
throughout the plant. Dilution ventilation is somewhat similar to “sweeping
dirt under the rug.”
10.3 An ordinary vacuum cleaner has the
advantage of focusing the ventilation on the source and removing the
contaminant before it has an opportunity to disperse into the ambient air in
the plant. However, ordinary vacuum cleaners do not have the filtering
capability to remove most dangerous contaminants, so they will simply return
the contaminated air into the plant from the exhaust side of the vacuum
cleaner. Another disadvantage to the focused vacuum-cleaner approach is that
the concentrated force of the air stream may blow papers or interfere with the
process.
10.4. Pull systems produce a negative
pressure within the contaminated air discharge duct. Thus, leaks in the duct,
if any, will result in plant air being drawn INTO the duct. Push systems
produce a positive pressure within the contaminated air discharge duct. Any
leaks in such a duct will introduce contaminated air back into the ambient air
in the plant.
10.5. A manometer is an instrument used to
detect differences in pressure. Manometers are useful in ventilation systems to
detect differences in pressure across a filter. An increase in pressure
differential across a filter in a ventilation system is a direct indication
that the filter has clogged or built up a resistance due to the collection of
dust, dirt, or process contaminants. An alarm can be set to trigger upon a
threshold pressure differential detected by the manometer.
10.6. Solution method 1: Design and install
systems to filter and purify the contaminated air so that it can be recycled
back into the plant atmosphere.
Solution method 2: Introduce the
makeup air for the exhaust system adjacent to the point of origin for the
contaminant. The makeup air introduced at the point of operation may not need
any heating or cooling, as it will be immediately removed by the exhaust
ventilation system.
Solution method 3: Use a heat
exchanger to warm (or cool) makeup air by passing it through the heat exchanger
in close proximity to the heated (or cooled) exhaust air.
10.7. Centrifugal devices (sometimes called
cyclones)
Electrostatic precipitators
Wet scrubbers
Filters (fabric or bag-type)
10.8. Pitch and pressure intensity of the
sound wave. Of the two, pressure intensity is the more dangerous characteristic
of sound. Even though the peaks of pressure intensity can be dangerous, the
human ear can withstand, without damage, sound pressures 10,000,000 times as great as the faintest
sound it can hear.
10.9. Ionizing and nonionizing radiation,
with ionizing radiation being the more dangerous of the two. X rays are an
example of ionizing radiation that can occur in the workplace.
10.10. Some workers are concerned with
radiation (nonionizing) from computer terminals, but the principal hazard with
computer terminals is musculoskeletal disorders, not radiation.
10.11. In this problem we are given the SLM
readings and must work backwards to infer the sound output of either of the two
identical generators.
(a)
One generator on: SLM reading =
83.6 dBA
No generators on (background noise):SLM
reading = 81 dBA
Difference = 2.6 dB
This difference is used in Table
10.1, right-hand column, to infer that the decibel difference in sound output
between the background noise and one generator is 1 dB (left hand column). The louder of the two sources is the
background noise at 81 dBA, since this was the value to which 2.6 dB was added
to result in 83.6 dBA. Therefore the
noise output of each generator is 81 - 1 = 80 dBA. When the second generator is turned on, it
will add another 80 dBA to the 83.6 dBA.
83.6
80
Difference
= 3.6
Table 10.1 (left hand column) does
not show an entry for a difference of 3.6 dB, but linear interpolation can be
used as an approximation:
3.6
- 3 = x - 1.8
4 - 3
1.4 - 1.8
x = 1.56
Therefore
83.6 + 1.56 = 85.16 dBA with both machines on
(b) PEL = 90 dBA
Since
85.16 < 90, PEL is not exceeded.
Since
85.16 > 85,
(c) From Table 10.2 and using
linear interpolation (as in part [a]):
dBA Hrs. Ref. Duration
83.6
4 19.48
85.16 4 15.664
D = S Cn = 100
4 + 4
Tn 19.48 15.664
D
= 46.07% < 100% PEL not
exceeded
D
= 46.07% < 50%
(d) For 1 generator: the dBA would be 80 dBA
(from
solution in Part [a])
For
2 generators: 80 + 3 (from Table 10.1) = 83 dBA
10.12. (a) machine
1 86 dB
machine
2 -80 dB
6 dB ® dB = 1.0
86
93
+
1.0 +
1.0
87.0
dB 94.0 dB
machine
3 93.0 machine 4 70.0
dB
6 dB ® dB = 1.0 24.0 dB ®
dB = negl.
Therefore,
combined noise level is 94 dBA.
(b) First we determine the
combined noise level of machines 1, 2, and 4. machines 1 and 2: 87 dBA (from
part [a] above)machine 4 at 70 dBA is of negligible consequence since the
difference (87 - 70 = 17 dB) does not appear in Table 10.1.
OSHA 8-hr PEL = 90 dBA
So machine 3 can add only 90 - 87
= 3 dB to the exposure. From Table 10.1
(or by the Rule of Thumb) we know that 3 dB are added when the sound outputs of
two sources are equal (0 dB difference).
Therefore machine 3 noise must be reduced to 87 dBA, equivalent to the
combined outputs of machines 1, 2, and 4.
This constitutes a reduction of 93 - 87 = 6 dB from the current noise
output of machine 3.
6 dB = 2 x 3 dB so the absolute
noise output of machine 3 must be halved twice, or reduced by a factor of 4.
Thus the original distance of 5
feet from machine 3 to the worker must be increased to reduce the sound by a
factor of 4. The sound intensity is
reduced as the square of the distance, so
52/d2
= 1/4
d2
= 52 x 4 = 25 x 4 = 100
d
= 10 feet
Note that we have doubled
the distance from 5 feet to 10 feet and the resultant sound is thus reduced by
a factor of 4.
10.13. (1)
Change the process that produces the contaminant
(2) Change the materials used in
the process
10.14. "Makeup
air" is air to replace the exhausted air in a ventilation system.
10.15. Since the difference between 99dB and
65dB is so great, the background noise can be considered as negligible. So we have
99 dB for 10 machines
-3
96 dB for 5 machines
-3
93 dB for 2.5 machines
-3
90 dB for 1.25 machines
Therefore, 9 machines would have
to be shut down to meet the 90 dB standard.
10.16. The 55 dB ambient noise level is a
negligible contribution to the total noise level when the machine is on. Therefore the noise level would decrease
according to the square of the distance of the machine:
Abs. sound level at 3 ft 122 144
Ratio
= ----------------------------- = ---- = ---- = 16
Abs. sound level at 12 ft 32
9
So the absolute sound level will
decrease by a factor of 16. Since 16 = 24,
the sound level will be cut in half 4 times.
Every time the absolute noise level is halved, the sound level decreases
by 3 dB. Therefore, after the machine is
moved to a distance of 12 feet, the SLM will read 90 dB - (4x3 dB) = 78 dB.
10.17. 20% x 90 tons x 2000 lbs = 36000 lbs. (liquid)
ton
Vapor released = 36000 lbs x 450 = 157,282 ft3
103 lbs/ft3
PEL
(chlorine) = 1 ppm
(Appendix A.1)
Vapor
released < PEL of 1 ppm
Room
volume
157,282
ft3/vol < 10-6
Vol > 157,282 ft3
10-6
Vol > 157,282 x 106 ft3
Vol > 1.57 x 1011 ft3
Floor
Space (in square miles) = Volume x [
1 mile]2
Ceiling
Height [5280 ft]2
=
1.57 x 1011
30 x 52802
=
.523 x 1010 = 188 square miles
5.282 x 106
10.18. (a) dB hrs
86 1
84 2
81 1
101
1
75 3
8
Using
Table 10.2:
n Cn
1 2 1 1
D
= 100 S ----- = 100 -----
+ ----- + ----- + ---- = 80.47%
i=1 Tn 13.9 18.4 27.9
1.7
Since
80.47% < 100, PEL is not exceeded.
(b)
yes (since 80.47% > 50%)
(c)
yes
(d) no (unless the employee has
experienced a permanent threshold shift)
(e) Afternoon; the 101 dBA
contributes more than all other exposures combined. Comparison is as follows:
Cut
sound in morning: 86 -- 83; 84 -- 81; 81 -- 78
n Cn 1 2 1
D
= 100 S --- = 100 ---- + ---- + ---- = 70.73%
i=1 Tn
21.1 27.9 1.7
Cut
sound in afternoon:
n Cn 1 2 1
1
D
= 100 S --- = 100
---- + ---- + ---- + ---- = 60.11%
i=1 Tn
13.9 18.4 27.9 2.6
10.19. 2 Enclose
the noise source with a barrier that reduces the noise level by 50%.
1 Position
the operator at a distance twice as far from the source of the noise.
3 Rotate
personnel so that each worker is exposed to the noise source for only one-half
shift.
4 Provide ear protection that cuts the noise
level by one half.
Moving the operator away (twice as
far) from the noise is best because this change will reduce the noise exposure
by a factor of 4 (6 db), whereas the other three alternatives only reduce the
noise exposure by a factor of 2 (3 db reduction reduces the absolute sound
pressure by a factor of 2). Second in
priority is the barrier because it would be considered an engineering control. Third in priority would be rotating
personnel, an administrative or "work practice" control. Last in priority would be ear protectors,
which would represent personal protective equipment.
10.20. PEL liberated 5
---- =
--------- = ---
106
exhaust E
5(106) 5(106)
E
= -------- = ------- = 5,000 ft3/hr
PEL
1000
10.21. Instead of silica (for blasting), use
steel shot.
Instead of lead-based paint, use
iron oxide pigments.
Instead of freon (as a
propellant), use propane.
Instead of acetylene (for
welding), use natural gas, if flame temperature is hot enough.
10.22. Often operating personnel ignore such
alarms as red lights. Even when the
alarm is an audible type, operators and/or maintenance personnel may ignore the
signals or even deliberately disconnect the wiring to the alarms as an
expediency.
10.23. The purpose is to save energy costs by
allowing the transfer of energy between exhaust air and makeup air, that is,
from exhaust air to makeup air in the winter months and from makeup air to
exhaust air in the summer months. The
method is especially effective in cold climates in which much energy is lost
via exhaust air. The drawback to the
approach is that it places contaminated air in close proximity to clean makeup
air. If there are leaks in the heat exchanger,
cross-contamination can result.
10.24. Exhaust ventilation is being used with
insufficient sources of makeup air, probably due to the need to open some
windows or doors.
10.25. X-rays
10.26. (a) For the design of a ventilation
system to protect against safety hazards the appropriate physical
characteristic is LEL, "lower explosive limit," which, for ethylene
glycol, is 3.2%. The ventilation system
must introduce sufficient makeup air to maintain a dilution of the ethylene
glycol to less than 3.2%. Although a
large room size might accommodate the contamination for a short period, in the
long run the ventilation system must keep up with the rate of contamination
produced by the process, regardless of the dimensions of the air volume within
the plant. Therefore,
2.4 ft3 =
3.2%
vent
vent =
240/3.2 = 75 ft3/hr
(b) To deal with the health hazard
the ventilation system must keep the concentration of ethylene glycol at least
below the PEL and should be designed to keep it below the action level. The PEL for ethylene glycol is shown in the
problem statement to be 50 ppm (ceiling)[1],
so the
2.4 ft3 = 25
ppm =
0.000025
vent
vent = 2400000/25
= 96000 ft3/hr
(c) Although the room volume of
the plant would not affect the design of the general dilution ventilation
system to deal with the ethylene glycol hazard, it would determine how many
room changes per hour the ventilation system would effect, as follows:
Room changes/hr = vent
per hr/ Room air volume
=
96000 ft3/hr = 0.5
12000 ft2 x 16 ft
10.27. Plan A: Doubling the distance reduces
the absolute sound pressure by a factor of 4.
The dB level is thus reduced by half twice (2 x 3 = 6 dB). New dB reading = 96 - 6 = 90 dB.
Plan B: Reducing the absolute
sound pressure by 75% would result in a new absolute sound pressure of 25% (or
one-fourth) of the old absolute sound pressure.
Therefore Plan B, like Plan A, is also a reduction by a factor of 4 or a
6 dB reduction. New dB reading = 96 - 6
= 90 dB
The two plans are equally
effective in that each reduces the noise level to 90 dB. If both plans were employed at the same time,
each plan would reduce the absolute sound pressure by a factor of 4, resulting
in a 16-fold overall reduction. Note
that a 16-fold reduction is a halving of the sound pressure four times (24
= 16). Each time absolute sound pressure
is halved, sound level is reduced by 3 dB.
The sound level is thus reduced by 12 dB (4x3dB = 12dB). New dB reading = 96-12 = 84 dBA.
RESEARCH EXERCISES
10.28. A professional recommendation to this
employer should first establish whether the general asbestos standard, 29 CFR
1910.1001, applies. Subparagraphs (a)(2)
and (a)(3) of this standard exclude construction and ship repairing,
shipbuilding, and shipbreaking and if the employer is in these industries,
other applicable standards should be consulted.
It is assumed in this problem that since none of these special industry
categories were mentioned, the general standard applies. In subparagraph (f) - Methods of Compliance,
the standard for the most part permits either engineering controls or work
practice controls to be used to reduce the exposure of employees to acceptable
levels. However, the employer’s
attention should be directed to several provisions of subparagraph (f)(1) of
the standard that specify certain engineering controls and production
procedures WHETHER OR NOT ADMINISTRATIVE CONTROLS ARE USED ALSO. Certain asbestos operations REQUIRE local
exhaust ventilation, in accordance with 1910.1001(f)(1)(iv) and (v). Specifically, local exhaust ventilation is
required for the use of “hand-operated and power-operated tools which would
produce or release fibers of asbestos, such as, but not limited to, saws,
scorers, abrasive wheels, and drills.”
Such local exhaust ventilation is required to be “designed, constructed,
installed, and maintained in accordance with good practices such as those found
in the American National Standard Fundamentals Governing the Design and
Operation of Local Exhaust Systems, ANSI Z9.2-1979.” Another engineering control specified by the
standard (1910.1001(f)(1)(vi)) is wet methods “insofar as practicable” whenever
asbestos is “handled, mixed, applied, removed, cut, scored, or otherwise
worked” in order to prevent the emission of airborne fibers so as to expose
employees to levels in excess of the TWA and/or excursion limit specified by
the standard. Particular products and
operations require one or more ENGINEERING controls as specified by
1910.1001(f)(1)(viii). Specifically, the
removing of asbestos “from bags, cartons, or other containers in which they are
shipped” requires wetting, enclosure, or ventilation “so as to prevent
effectively the release of airborne fibers.”
Special engineering control precautions are specified for the use of
compressed air for removal of asbestos or materials containing asbestos
(1910.1001(f)(1)(ix)). Basically,
compressed air is prohibited for this purpose, unless a ventilation system is
properly engineered to effectively capture the dust cloud created by the
compressed air. Sanding
asbestos-containing floor material is prohibited by 1910.1001(f)(1)(x). Another
method must be engineered to replace the sanding operations. There are detailed requirements for brake and
clutch repair operations; these requirements are specified in Appendix F of the
standard. Often the employer uses
employee rotation as a work practice control to reduce employee exposure to maximum
acceptable time-weighted average exposure levels, but for asbestos operations,
employee rotation to achieve compliance is not an option. OSHA standard 1910.1001(f)(2)(iv) specifies
that “the employer shall not use employee rotation as a means of compliance
with the TWA and/or excursion limit.”
These are significant drawbacks to the administrative (work-practice)
control strategies, and management should be made aware of these drawbacks.
10.29. OSHA
standard 1910.1001(h)(3)(ii) expressly prohibits “the removal of asbestos from
protective clothing and equipment by blowing or shaking.”
10.30. The
Lead Industries Association was joined by the Battery Council International
along with the Occupational Safety and Health Administration in a voluntary
initiative to protect the health of lead workers. This initiative was announced on October 30,
1996 (USDL News Release 96-457):
“Representatives of 33 companies, the vast majority of members in the
two associations, have agreed to the program.
The companies have 20,000 workers in such industries as battery
manufacturing, lead smelting, lead chemicals, fabrication using lead, and
solder manufacturing.”
Two targets were identified, as
follows:
OSHA
Industries’
Spec Target Initiative
Trigger blood level for relocation
of 50 micrograms 40 micrograms
workers to an area in which lead
exposure is less than the 30
micrograms
per cubic meter action level
(per 100 grams of whole blood)
Blood level target for return to
work 40 micrograms 35 micrograms
(per 100 grams of whole blood)
Both of the above targets were
scheduled for a 5-year phase-in with the relocation target to decrease at the
rate of 2 micrograms per year and the return-to-work target to decrease at the
rate of 1 microgram per year until the 5-year targets are reached.
10.31. From the OSHA website, the general
industry industrial noise standard is found to be OSHA standard 1910.95. This
standard contains provisions for exposure to excessive noise plus provisions
for monitoring, hearing conservation programs, and personal protective
equipment. The NCM database shows that OSHA standard 29CFR1910.95 was cited
2265 times for the fiscal year, and that 1283 of these citations were
designated as in the “serious” category. Thus, the percentage of serious
violations is 1283/2265 = approximately 57%. The total dollar amount of the
penalties proposed for the alleged violations was $1,548,498, for an average
penalty per citation of approximately $684.
10.32. Using the keyword search capability of
the NCM database, searching on the term *exhaust
hood* returns a tabulation of 122 citations of various standards. Of these
122 citations, 116 were classified as “serious.” Thus, the serious citations
represented 116/122 = approximately 95% of the total.
10.33. Using the OSHA website, the relevant
provisions of the OSHA noise standard are listed along with the total number of
citations and the number of serious citations for Fiscal Year 2002, as
determined from the NCM database:
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Total
citations |
Serious
citations |
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Audiometric
testing |
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1910.95(g) |
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