RESPIRABLE OUST CONCENTRATION ug /m?

TIT. RESULTS AND DISCUSSION

A. Workplace Environmental Conditions

Packing

Table 2 and" igure B present the atmospheric concentrations of silica
dust where local exhaust ventilation systems have been installed as
the primary method of dust control. Both effective and partially
effective dust controls were observed at these plants. For example,
at all three plants, where main product flour (-200 to 325 mesh) is
packed on 4 spout St. Regis packers (Photo 1-3), dust exposures were
controlled to below the MSHA limit and above the NIOSH recommended
limit. Average respirable silica dust concentrations were
approximately 84 ug/m , Table 2.2. At two locations, however, where
packing and palletizing of fine product flour ( <38 um) were performed
intermittently, respirable silica dust concentrations averaged

451 g/m, Table 2.3. Additional improvement of these dust control
systems is necessary.

800, NTR
i 8 - Ventilation Only '
7doF- \ O- Ventilation with Water in Product
i E - Ventilation with Water Sprayed on Begs 7
1 Co - Ventilation with Water in Product and on Bags [0+ £]
BOO; ¢ H A - Ma Bagging
' BACKGROUNG ;
1 = - Gutdoors Upwind abl espicsble
soOr ‘ d- Dutdeore Douwnuind sense Silica
{2 LOCATIONS} 4 c - Indoors Packer Area Oust
4oO + g '
1 [3 LOCATIONS }
S00+ ' :
Bec a d cad :8OECad: Bad BadAHad
200} : 1 : t Ke
: TLV SILICA = 100 pg /m3 : A : id \
00 = A H
o Le oAA Mofo. (AA Ilaoiloo

Fine Product Siice Flour [<38 um} Main Praduct Silica Flour [> 38 pm]

Figure & QUST CONCENTRATION ar PACKERS


CLOSED HATCHES
EXHAUST VENTILATICN
HOOD

)

FLEXIBLE
EXHAUST DUCT

OPEN HATCHES

PARTITION;
A oo

|
3
‘
;
i AX *

ey KS
MILLING BUILDING 7 aS
LQ...

CFLEXIBLE FILLER HOSES

PLAN VIEW \

FLEXIBLE FILLER HOSE
— mr

EXHAUST VENTILATION
HOOD

CLOSED HATCHES Vee Flew
x : ——r.. mT Z| > id
AE — oreN

fis HATCHES

PRODUCT,

PARTITION’

CROSS SECTION A-A

Figure 0: Bulk Rail Hopper Car Loading

30


Dust levels at two fine poudey packing stations were high,
averaging about 515 yg/m? respirable dust and 350 ug/m>
respirable silica dust (Table 3.4 and 3.5 and Figure K).
Although exhaust ventilation flow rates were high, ranging

from 100 to 4800 fpm at the hood faces, dust control was
inetfective. This was probably caused by: uneven flow
patterns, created by cross drafts in the packer areas; exhaust
hoods located remotely from dust sources; and spills on
floors, which were not removed promptly or properly.

NJ AIR VELOCITY IN
Se FEET PER MINUTE, fpm

8 ‘eS
Bade

Ya
.
°.

Figure K: Ventilation at Fine Product Packing Areas

26


4. Other engineering controls

The effectiveness of other enginering control measures, involving
equipment, facilities, and operations, were evaluated
qualitatively.

a) Equipment modification

1)

4)

6)

Bag removal - An automatic bag ejector resulted in less
product spillage from the fill spouts and bag valves
(Photo 2). This device does not operate until the feed
valve shuts off, allowing adequate delay time between
valve shut-off and automatic kick off. This permits the
air in the bag to bleed off, thereby, reducing bag valve
leakage.

Nozzle design - Tapered sleeves and inflatable valve seals
improve the seal at the nozzle/bag interface. These must
be properly sized to fit the bag valve and must be
maintained in good working order.

Conveyor transfer points - Minimal drop distance for
filled bags from one conveyor to another reduces bag
leakage from the valve or loose seams (Photo 5). Also,
bag breakage will be reduced.

Fluid bed driers and extended stacks - Extended the stacks
on baghouses and other ventilation systems reduces
background dust concentrations. Replacing steam driers
with enclosed fluid bed driers also produces less dust.

Automatic shakeouts - Automatic shakeouts on a timed cycle
can improve the operation of the baghouses, further
reducing employee exposure.

The Ritten Electrostatic Fogger* (Photo 8), has also been
used to agglomerate airborne dust in high dust areas, such
as boxcar loading. The effectiveness of this device
should be evaluated.

b) Facilities modifications

is

Plastic curtains - Overlapping strips of transparent
plastic form a curtain to provide easy traffic flow and to
increase the effectiveness of the local exhaust control
system (Photo 17).

*Manufactured by the Ritten Corporation, Ltd., Ardmore, PA. 19003.

35


3) to identify gaps in existing contro] technology, which may be
resolved by appropriate research and development programs.

Control Technology Elements

Hazard control technology consists of four elements. Two of these are

equipment, process, and facilities oriented: engineering controls and
environmental monitoring; and two of these are worker oriented: good

work practices and the use of personal protective equipment.

II. STUDY PROTOCOL

A.

Evaluation Criteria

Tne Threshold Limit Value (TLV)* for respirable crystalline silica
(quartz), which is applicable in metal/non-metal mines and ys: is
contained in 30 CFR (Code of Federal Regulations) Part 57.(12) This

standard is determined by the free crystalline silica content of a
dust and is calculated by the following equation:

TLV = 10 milligrams per cubic meter of air
% respirable quartz + 2 (mg/m?)

For 100% respirable silica dust, this calculated TLV is approximately
equivalent to 0.1 mg/m3 or 100 micrograms per cubic meter (ug/m3)
of air.

NIOSH, in 1974; (13) recommended an Exposure Limit of 0.05 mg/m3

for all forms of respirable, crystalline silica, including quartz.
NIOSH reiterated this recommended standard of 0.05 mg/m? in its
Current ose Bul lepin (CIB) on "Silica Flour - Silicosis" in
1981, (14 Nelson, et al » in 1978 recommended that the
Threshold Limit Value (TLV) for silica flour dust be reduced to 0.05
mg/m3 of respirable dust. The MSHA TLV and the recommended NIOSH
Exposure Limit refer to daily (8 to 10 hours, time-weighted average)
exposures to employees. In this report, the MSHA TLV and the NIOSH
Exposure Limit are used as environmental criteria to evaluate the
effectiveness of the control techniques under investigation.

*Threshold Limit Values (TLV's) are adopted yearly by the American Conference
of Governmental Industrial Hygienists (ACGIH). They “refer to the airborne
concentration of substances and represent conditions which it is believed that
nearly all workers may be repeatedly exposed, day after day, without adverse
effect." In 1977, MSHA promulgated ye TLV for silica dust, which was
recommended by the ACGIH in 1976.(!2


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45


4. Preventive maintenance should be performed on a routine basis by
well-trained maintenance staff.

5. If incentive pay plans are used, they should be designed to

provide for effective and timely cleanup of spills and for the use
of good work practices.

Environmental and medical monitoring programs are essential. They
should include:

1. Environmental monitoring of potential dust sources; monitoring the
performance of ventilation and other control systems; and personal
monitoring procedures.

2. Periodic medical examinations, including serial pulmonary function
testing and chest x-rays to detect changes in physiological
conditions.

An effective respirator protection program should be instituted to
ensure proper fit, maintenance, and use of respirators.

Additional experimental research needs to be conducted in the
following areas:

1. Tne Gnisa ss of adding agglomerating agents, such as Deter
Micro Foam’, to flour products has not yet been resolved.

2. A portable environmental dust monitor, capable of quantitative and
qualitative analyses for silica, needs to be developed.

3. The relative effectiveness of wet sweeping, with emulsion
additives, versus vacuum cleaning has not yet been determined.

4. The effectiveness of The Ritten Electrostatic Fogger in agglomera-
ting atmospheric respirable dust needs to be evaluated.

5. Leakage from valves and seams of filled bags continues to be a

source of contamination. A stronger, leak-proof bag needs to be
developed.

43


17. Pritchard, J.A. "A Guide to Respiratory Protection." USDHHS, PHS, CDC,
National Institute for Occupational Safety and Health, June 1976, HEW
Publication No. (NIOSH) 76-189. p 137-148. Appendix B and F.

18. NIOSH Certified Equipment List as of June 1980. USDHHS, PHS, CDC,
National Institute for Occuptional Safety and Health. DHHS (NIOSH)
Publication No. 80-144.

49




Appendix B shows an effective respiratory protection program found at
one of the study facilities. At this plant, one full-time technician,
accountable to the plant manager, is responsible for the above men-
tioned respirator procedures. Also, two or three respirators are
assigned to each employee so that the worker always has at least one
properly maintained and fitted respirator available. One facility in
the plant area has been dedicated for respirator maintenance and
fitting. "High dust exposure" areas are designated for “mandatory
respirator use." Finally, all supervisors are responsible for
monitoring the proper use and operational condition of respirators.

IV. GENERAL OBSERVATIONS, CONCLUSIONS, AND RECOMMENDATIONS

A.

Control of. dust in all areas requires a combination of good engi-
neering controls such as the use of dust suppressant additives,
exhaust ventilation, and controlled bulk loading of products; good
work practices, including product handling and housekeeping pro-
cedures; effective environmental and medical monitoring programs; and
an effective respiratory protection program. As dust emissons from
point sources are reduced, it normally follows that the levels of
personal exposure to atmospheric dust are also reduced proportionately.

A firm commitment by management and workers to implement and use good
environmental control and occupational health programs is essential.
This commitment was demonstrated at the plants investigated.

Standard ventilation and housekeeping procedures, presently in use at
these plants, are capable of maintaining respirable silica dust
concentrations below the present TLV of 100 ug/m3 at the following
operations and areas: normal packing of main product silica flour;
conveyor transfer points; pallet loading of bags from conveyors (with
down draft floor grills); and bulk loading of railroad and truck
hopper cars, under local exhaust ventilation control. Major areas of
high dust exposure include hand loading of boxcars and trucks from
conveyors or fork trucks; and intermittent packing and palletizing of
fine silica flour.

Outside areas may contribute as much as one-third to one-half of the
in-house dust contamination problem. Ambient dust sources, which
normally contain approximately 20 to 30 percent silica, may be reduced
by resurfacing roads, planting vegetation, covering sand piles (with
sealants or shrouds), and wetting road surfaces with salt water.

Several experimental methods of dust control indicated that:

1. Injection of agglomerating agents, such as water or Deter Micro
Foam(R), into products was effective in reducing dust emissions
by an average of 60% in packing and bag handling areas, and in
bulk loading of silica sand and flour. It was less effective (23%
reduction) in manual loading of bags into boxcars.

41


Transfer of Bags Between Conveyors

4. Conveyor transfer point; minimum drop, clean bags

5. Conveyor transfer point excessive bag drop, broken bag,
incomplete spray capture, use of respirator

13


2. Agglomerating agents

In one plant, water (up to 1.5% by weight) was injected into
silica flour, at each filler spout during bag packing (Figure E).
The water causes fine dust particles to agglomerate, thereby
reducing the emission of dust during bag handling. A series of
dust evaluations were conducted under different control condi-
tions. Table 4, Run D (with water injection) indicated that
respirable silica dust concentrations were reduced by more than
60% at the packer station, from 96 ug/m to 39 g/m ,

(Figure B) and by approximately 85% at the bag handling areas,
from 345 ag/m3 to 53 g/m, (Figure C). At boxcar loading
operations, however, only 23% reduction in silica dust
concentration was achieved, from 1521 wg/m3 to 1164 ug/m3, by
water injection (Figure D). Thus, this technique showed excellent
potential for reduction of dust exposures around packing and bag
handling operations, if the product is acceptable with this water
content.

At a second plant the agglomerating agent, Deter Micro Foam(R)*
was being tested for its reduction of dust dispersion, after its
injection into sand. At the time of this study, Micro Foam(R)
was being added only to sand in its transfer through the sand
screening building. In this system, a mixture of compressed air
(approximately 99%), water (approximately 0.9%) and Micro

Foam (approximately 0.1%) was nebulized into a conveyor
stream of silica sand. Minute foam bubbles, between 100 and 200
am in diameter, were formed. These bubbles intercepted fine dust
particles and agglomerated them into larger, heavier, and
non-respirable particles. Although the effectiveness of this
material for silica flour dust suppression has not yet been
evaluated, it has shown to be effective in sand dust suppression.

Tests conducted by the company, indicate that, when added to sand,
it may reduce dust levels by as much as 67%, from 84 mg/m3 to 27
mg/m>, inside an enclosed hopper car during bulk loading

(Table 4).

Tables 5, 6 and 7 present the general findings of dust concentra-
tions at the three plants investigated. Table 8 presents the
chemical and size analyses of bulk air, product, and rafter
samples at one plant.

*Deter Micro Foam(R) 1010 is a registered product of the Deter Company,
Inc., East Hanover, N.J.

31




At a third plant, silica dust emissions from the packer
machines were controlled by an exhaust System involving two
sets of hoods, (Figure I and J, and Table 3.3). One set of
hoods, behind the Packer machine, moved air laterally away
from the operator toward the packer machine. The average air
velocity at the face of the Packer mach ine hoods was 324 fpm.
A second set of hoods, below the packer operator and adjacent
to the conveyor, moved air downward. The average air velocity
of this slot hood was 1650 fpm (Figure J). This system
resulted in an air pattern down and away from the operator's
breathing zone. Air samples were taken during periods of "no
Packing" and of "packing." During "no Packing" dust
concentrations averaged 220 ug/m3 respirable dust and

75 ug/m3 respirable silica dust (34% silica). During a
period of "packing," dust concentrations averaged 212 ug/m3
respirable dust and 112 ng/m3 respirable silica dust (53%
silica) (Table 7.2).

|___ LOADING DOCK A
EXH. VENT'N: BELT CONVEYOR
soo
o i SZ ll
5 oh/
g SSB 66 NG DECLINE SLIDE
ei
ail] Geeraust vewrivarion
i
FLOOR GRATING~’ A<—

CHAIN CONVEYOR

LOADING DOCK PLAN VIEW

X- SECTION
$_ PRODUCT ll

4 SPOUT

tha
EXHAUST VENTILATION PACKER UPPER DECK

EXHAUST.
OUST FROM VENTILATION
BAG HOUSE
DOCK OOCK

SUB-LEVEL

CONVEYOR

SECTION- A-A
Figure 1: Packing Area - Main Product
24


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16


RESPIRABLE OUST CONCENTRATION ug /m?

B00

700

600

soo

300

200

(00

T

Bag transfer between conveyors

Transfer of bags between conveyors may also be a major source of
atmospheric aust (Figure C). This source can be controlled as shown
in Table 2.5a. At one location (Photo 4) where transfer is automatic
and drop distance between conveyors is minimal, the average respirable
silica dust level was 65 ug/m3. At a second location, however,

where bags were manually assisted in transfer between conveyors

(Photo 5), respirable silica dust levels averaged 345 yg/m3.
Additional dust control is necessary at this dust emission source.

Pallet loading

Dust dispersion, during palletizing of bags from conveyors, is another
major source of dust (Figure C). This source can be reduced by a
combination of good engineering controls and good work practices.
These include proper bag handling to minimize bag breakage, and prompt
cleanup of spills through a down-draft grill (Photos 6 and 7).

Table 2.6a and b indicate that unequal dust emissions occur around the
pallet loading area. An average concentration of respirable silica
dust of 86 yig/m3 was measured on three sides (the upwind side} of

the conveyor, whereas the downwind concentration was 250 yg/m.

This may be caused by excessive draft from nearby open doors.

QUST CONTROLS
8 - Ventilation Onky
O - Ventilation with Water in Product
E - Ventiletian with Water Sprayed on Bags
C= Ventilstion with Water in Product “and on Bags [0+ €]
A - fo Bagging
BBCKGROUNO
3 - Outdoors Upwind Respir abl Respirable
d - Gutdoors Qawnuind nace {A Silica
e — Contamination Qust
(1 Location j
d Aad Bead
:
ba

TLV SILICA = 100 g/m?

nlln.. eaoliol

Af

'
‘
1
1
1
'
'
1
1
1
!

5 1
1
I
L
n
'
1
1
n
n
1
'

Conveyors [belts, chains, springs] Palle tizing

Figure C: QUST CONCENTRATION ror BAG SANOLING

12


210 Z
AIR VELOCITY IN Ve

FEET PER MINUTE ,fpm
& 7230! x $
of y 400 we
ee af a <
i N
* cmd v E W
¢' h
és
w 10, / Vir 3 “a
Jf A00 ‘
28 ws AQ
tag

/ 30 || 7
Sly ff °

BELT

Yr 270 CONVEYOR

Vi90

Figure J: Ventilation at Main Product Packing Area

)

Since the silica content of the airborne dust was relatively
low during both operating conditions, probably the major
source of dust was background contamination.


Uo

Study plan

Three silica flour plants, one medium and two large, were chosen
for in-depth evaluation. Management at each of these plants has
demonstrated a commitment to improved worker health through
environmental and medical monitoring, hazard evaluation, and
environmental control programs.

Furthermore, recent MSHA environmental data have indicated that
dust exposures at these plants have been reduced by the
development and implementation of good dust control procedures.
Innovative dust control techniques were also being installed and
evaluated at these plants.

The effectiveness of standard control methods, in use at several

operations; was evaluated quantitatively. These operations
included:

a) packing - main product, 74 to 43 um (minus 200 - 325 mesh) and
fine product, 5 to 34 um; silica flour is packed into 3-ply,
50 and 100 pound bags, using 4-spout, 2-spout, and 1-spout
packer systems.

b) conveying - filled bags are transported via conveyor belts
from packing stations to pallet or truck/boxcar loading
stations.

c) bag loading - filled bags are loaded on pallets or directly
into boxcars or trucks (with or without pallets).

d) bulk loading - bulk flour is loaded into closed railroad or
truck hopper cars, through ducts, using exhaust ventilation
for dust control.

In addition, two experimental dust control procedures were
evaluated. These were:

a) injection of agglomerating agents - at one plant, up to 1.5%
by weight of water was added to silica flour during packing in
100 pound bags. Ata Second plant, the agglomerating
agent,(15) Deter Micro Foam(R) was being tested for dust
suppression in the transport of sand. Micro Foam(R) is now
being tested for suppression of silica flour dust.

b) application of water sprays - at one plant, water is sprayed
on filled bags of silica flour, through sonic water jets, at
several strategic locations along its conveyance from packer
to pallet loading. The water is used to agglomerate and to
remove dust accumulated on the bags' outer surfaces.


Appendix B
RESPIRATORY PROTECTION PROGRAM

The basic purpose of the respiratory protection program is to provide the
worker with a healthful environment. The primary method of protecting the
worker against respiratory hazards is engineering controls that either
eliminate or reduce the dust hazard. However, when situations occur where
engineering or administrative controls are impractical or ineftective,
personal respiratory protection must be worn.
In order to have adequate protection against respiratory hazards by the use of

respirators, a comprehensive program detailing the use of respirators must be
carried out.

All employees at the plant will be turnished with two respirators and the
following shall govern their uses:

Respirators

Mine Safety Appliance 'Dustfoe 66" or "Dustfoe 77'' respirators will be
provided.

Training

Respirator training shall be provided as mandated under 30 CFR 48.24(2) -
"Self Rescue and Respiratory Devices" - MSHA Training.

Maintenance

1) Each employee who has used a respirator during the shift shall deposit it
in the assigned container.

2) Each respirator shall be collected daily.

3) Each respirator shall be disassembled, inspected, cleaned, dried, repaired
as required, and enclosed in an individual plastic bag.

4) Each cleaned respirator shall be returned to its assigned bin by 3:00 p.m.
each day.

5) The respirators shall be sanitized with "MSA Cleaner and Sanitizer."
6) A daily log shall be kept of each person's respirator use.
Supervision

All supervisors shall routinely monitor the use and condition of the
respirators.

Administration

One qualified person shall be responsible for the program and shall be
accountable to the plant manager.

51 Ye 0. 8. GOVERNMENT PRINTING OPFICE:1984~-759-103/10908


ACKNOWLE DGEME NT

We gratefully acknowledge the cooperation and assistance of the management and
workers at the plants participating in the field studies. Their willingness
to contribute their experience and knowledge in the areas of silica processing
and hazard control made this study possible. In particular, we wish to thank
Mr. Charles Hawkins of the National Industrial Sand Association (NISA) and Mr.
Arnold Alekna (deceased) and members of the NISA Committee who have produced
excellent documents relating to the improvement of Occupat} nal Health and
Dust Control Programs in the silica production industry 2" Dr. Aurel
Goodwin, of the Mine Safety and Health Administration (MSHA) provided us with
valuable environmental and production data.

We also are indebted to Drs. Charles Geraci, John Palassis, Jonn Holtz and

other members of the Measurement Support Branch, NIOSH and the staff of the
Utah Biomedical Testing Laboratory (UBTL) for their analytical support. I1lu-

strations were prepared by Mr. August Lauman. The manuscripts were patiently
and ably typed by Ms. Myra D. Brooks.

ix


P30
seo

4 No} “4§--p--- == -----80

gee - et
vgyeee == $80
> AIR VELOCITY ONE FOOT “<<.
FROM FACE AND AT FACE “hg

Feet per minute (fpm) '— & =

Figure F: Ventilation measurements - Main Product Packer

At a second packer station, (Figure G@ and Table 3.2), dust
levels were 145 yg/m3 respirable dust and 63 ug/m3

respirable silica dust. Effective dust control was developed
by a "push-pull" ventilation system. This included an exhaust
hood behind the packer machine; a second system below the
conveyor; and an over head area fan behind the packer
operator. The fan provided a curtain of clean air past the
operator's breathing zone. The average air velocity at the
face of the packer machine hood was 92 fpm (Figure H). The
silica content of the airborne dust in this area was low,
approximately 43%, and the flour product being packed was
essentially pure silica. Thus, a major portion of the dust
load in this area probably evolved from sources other than the
packer, i.e., background dust.

22


B. Effectiveness of Engineering Controls

1.

Local Exhaust Ventilation Systems

Table 3 describes and summarizes the ventilation control systems
at the various operations.

a) Bag packing (Photos 1, 2, 3)

Local exhaust ventilation systems were capable of maintaining
silica dust concentrations close to or below the MSHA TLV of
100 ug/m5, when main product silica tlour was being packed.
However, they were not capable of reducing dust levels to the
NIOSH recommended level of 50 ug/m>. At one plant (Figure E
and Table 3.1), the packer exhaust system moved air laterally,
from the packer operator toward the packer machine. Simulta-
neously, the conveyor belt exhaust system moved air from the
operator toward an exhaust slot beneath and behind the
operator in opposition to the air flow of the packer exhaust
system. This appeared to create a "null zone" of air movement
in the vicinity of the packer operator. The average air
velocity at the tace of the packer machine hood was low, 45
feet per minute (fpm), (Figure F); the average velocity at the
face of the hood behind the packer operator's seat was

1000 fpm. Dust levels were controlled to 103 yg/m3
respirable dust and 96 ng/m> respirable silica dust.

a

orenaTons
‘SEAT

ttle

fA fp |

SPOUT AND
‘WTER IRIECTION

eal

PACKER AREA

7 Bimaust vewrnation —

t |i nyt
UE
¢ hal
S :

“FLOOR

CROSS SECTION A-A

Figure E: Packer - Ventilation and Water Controls

19


Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

TABLES

Page
Equivalence of Screen Mesh to Particle Size -
U.S. Sieve and Tyler Sieve SerieS.......e.cceeceeeeee 5

Respirable Silica Dust Concentrations - at Three
Flour Mills (Ventilation Control only)...........000. 11

Description and Effectiveness of Ventilation
COTIUEPO I sSiSEEIIS0 0000000000000000000000009 00000060000 20

Effect of Addition of Deter Micro Foam(R) to

San Gu PVOGUGES feleletelfelelelelsteleletlastelictelerstel= pooomnododonobo 32
Respirable Atmospheric Dust Concentrations During

Four Experimental Runs..... o00D00 0000000 ogo00e00000 90 44

Respirable Atmospheric Dust Concentrations During
Two Experimental Runs...... 9000000000000 0009000 909090 45

Respirable Atmospheric Dust Concentrations During
Two Experimental RUNS..... cece cee neces e cee eccceeeens 46

Chemical and Size Analyses of Bulk Air, Product,
and Rafter SampleS.......eee sees eee e eens gococcccacn 00 47

vi


CONTENTS

Page

(NYSUES E00 000000000000000000 0000900000000 D0000000000000000q000 Vii
Acknowledgement ix
INTRODUCTION... cccceccccccvcccccsccscccccsvccccccnscccccscccesscserens 1
Bo EERO oo co 000000 00000000000000000000000000000000000000000 1

B. Purpose of Study 1

C. Control Technology Elements 3

Wits  SuULk? GRWUC EL coa5cnonc0c000a9G0e0D000G000000DG00000000000000000 3
fo (NUE GPUs 000000000 00000000000n00000000090 000000079 3

B. Industry Description.. 4

J. Process description . 4

fo DIES GERUIlooo000000000000000a0 0000000000000 0000anDEDR00 6

C. Scope of Study gcgco00000000090000DaDG00000 6

1. Study plan...... 00 . 7

2. Investigation procedures.....cccccccccccccccccsecesessccs 8

Wolo KESILUS A) SEUSS Oll5000000000000000000000000000000000000c0000 9
A. Workplace Environmental Conditions. .......eeeececcesccceeeees 9

B. Effectiveness of Engineering Controls....eseeceeeeeccsscsceee 19

1. Local exhaust ventilation systems 9 19

2. Agglomerating agents.........+.- o 31

3. Cleaning of bag surfaces.. . 33

4. Other engineering CONtrolS....sececeeceeceeececccecreeeee 35

C. Control Monitoring.......cscseeeeeeseecees 0 38

1. Environmental monitoring . 38

2. Medical Monitoring. .......cccccccccccccccccccccseveceeens 39

Do Ubrls reetE88000000000 0000000 0000000000000 D000N000000c000n000 39

E. Respiratory Protection ProgramsS.......sceeecececvcccsccseveee 40

IV. GENERAL OBSERVATIONS, CONCLUSIONS AND RECOMMENDATIONS............ 4]
Wo GieERERTS.0000000000000000000000000000a00000000G00000000000000000 48
Wo A HENWEESc0000000000000000000000000000000000 O00000000000cD0000000 50
A. Description of Air Sampling and Analytical Equipment......... 50

B. Respiratory Protection Program.......cseceeeseccecccseenscees 51


(n

Investigation procedures

a)

b)

Environmental dust measurements

Atmospheric dust concentrations were measured to evaluate the
effectiveness of dust control procedures. Measurements were
taken at potential sources of dust contamination and at
general work areas. Additional atmospheric measurements were
made upwind and downwind of the plants. Upwind samples were
collected to estimate the contribution of background dust,
unrelated to plant operations. Downwind samples were
collected to estimate the contribution of in-plant dust
sources to the ambient environment. Bulk samples (rafter,
product and high volume air samples) were collected to
determine the chemical composition and particle size
distribution of product and airborne dust. Four types of dust
samples were collected and analyzed.

1) Integrated air samples (several hours in duration) were
collected with MSA Gravimetric Dust Samplers with attached
cyclone separators. They were analyzed quantitatively (by
weight) for "respirable dust" and "respirable silica dust".

2) Short-term, direct reading atmospheric measurements of
"respirable dust" (several minutes in duration) were made
with the TSI Respirable Aerosol Mass Monitor, Model 3500,
to identify potential dust emission sources.

3) Air samples were collected with the Del High Volume
Electrostatic Precipitator (ESP) sampler with an attached
cyclone separator. The purpose of this sampler was to
collect sufficiently large airborne samples for accurate
identification of the airborne dust, both in silica
content and in particle size distribution.

4) Bulk rafter and product samples were also collected and
analyzed for silica content and particle size
distribution. These results were compared with ESP
sampler results.

All samples were analyzed either at UBTL or at NIOSH's
Measurements Support Branch Laboratory. Descriptions of
sampling and analytical procedures and methods are presented
in Appendix A.

Ventilation control measurements

Ventilation and air flow pattern measurements were evaluated
to determine the effectiveness of the local exhaust
ventilation systems. Velocity measurements were made with a
Kurz Air Velocity meter (Model 441) and air flow patterns were
evaluated with Gastec Smoke Tester tubes.


10.
1.
12.

13.

14.
15.
16.
7.
18.
19.

PHOTOGRAPHS

Page
Packing of 4-spout packer; water spray, nozzles
AL FITI-SPOUTS. co eerccccrccccccecsccescreccsccccnccsessvacece 10
Packing at 4-spout packer, automatic bag ejector;
use of respirator, down-draft grill.....ececceeeecceeseeeenes 10
Packing at 4-spout packer; 2 exhaust systems; use
of respirator.........00. Bonbon 00d00000eb0 UG000b0G0005 10
Conveyor transfer point; minimum drop; clean bags............ 13
Conveyor transfer point excessive bag drop; broken
bag; incomplete spray capture; use of respirator...........06 13
Exhaust floor grill; use of respirators.......secccccsescccee 14

Down draft floor grill; dry sweeping of spills; broken
bags at dust source.......

O0000G0G000D000000000000 14

Boxcar before bag loading; Ritten Electrostatic Fogger....... 16

Stacking bags in boxcars; no pallet; dirt on floor and
bags; use of respirator. ....seeeeeeees

Stacking bags in truck on pallets; use of respirator......... 16
Bulk loading open truck with sand; men standing by........... 7

Bulk loading closed hopper truck with exhaust;
dust well CONTrOLTEd... eee ee cee cece cece teen eee eecesenneeee 7

Bulk loading closed railroad hopper car with exhaust;
Fill-spouts and exhaust......ceseeseseveeee

Bulk loading closed railroad hopper car with exhaust......... 18

Spray nozzles (above and below) wash bags............ 34

Spray inside conveyor housing agglomerating dust............. 34
Use of plastic curtains to reduce cross-draftsS......eeseeeeee 37

Wet washing Of fl00r.....eeeeeeeeeeeee

p00000000000000000000 37

Plastic covering on loaded pallets, during storage........... 37

viii


Loading of Bags on Pallets

6. Exaust floor grill; use of respirators

7. Down draft floor grill; dry sweeping of spills; broken bags
at dust source

14


NiGSh

RESEARCH REPORT

A
Health Hazard Control
Technology Assessment

of the Silica Flour
Milling Industry

sae te

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service

Centers for Disease Control

National Institute for Occupational Safety and Health


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JTorjU0) SaTITTToeRTMZ pue Supdesyesnoy

37


ilo

A.

B.

INTRODUCTION

Background

Silica flour is produced by the crushing and milling of quartz sand or
quartzite rock. It is commonly used in abrasive cleaners, autoclaved
concrete blocks, foundries using lost wax investment casting, paints,
and as inert fillers.(3) Silica flour consists of essentially pure
crystalline silicon dioxide (quartz). Studies of the respirable dust
fraction of silica flour show that over 98% (by weight) of all the
particles are less than five micrometers in size, with a median
particle diameter even smaller.(4,5,6) Thus, most of the silica
flour dust is readily inhaled and retained in the lower portions of
the respiratory tract. Silica flour has been implicated as a
causative agent of a rapidly developing pneumoconiosis, qa} le4 “acute
silicosis" or "galloping silicosis." In 1956, Stokinger 7)
described cases of silicosis in the scouring powder manufacturing
industry, which developed after exposure to silica flour as short as
20 months. Recent NIOSH Health Hazard Evaluation/Epidemiology studies
were conducted at two flour mills in tAlanggse which have unique
deposits of micro-crystalline quartz. (8,9, These studies have
shown that exposures to silica flour dust can cause simple
pneumoconiosis to develop in periods as short as one to two years.
Progressive massive fibrosis can also develop, in periods as short as
two to two and one-half years of high exposures to silica dust.

According to MSHA data(11), 28 active silica plants employing
approximately 1400 workers, product silica sand. Some of these plants
produce both silica flour and whole grain sand. The number of em-
ployees per plant ranges from 4 to about 200. Fourteen (small) plants
employ from 4 to 30; eleven (medium) plants employ from 31 to 100; and
three (large) plants employ from 101 to 200 employees. Most of the
plants are located east of the Mississippi River while a few plants
are located as far west as Texas, Oklahoma and Kansas (Figure A.).

Purpose of Study

Because of the potential health hazard of exposure to this material,
NIOSH conducted a Health Hazard Control Technology Assessment (CTA) of
silica flour milling. This study was initiated at the request of MSHA
and conducted in cooperation with NISA and the Bureau of Mines (BOM).
The purpose of this study is to evaluate the effectiveness of the
health hazard control procedures, which are presently being used and
being developed for the bagging, handling, and shipping of silica
flour. The spécific objectives are:

1) to evaluate the effectiveness of existing control technology
procedures in silica flour milling operations.

2) to evaluate several new and innovative control strategies, which
are, at present, experimental, and




Appendix A.

Description of Air Sampling and Analytical Equipment

MSA Gravimetric Dust Sampler, manufactured by Mine Safety Appliances,
Inc. This sampling system consists of a 10 mm plastic cyclone separator
to remove "non-respirable" dust; a three-piece plastic filter holder
cassette, containing a 37 mm PVC filter, No. M5, manufactured by
Millipore Corporation or a FWS-B8 filter, manufactured by Mine Safety
Appliances, Inc.; and an MSA portable, battery powered pump, Model G.
This sampler is operated at 1.7 liters per minute, which is the standard

flow rate for collecting (respirable) silica and total dust samples.

Del High Volume Electrostatic Precipitator Sampler, Model ESP-100A, manu-

factured by Del Electronic Corp. This sampler, with respirable cyclone
separation, operates at 17 cubic feet per minute.

TSI Respirable Aerosol Mass Monitor, Model 3500, manufactured by Thermo-
Systems, Inc. This instrument permits direct measurement of dust
concentrations, at either two-minute or 24-second intervals. It
collects particles from 0.01 to 10 um in diameter. In a one-minute
sampling time it will measure mass concentrations in the range of 100
ug/m? + 10 accuracy.

Crystalline silica was analyzed witn a Phillips automated powder diffrac-

tometer, Model ADP-3501, with the "limit of detection" of 18 ug per
sample. Total dust weights were measured on a Perkin-Elmer Electro-

balance, Model AD-2, with a "limit of detection" of 10 ug per sample.
All samples were desiccated for 48 hours to obtain constant weight.

50


3. Cleaning ot bag surfaces

a) Water spray

At one plant, water was sprayed on filled bags with Sonic(R)
sprayers* at three strategic locations between the packing
and palletizing operations. These locations are: 1) at the
fill spouts - directly on the top of filled bags (Photo 1 and
Figure E); 2) at the transfer point between a horizontal
conveyor and a declining conveyor (upper level) - to the top
and bottom of each bag (Photos 15 and 16 and Figure L); and 3)
at the transfer conveyor (lower level) - on both sides of bags
(Photo 4, and Figure L). The spray patterns were overlapped
so that all exterior surfaces were thoroughly washed to
agglomerate and remove spilled product. Table 4, Ryn E (spray
on bags) indicates thdt respirable silica dust concentrations
were reduced by approximately 50% at the packer station, from
96 ng/m> to <44 ug/m> (Figure B); by approximately 75% at

‘the bag handling areas (from 345 yg/m> to 90 ug/m

(Figure C); and by 87% at the boxcar loading operations, from
1521 yg;m> to 204 ng/m> (Figure D). This technique also
indicated potential for reduction of dust dispersion during

packing, transport, palletizing and boxcar loading of bagged
silica flour.

When water is injected into product and sprayed onto bags
simultaneously (Table 4, Run C), 62% to 81% reductions in
silica dust concentrations can be achieved in all areas of bag
handling. Even with optimum dust control, however, respirable
silica dust levels during boxcar loading continues to be
hazardous, on the order of 317 wg/m> (Figure D).

b) Air cleaning

Bags may also be cleaned of residual dust by the use of air
jets located along their transport on conveyors. This

f procedure was not observed during this study. In the design
of such a system, exhaust ventilation inside a conveyor
enclosure must be sufficient to capture all of the jet air,
and to provide a control velocity into all openings of the
enclosure on the order of 150-200 fpm.

*Manufactured by the Sonic Development Company, Upper Saddle River, New
Jersey, 07458. ,

33


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reduces dispersion of residual dust on bag surfaces and
‘improves the weatherability of pallet loads in open trucks
and boxcars.

4) Wet slurry transfer - Replacement of covered conveyor
belts with a pipeline to remove the ore as a wet slurry
eliminates a source of background dust.

C. Control Monitoring

lo

Environmental monitor ing

Environmental monitoring procedures were also evaluated
qualitatively at these three plants.

Environmental monitoring is conducted for at least four purposes:
ventilation control evaluations; contaminant source identifica-
tion; work area monitoring; and personal exposure monitoring. The
first three monitoring procedures were performed in this study.

a) Ventilation control monitoring was conducted to quantify air
velocities and to define airflow patterns at specific work
areas. Since ventilation control constitutes a primary
control technique at silica flour mills, a routine, .periodic
ventilation monitoring program is valuable. Vane or hot wire
type direct reading velometers are useful in measuring air
velocities. They must be capable of measuring both low flow
velocities (10 to 500 fpm) and also high flow velocities (1000
to 6000 fpm). Weekly or biweekly measurements of hood
velocities, duct static pressures, differential pressures
across air filters, and visual inspection of integrity of
equipment are necessary to assure proper ventilation system
performance. Airflow patterns may be evaluated effectively
with ventilation smoke tubes.

b) Contaminant source monitoring was conducted to locate and
quantitify the magnitude of sources of airborne dust and to
measure the effectiveness of control systems. Direct reading
dust monitors, such as the GCA Respirable Dust Monitor and the
TSI Respirable Aerosol Mass Monitor were used in this study.
They measure peak dust concentrations over a short period of
time (seconds to minutes) thus, describing dust concentration
patterns. However, they are unable to differentiate between
solid particulates (mineral dusts) and liquid particulates
(water spray mists). This was a particular problem, where
sonic water sprays were used for dust control. Furthermore,
these instruments do not differentiate between silica dust and
non-silica mineral dusts.

In the plants investigated, outside (ambient) airborne dust
contained approximately 30 to 40 percent silica, whereas,
flour products were essentially pure (994%) silica. There-
fore, the composition of a dust cloud may identify its

38


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20


FIGURES

Location of Silica Flour Plants.......ccecececee eee ceeceeeaee

Dust Concentration at Packers.......ececeee cece cece eeeceeeere

Dust Concentration of Bag Handling......csecsesecsssccecceeee

Dust Concentration at Loading......scceeeeeeseccccceecesceees

Packer Ventilation and Water

CoM con0000000000000000000000

Ventilation Measurements at Packer.......esesceccccesecencees

Packing Area - Main Product.

Ventilation at Main Product Packing Area.......eececeececceee

Packing Area - Main Product.

Ventilation at Main Product Packing Area......ccessceeeeeeeee

Ventilation at Fine Product Packer Areas............eeeee 0000

Transfer Points - Ventilation and Water Sprays............00.

Ventilation at Pallet Loading Area......sceeeececccenceceeees

Bulk Truck Loading..........

Bulk Rail Hopper Car Loading

15
19
22
23
23
24
2
26
27
28
29
30


Respirable Silica Dust Concentration at Three

Table 2.

Flour Mills (Ventilation Control only)

railroad car, semi-
automatic

Respirable éverage éverage
silica dust concentra~ silica Type
Operation/Location concentrations tion content | Sample
ug/m g/m %
ft. Background
(3 plants)
a) Upwind of mills <1l, <13, <13, <16, <19 32 area
<25, 34
b) Downwind of mills <13, <13, <l6, 35, <23 64
c) Between buildings 38, 41, 46, SL 46 75
d) Truck loading dock 122 122 49
2. Packing-main product 96, <69, 61, 112 84 56 work
flour on 4~spout area
packers (3 locations)
B. Packing and palleti- 199, 451, 704 451 76 source
zing fine product
(2 locations)
%. Conveyor transport of 165 165 100 source
bags (1 location)
5. Transfer between
conveyors (2 locat-
ions)
a) Automatic transfer 64, 66 65 68 source
b) Manually assisted 247, 332, 456 345 87
transfer
6. Bag handling
a) Pallet loading from] 59, 63, 68, 84, 86 40 source
conveyor (upwind) 105, 139
b) Pallot loading from| 244, 256 250 67 source
conveyor (downwind)
c) Boxcar loading 1417, 1625 1521 80 work
from conveyor area
d) Truck loading 264 264 80 work
from conveyor area
7. Bulk loding of hopper 34, 34, 172 80 94 source

ng/m> - micrograms per cubic meter

< - less than

11



10.

i.

12.

13.

14.

15.

16.

REFERENCES

Occupational Health Program for Exposure to Free Crystalline Silica.
National Industrial Sand Association. Silver Spring, MD, 20910, 1977.

Guidance and Solutions to Reducing Respirable Dust Levels in the Bagging
of Whole Grain Silica Products. National Industrial Sand Association.
Silver Spring, MD 20910, 1977.

Nelson, H.M., G.S. Rajhans, S. Morton, and J.R. Brown. Silica Flour
Exposures in Ontario. AIHAd(39), Apr. 1978.

Watt, A.R. Private Communication. Indusmin Ltd., Midland, Ontario,
Canada, 1975.

Product Information Sneet. Tammes Industry, Chicago, IL, 1975.
Product Information Sheet. Ottawa Silica Co., Ittawa, IL, 1975.

Stockinger, H.E. Toxicologic Aspects of Occupational Hazards, Annual
Review of Medicine. Vol. 7, 1956. ref(17)Desolle, H., S. Tara, V.
Delplace, and A. Carigneaux. Arch. maladies profess. med. Trovailet,
Securite' sociale, 14, 279-83, 1953.

Morring, K.L., and D.E. Banks. Hazard Evaluation and Technical
Assistance Report. No. 79, 103-108, Illinois Minerals Company, U.S.
Dept. of HEW, PHS, CDC, National Institute for Occupational Safety and
Health (NIOSH), Cincinnati, Ohio, 45226, 1979.

Morring, K.L., and D.E. Banks. Hazard Evaluation and Technical
Assistance Report. No. 79, 103-108, Illinois Minerals Company, U.S.
Dept. of HEW, PHS, CDC, National Institute for Occupational Safety and
Health (NIOSH), Cincinnati, Ohio, 45226, 1979.

Banks, D.E., K.L. Morring, and B.A. Boehlecke. Summary Report...Silicos
in the 1980's. AIHAJ, 42, 77-79, 1981.

Unpublished data from Mine Safety and Health Administration, 1980.

Regulations and Standards Applicable to Metal and Non-metal Mining and
Milling Operations. 30CFRPart 57.5-1(a), Completed by U.S. DOL, January
1, 1980.

National Institute for Occupational Safety and Health. Criteria for a
Recommended Standard....Occupational Exposure to Crystalline Silica.
DHEW(NIOSH) Publication No. 75-120, 1974.

NIOSH Current Intelligence Bulletin #36. Silica Flour: Silicosis, June
30, 1981.

Cole, dr., H.W. "Microfoam for the Control of Source and Fugitive Dust
Emissions." Deter Company, Inc.

Chemical Engineers' Handbook - 3rd Edition, Ed. J.H. Perry, P. 963, 1950.

48


DEPARTMENT OF HEALTH AND HUMAN SERVICES

PUBLIC HEALTH SERVICE
CENTERS FOR DISEASE CONTROL 2
NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH
‘ROBERT A. TAFT LABORATORIES. US.MAIL
Bass

4676 COLUMBIA PARKWAY, CINCINNATI, OHIO 45226

Special Fourth Class -Book

OFFICIAL BUSINESS POSTAGE AND FEES PAID
PENALTY. FOR PRIVATE USE. $300 U.S. DEPARTMENT OF HHS
HHS 396

Redistribution using indicia is illegal. DHHS (NIOSH) Publication No. 84-110


c) Pallet loading

At one plant, filled bags are transported on an enclosed chain
convéyor to a pallet loading area (Photos 6 and 7 and

Figure M). A ventilation hood, enclosing the conveyor,
exhausted air laterally at an average velocity of 325 fpm.
Simultaneously, a down draft floor grill (7 1/2 ft. by 3 1/2
ft.) moved air downward at approximately 125 fpm. The average
dust concentration at this location was 225 ug/m3, respir-
able dust and 128 ug/m3 respirable silica dust Table 3.6).
However, downwind of the conveyor, two samples averaged 375
uug/m3 respirable dust and 250 ug/m3 respirable silica dust
(Table 6.1B.2), while upwind dust levels, average of three
remaining samples, were 217 ug/ms respirable dust and 87

yg/m? respirable silica dust. These concentrations indicate
that a significant portion of the dust was background. Bag
leakage and dry sweeping clean-up may also have been major
sources of atmospheric dust. Visual observations indicate
that an additional dust source may have been from open bulk
loading of sand into open trucks along the east side of the
builaing (Photo 11).

aq
S)
ea &
No ee?
oo
300
325
350
FLOOR a.
GRATE, of ries: ~\
fl Be 5
a i
ito caw AIR VELOCITY IN
S Stt FEET PER MINUTE, fpm
SN
B50 as
cs ‘A
t _
4 r4
~“s

AT FACE OF CONVEYOR DISCHARGE AND FLOOR GRATE

Freure M. VENTILATION AT PALLET LOADING AREA

28


d) Bulk loading

At one plant, closed hopper trucks and hopper railroad cars
were loaded with silica flour and sand under the control of
local exhaust ventilation (Photos 12 through 14, and Figures N
and 0). At the same plant, open trucks were being bulk loaded
with silica sand (Photo 11). Photos 11 and 12 show the
difference in dust dispersion under controlled and
uncontrolled conditions. Ouring controlled loading of a
closed railroad hopper car, atmosphere dust concentrations
averaged about 91 ug/m3 respirable dust and 80 aig/m3
respirable silica dust. At the same time, background (upwind)
dust levels were 74 uug/m3 respirable dust and < 3] ug/m3
respirable silica dust (Tables 6.4 and 6.5) Two 10-inch
filler hoses were positioned in two open hatches. A 30-inch
exhaust duct was positioned in a third hatch, while the 4th
hatch remained closed (Photos 13 and 14). During filling, an
average inward flow velocity of 230 fpm, at the filler hatch
(Figure 0), provided excellent emission dust control.

PRODUCT FILLER HOSE. it EXHAUST VENTILATION HOSE

CLOSED HOPPER TRUCK (FLOUR) LOADING

PRODUCT FILLER PIPE
bust
CEA tsa)
GiLe es || LYG

{|
WW
Za

OPEN TRUCK {WHOLE GRAIN SAND) LOADING

Figure N: Bulk Truck Loading
29


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*g alqey

44



Bulk Loading in Trucks

11. Bulk loading closed hopper truck with exhaust; dust well controlled

12. Bulk loading open truck with sand; men standing by

17

wha


Table 8. Chemical and Size Analysis* of
Bulk Air, Product, and Rafter Samples

Silica Particle Size (um)
Type Sample Location/Source Content Mass Median Aerodynamic**
% Diameter Diameter
1. Bulk Air Behind Packer
(Electrostatic | Upper level % 77 3.0 5.0
Precipitator
2. Bulk Product Flint Silica %100 14.9 24.3
Flour #325
3. Bulk Product Flint Silica %100 13.8 22.5
Flour #324
4. Rafter Pebble Mill % 100 19.4 31.7
5. Rafter South Side of % 100 7.6 12.3
Packer
Level with Packer
6. Rafter Main Floor Level,
East Siae Behind * 100 17.4 28.4
Packer Machine
7. Rafter West Walls Behind
Packer, at Packer | %100 29.8 48.6
Level

*Size Analysis by electron microscope at 400X magnification
**Aerodynamic diameter and mass median diameter calculated assuming density
of 2.66 g/cc
® Approximately
um_ Micrometer

47



ABSTRACT

A Health Hazard Control Technology Assessment of the silica flour milling
industry was conducted by the National Institute for Occupational Safety and
Health. Three silica flour mills were evaluated in depth. The primary
operations investigated were bag packing, conveyor transter of bags,
palletizing, loading of bags in boxcars and trucks, and bulk loading of hopper
cars and trucks. Several innovative dust control procedures were found to be
effective. These included: 1, the injection of agglomerating agents such as
water and Deter Micro Foam(R) into products; 2) water spraying of outer
surfaces of product-f1lled bags during conveyance; and 3) bulk loading of
silica flour into enclosed hopper trucks and railroad hopper cars under local
exhaust ventilation control. Plant personnel have estimated that half of the
environmental silica dust problems may be effectively controlled by good work
practices and effective housekeeping procedures.

iii


c)

2)

3)

5)

6)

Centralized bulk loading - This permits more effective
dust control with local exhaust ventilation.

Outside environmental control, i.e., surface modification,
paving, revegetation, and stock pile Covering - Paving of
roads and parking spaces and the use of brine or water
containing a surfactant to wet dirt roads help to reduce
background dust levels. Revegetation jis used as wind
screens and helps to hold surface soil. in place. Covering
of stock piles with shrouds or spraying with water reduces
dust from this source.

*
Sealed buildings - Sealing buildings and recirculating
plant air through bag collectors may reduce the
infiltration of background contamination. Placing the bag
filling operation(s) in sealed rooms with a filtered air
supply is also effective.

Floor grills - A floor clean-up grill at a conveyor
discharge and at pallet loading area(s) reduces dust
dispersion caused by bag breakage or spillage (Photos 6
and 7).

Control room air filtration - If mill operators spend a
significant part of the work shift in a control room,
tneir average daily dust exposure may be reduced by
introducing filtered air into the room. The volume of
filtered air introduced to a control room must be
sufficient to maintain a positive pressure in the room
when doors or windows are opened.

Process/operation modification

1)

2)

3)

Vacuuin cleaning and wet sweeping versus dry sweeping -
Both vacuum cleaning and wet sweeping are superior to dry
sweeping. Walls and floors should be washed to remove
accumulated dust and to flush spillage before it can
become airborne (Photo 18). The use of kerosene emulsions
helps to reduce dust dispersion by providing a more
persistent surface coating than water alone.

Bulk loading versus bag packing - Bulk loading with
controlled ventilation reduces exposures by eliminating
numerous sources of dust from packing and bag handling
Operations. Also, the number of employees directly
involved is greatly reduced.

Plastic wrapping or covering of loaded pallets - Dust
dispersion from bags may be further reduced by plastic
covering or wrapping (either shrink wrap or stretch wrap)
of loaded pallets. This technique reduces the breakage of
bags during warehousing and shipping (Photo 19). It also

36


Spraying Water on Bags

15. Spray nozzles (above and below) wash bags

16. Spray inside conveyor housing agglomerating dust

34


B.

Industry Description

1.

Process description

The following descriptions are limited to the production and dust
control systems observed in this investigation. There may be
other processes and procedures common to the silica flour industry
which were not evaluated.

Mining

Sand ores vary from one mine to the next. The ore may be mined
from a hard rock formation yielding quartzite or from a loosely
cemented deposit, such as found in the St. Peter's Formation. The
ores primarily consist of crystalline silicon dioxide (quartz) and
may contain small amounts of impurities, e.g., iron and clay. Any
overburden is removed and the ore is mined from an open pit or
quarry. Some ore is also obtained from underground mines.
However, this was not observed in this study. The deposit is
usually drilled and blasted to loosen the material. Ore from
hardrock deposits is loaded into trucks, transported to the
primary crusher (usually located near the quarry) and reduced to
minus 6-inch rock. For loosely cemented sand deposits, the
material is hydraulically mined. The sand (mostly minus 1/8 inch)
flows to a sump and is pump through a pipeline to the mill.

Milling

The mill may be located adjacent to or several miles from the
quarry. The hardrock ores are transported either by an overhead
bucket tramline or over a series of conveyor belts from the
primary crusher to the secondary crusher. Usually, covered
conveyor belts are used to move the ore through the remainder of
the comminution processes. Secondary and, in some cases, tertiary
crushers and rod mills are used to comminute the ore. The ore
from the quarry is usually damp and remains damp through the
crushing stages. Water is added during grinding in the rod mills.

The ore is then wet-screened to minus 1/8 inch as it comes from
the rod mills or the quarry. It is dewatered and usually pumped
as a slurry, through a pipeline or moved by covered conveyor belt
to the next process. The next process may be either the stock-
piling of "steel" grade sand; or vacuum filtering of the "steel"
grade sand; or benefication of the sand ore (such as flotation to
remove slimes) to upgrade it to a higher quality "glass" grade
sand. The sand is dried and stored in silos or bins. Open
conveyor belts are used to move the ore through the benef ication
processes. Usually, covered conveyor belts are used to transport
the dried sand to the storage silos.

A portion of the "glass" grade sand is milled in pebble or tube
mills. These mills are lined with silica blocks and use silica
pebbles or ceramic plugs as the grinding media. The "glass" sand
is dry ground to produce silica flour products ranging in size
from 5 micrometers(um) to 74 um (minus 200 mesh). Solid particles

4


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suny [equawt4adx3 omy BuLung
suotyeuquaauo) 3sng atqesrdsay “/ alqey

46




Go

For the semi-automatic system, the bags are manually placed on the
packer spouts, filled, and either hand-tipped or automatically
ejected onto a conveyor. They are then transported either to an
intermediate loading (palletizing) point or directly into a truck
or boxcar. The bags are then manually stacked in the shipping
vehicle.

The bags are usually transported by belt, spring, gravity wheel,
or other types of conveyors from the packing station to the
loading or palletizing stations. These stations may be located on
the same or different floor level. When bags are palletized at an
intermediate loading point, a fork lift is used to transport the
loaded pallets either into a truck, boxcar or to a storage area.
When loaded pallets are placed in storage, they may be plastic
wrapped (shrink or stretch) or covered with plastic bags. This
reduces leakage and environmental contamination, and increases the
weatherability of the pallet loads.

Dust control

Normally, minimal ventilation is required for dust control for the
processes between quarrying and drying because the ore is either
damp or being treated in a wet process. Extensive ventilation is
required, however, to control dust dispersion after drying,
especially in the flour processes of bagging, bag loading and bulk
loading. These ventilation systems are usually connected to
baghouses in which the captured dust is returned to product bins
rather than exhausted into the atmosphere.

Other effective methods used to control dust, in addition to
ventilation, include wet washing, mopping with kerosene emulsions,
and vacuum cleaning.

Scope of Study

The potential for hazardous exposures to silica dust exists throughout

the silica flour/sand industry. These exposures may occur during

mining, sand and flour processing, and final product usage. The major

emphasis of this assessment, however, was limited to exposure control
during the packing, handling and shipping of the flour products. The
four aspects of hazard control technology - engineering, environmental
monitoring, work practices and use of personal protective equipment -

were evaluated either quantitatively or qualitatively. The major

emphasis in this study was directed toward the evaluation of
engineering controls.


DISCLAIMER

Mention of company names or products does not constitute endorsement by the
National Institute for Occupational Safety and Health.

DHHS (NIOSH) Publication No. 84-110

ii


b) Transfer between conveyors

Two locations were observed where filled bags were transferred
between conveyors. At one location, transfer was manually
assisted (Photo 5 and Figure L). A ventilated hood, close to
the transfer point, developed in-let air velocities of 20 to
40 fpm. This air movement was insufficient to capture all of
the generated dust. Dust levels averaged 400 ug/m3

respirable dust and 35 ug/m> respirable dust during normal
operations (Table 3.7). Spilled dust from broken or dirty
bags was periodically removed by washing down of floors.

PACKING AREA | WATER

SPRAYS

EXHAUST

FROM PACKER VENTILATION

CANVAS CURTAIN

ROLLERS

a —__ ROLLERS
SS

TRANSFER CONVEYOR

[crouno FLOOR LOADING AREA

Figure L: Transfer Points - Ventilation and Water Sprays

At the second location (Photo 5 and Figure I), transfer
between conveyors was automatic, with minimal manual handling
of bags. Although no enclosure or ventilation was present at
the transfer point, dust levels were low during packing
operations, averaging 66 ug/m3 respirable dust and

66 ng/m3, respirable silica dust (Table 7.3). This control
condition was probably caused by several factors: 1) bags
were Cleaned during their transport along the horizontal chain
conveyor by a ventilation system of four hoods (2 above and 2
below the conveyor); 2) the drop between conveyors was less
than two inches causing minimal dispersion of dust to the
atmosphere; 3) bag breakage was minimal, less than 2%, both
during bag transport and during packing and pallet loading;
and ay excessive flour, not captured by the ventilation ducts,
fell through the chain conveyor into one of two hoppers and
returned to storage silos.

27


RESPIRABLE OUST CONCENTRATION 1g /m?

7000;

TTT TT

!so0

!000)

Soo
40)
300
coo

a Oe

(og

Loading into boxcars and trucks

Boxcar and truck loading directly from conveyor belts is a major
source of dust dispersion (Figure D). Table 2.6b and c shows
respirable silica dust levels ranging from 264 to 1625 g/m
under normal operating conditions. (Photos 8, 9, 10). Although
no evaluations were made of loading palletized product into
boxcars or trucks by forklift, it may also be a major source of
atmospheric dust.

Bulk loading of hopper cars

Bulk loading of closed railroad hopper cars can be accomplished
with (dispersion) minimal dust dispersion, when performed under
the control of local exhaust ventilation (Photos 11-14 and
Figure D). Table 2.7 shows that the average respirable silica
dust level around a controlled loading spout is 80 yg/m3, This
is higher than the background upwind dust level of 35 ug/m3, at
this plant, but below the MSHA standard.

QUST CONTROLS
8 - Ventilation Onhy

Q- Ventilation with Water in Product
E - Ventilation with Water Sprayed on Bags

C- Ventilstion with Water in Product and on Bags [0+]

n BACKGROUND
= - Gutdoors Upwind Respi
d- Qutdoors Downwind aly Silica
Qust

[3 Locations } {1 Location)

A

BadBead Gad
i TLV SILICA = 100 g/m?

wo llanoon TAS

foxcars and Closed Trucks - Bags Bulk

Figure O: QUST CONCENTRATION ar LOADING

15

Respirable


HEALTH HAZARD CONTROL TECHNOLOGY ASSESSMENT
OF THE SILICA FLOUR MILLING INDUSTRY

by

Paul E. Caplan, P.E., C.1.H.,
Laurence D. Reed,
Alfred A. Amendola, P.E.,
and
Thomas C. Cooper

U. S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service

Centers for Disease Control
National Institute for Occupational Safety and Health

Division of Physical Sciences and Engineering
Cincinnati, Ohio 45226

October 1984


probable source. For example, in a packer area, if the
primary source of airborne respirable dust were the packer
machine and/or filled bags, the silica content of an airborne
dust sample or rafter sample would be high (70 to > 90%
silica). However, if the primary source of the contamination
were outside (ambient) dust, an airborne dust or rafter sample
would be lower in silica content (less than 50%). This type
of evaluation could indicate the effectiveness of a local dust
control system in comparison to the general dust control of
the area; it could assist in decisions for improving dust
control design.

c) Area samples were collected to estimate average atmospheric
dust concentrations of specific work locations, over an
extended period of time (several hours). Work area samples
were collected with MSA Gravimetric Dust Samplers using
cyclone preseparators to remove non-respirable (> 10 um)
particles. At all plants, MSHA's periodic monitoring was the
major source of available environmental data.

Medical monitoring

Although this study did not include an evaluation of the medical
monitoring programs, such programs are essential in this
industry. They are now being provided at each of the three
companies visited. These programs are described in the NISA,
report "Occupational Health Program for Exposures to Free
Crystalline Silica."(1 They should include periodic (annual or
biennal) chest x-rays and pulmonary function testing for all
personnel potentially exposed to silica dust.

Work Practices

Good work practices and effective housekeeping procedures are
essential for maintaining dust exposures at a safe level. These were
also evaluated qualitatively. At each plant evaluated, management has
estimated that as much as one-half of their dust control program
involves effective housekeeping and maintenance procedures. Some
effective work practices include:

1.

If incentive pay plans are used, they should take into consider-
ation the necessity for prompt clean-up of dust spills and allow
time for this function. All ill-conceived incentive pay plans may
result in poor housekeeping and poor work practices, especially
bag handling.

Proper bag handling during placement on pallets, conveyor belts,
or during stacking in boxcars is essential for minimizing dust
dispersion. This precludes such practices as throwing or dropping
(instead of placing) of bags, which results in bag breakage and
dust dispersion.

39


sant ensnefoscx ev
nano,

J poor

onarine aicken | cotihtn
FAH —+
ae
ETT Ty ewes eomeee [Ste JES
tOree
re
_—
PLAN VIEW

dP

on
“as
oititbne(| |
a
‘BASS AND §
PALLET. =|
SCREW COMVE

CROSS SECTION
Figure G: Packing Area - Main Product

AT FACE OF PACKER
Figure H: Ventilation at Main Product Packing Area

23


Table 4. Effect of Addition of Deter MicroFoam(R)
to Sand Products
(Company data)

Total Dust Concentration
Location Without Deter with Deter Reduction

(mg/m*) (mg/m?) (%)

Screen Building 5th Floor -
inside conveyor 4 ft. from 218 175 20

Deter(R) nozzle

Screen Building inside
conveyor transfer point 164 1 33

to storage site

Bulk loading covered hopper

railroad car, inside hopper 84 27 67
(R) - Deter MicroFoam, manufactured by Deter Company, Inc.
mg/m - milligrams per cubic meter of air

32



Bulk Loading in Closed Hopper Car

13. Bulk loading closed railroad hopper car with exhaust;
fill-spouts and exhaust

14, Bulk loading closed railroad hopper car with exhaust

18


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3. Spills should be cleaned up as soon as possible after they occur
(by vacuum or wet cleaning) to minimize dust dispersion into the
atmosphere.

4. The practice of uncontrolled cleaning of workers! clothing with a
high pressure air hose, is both a safety and a health hazard.
MSHA regulations(12) prohibit the directing of compressed air
toward a person. The use of vacuum cleaning of clothing is less
hazardous both from a safety and a health viewpoint.

5. A regularly scheduled inspection and prevent ive maintenance
program is essential for effective dust control. This should
include an evaluation of equipment and performance of ventilation
systems. The environmental control maintenance staff should be as
well trained and experienced as the production maintenance staff.
The use of duct tape and other means of temporary repair instead
of permanent repair of equipment should be minimized.

Respiratory Protective Program

The proper use of personal protective equipment (PPE) js an important
part of an effective hazard control program. A Complete PPE program

consists of procedures for protection of the respiratory system, head,
eyes, ears, feet, and whole body. A critical aspect of this program

is respiratory protection in the silica flour industry.

Because respiratory protection plays such a critical role in worker
protection, one employee, accountable to the plant manager, should be
responsible for the proper selection, fitting, training, cleaning,
inspection, maintenance, and storage of respirators. In addition, one
portion of the plant area should be ‘designated for these procedures.

Detailed information about the selection of respirators can be
obtained from the joint NIOSH/OSHA Respirator Decision Logic. 7)
Adequate respiratory protection for most of the Process areas studied
can be achieved with any NIOSH approved(18 half-mask, quarter-mask,
or single-use respirator with its appropriate particulate filter.

40


The spraying of water onto the outer surfaces of filled bags
reduced dust levels by an average of 67%, Particularly around
packing, bag handling, and boxcar loading operations.

The combination of water spraying and injection of water into
products resulted in overall reductions of dust of approxi-
mately 70%.

Bulk loading of silica flour into closed hopper cars can be well
controlled by the use of local exhaust ventilation. Two systems
were observed. In the first system the product was loaded into
the hatch and air was exhausted from the same hatch. In the
second system, the product was loaded and air exhausted through
different hatches. Both methods appeared to be equally effec-
tive. All companies plan to increase their handling and shipping
of product by bulk and to centralize bulk handling facilities.

Several additional engineering procedures and processes reduced dust
exposures.

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Bo

The installation of plastic strip curtains between rooms or work
areas reduced air cross currents. These overlapping strips permit
easy traffic flow and increase the effectiveness of local exhaust
control systems.

The use of plastic covers or wrapping (stretch or shrink) around
pallet loads reduces bag breakage and dust dispersion during
pallet handling and storage. It also increases weatherability of
exposed pallet loads during storage and shipping.

The installation of automatic bag ejectors, auger feeders on
packing machines, the use of stronger 3-ply bags, and better
designed feed spouts, result in reduced dust leakage during bag
filling operations.

The transfer of primary and intermediate materials as a wet slurry
through pipes, instead of transfer on conveyor belts, in a dry
form, greatly reduces fugitive dust emissions.

Transfer between conveyors should be performed with minimum drop
distances and minimal manual handling.

Good work practices are essential for maintaining effective contro] of
dust sources.

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Product spills should be cleaned up immediately using wet sweeping
or vacuum cleaning equipment.

Proper bag handling techniques should be encouraged, which include
placing of bags (instead of throwing or dropping) on pallets and
careful handling of broken bags.

Clothing should be cleaned by vacuum air.

42


are generally sized according to a screen mesh system, either the
Tyler or the U.S. Sieve series, as shown in Table 1. The flour is
sized and pneumatically transported to storage bins or silos.
Most of the "Steel grade sand, "glass" grade sand, and silica
flour is shipped by bulk. Closed and open trucks and closed
railroad hopper cars are normally used to ship bulk whole grain
sand and flour. The remaining sand and flour is bagged for
shipping by truck or boxcar.

Table 1.

Equivalence of Screen Mesh to
Particle Size, U.S. Sieve and
Tyler Sieve Series (16

Mesh Opening — umTM
size U.S. Sieve Tyler
5 3962 3962
10 1981 1651
20 833 833
60 246 246
100 147 147
200 74 14
325 43 43
400 38 38

*um = micrometers

Packer machines vary in design and operation. The pneumatically
operated, forced-flow, filling system is most commonly used, with
one to four fill spouts. Auger feed is normally used to pack the
smallest size particle flour (5 um) through a single-spout
packer. Normally, each packer machine has its own exhaust
ventilation system. Several machine ventilation systems are
connected to one main system.

Manual or semi-automatic flour packing systems are used to fill
multi-ply, valve-type paper bags. For the manual system, the bags
are placed on the packer spouts, filled, removed and palletized.
Packing and palletizing operations are located adjacent to each
other.