Figure

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Improved Dust

Control for

Handl

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-J

ers

On-site tests lead to minor modifications to a bag-palletizing

system that significantly reduce

workers I dust exposure

BY ANDREW B. (ECALA, JEANNE A. lIMMER, BRAD SMITH

AND STEVE VILES

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Components of Malvern Minerals' semi-automated bag-palletizing system.

MEASURING RESPIRABLE DUST

~ ecent report evaluating silica exposure levels in

ilie metaJ/nonmetal mining industry noted iliat bag

ackaging and loading are some of ilie occupations

at ilie greatest risk. In addition to dust problems, ilie bagstacking process is labor intensive, making lost-time injuries common due to back fatigue and strains.

During ilie bag-stacking process, a significant amount

of dust can be generated, mainly &om product on ilie outside of ilie bags and &om dust escaping ilie bag valve upon

impact of ilie bag on ilie pallet.

In an effort to address dust-exposure and back-fatigue

issues, Malvem Minerals Co., Hot Springs, Ark., made

two major improvements to its ground silica stacking facility. First, ilie company purchased a semi-automated bag

palletizing system (Figure 1 ). Wiili iliis system, the bag

stacker does not lift ilie bags, but slides iliem across a metal

table. Small jets of air exit through perforations in ilie table

top (similar to an air hockey game), allowing workers to

more easily slide each bag into ilie proper position.

After each layer of bags is completed, ilie table slides

open, and ilie entire layer of bags is loaded onto an underlying pallet. The table ilien closes, readying it for anoilier

layer of bags. After ilie entire pallet is loaded, ilie unit delivers ilie pallet to a shrink wrap and forklift pick-up area.

In addition to this semi-automated palletizing unit,

Malvern Minerals purchased an Overhead Air Supply Island System (OASIS) to lower ilie bag stacker's dust exposure. The oAsIS takes outside air, directs it ilirough

The bag stacker's respirable dust exposure was monitored using a RAM-l instantaneous dust monitor to evaluate the impact of the various changes on the palletizing

process and dust-control equipment. The bag stacker

wore a vest that held the lo-mm Dorr-Oliver cyclone,

which classifies the respirable portion of dust. Flexible

tygon tubing was used to connect the cyclone to the

RAM-l dust unit, allowing the bag stacker to perform the

palletizing process with minimal interference.

The RAM-l measures respirable dust concentrations

by light scattering with a sensing chamber. This device

closely simulates gravimetric measurements when cali-"

brated for a specific dust. This instrument is ideal for"

comparative evaluations, as was the case in this study.

Since the RAM-l is not an MsHA-approved instrument for dust compliance sampling, the dust concentrations listed in this article should be used as a comparative value of respirable dust concentration and not

to determine actual dust concentrations from a compliance standpoint.

Exhaust

system

Se

/
Figure 2

Dust Concentration. (RAM units)

I. Air Slide On. Air Slide offl

200

Comparison of a bag stacker's average dust exposure for

particular product mesh sizes-with and without the air

slide operating.

After analyzing the test results, NIOSH made four rec-1

ommendations to Malvem Minerals Co. (Figure 3):

Recommendation 1- Turn off the air to the slide

table. This minimized dust being entrained by the air jets

and carried up over the bag stacker into the exhaust ventilation hood. However, turning off the air jets also negated the purpose of the air slide, which was to minimize the

effort and stress placed on the bag stacker to slide and position a bag on the table. Therefore, a spray lubricant was

used on the table top. However, this lubricant spray had a

very minimal and short-term effect. This first recommendation was an interim solution.

Recommendation 2-Change the design on the exhaust hood. The exhaust hood was modified, removing the

angled front and maintaining a significant distance from

the worker to the hood opening across the entire front of

the hood. Once modified, the bag stacker was not physically able to place his upper torso under the hood, thus

lowering his dust exposure.

Recommendation 3-Hang clear plastic stripping

around the discharge of the OASIS system. This helped

to separate the clean air from the dust-laden air around

the palletizing unit. The stripping also provided to the bag

stacker a physical indication of the clean-air barrier. The

worker could lean into the stripping, but once he extended to a certain point, he broke through the stripping, and

two filters, then delivers clean air down over the bag stacker. During test.5, approximately 1,600 cfm of filtered air

exited the OASIS.

After implementing this new equipment, the bag stacker's respirable dust exposure remained at unacceptable levels. Therefore, Malvern requested the assistance of the

National Institute for Occupational Safety and Health

(NIOSH). Initially, NIOSH performed a three-day analysis to determine factors impacting the bag stacker's dust

exposure then made recommendations to create a more Figure 3

effective dust-control design.

After Malvem implemented a number of these recommendations, the bag stacker's dust exposure was significandy reduced and has remained at acceptable levels dur., (

ing in-house and Mine Safety and Health Administration

dust-compliance sampling. Five months later, a follow-up

t'

analysis was performed to determine the relative effects

that the recommendations had on lowering the bag stacker's dust exposure. .,;

# 4: Move OAStS unit 18- 24 inches

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,# 2: Modify

exhoust

hood

# t Turn air

slide off

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Seeking the dust source

For NIOSH's initial evaluation, the pallet-loading system

was operated normally for the first two days and was modified for the third day. Observing the bag stacker's work

practices and monitoring his respirable dust exposure for

days one and two, NIOSH found that a significant part of

the bag stacker's dust exposure occurred from the air slide

on the palletizing machine.

As the bag stacker leaned forward to position the back

bags on the table, he sometimes placed his upper torso into

the front side of the exhaust hood. The air slide on the semiautomated palletizing machine entrajned dust from the bags

and carried it past the worker into the exhaust hood.

In an effort to verify this occurrence, the air supply was

disconnected from the slide table during testing on day

three. The bag stacker's respirable dust exposure decreased

4.5 to 10.7 times with the air table turned off (Figure 2).

I~

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iP-:.;.

Modifications recommended by NIOSH to reduce the bag

stacker's dust exposure.

L207A 325

Product Mesh Sia
Figure 4

Dust ConrentratioD, (RAM units)

200 325 12SO UO7A L337

Product Mesh Si22

I. Air Slide 00 .Air Slide Offl

Comparison of a bag stacker's average dust exposure for particular product mesh sizes (with and without the air slide operating) after modifications to the palletizing system.

forward. Since the OASIS is a heavy unit and includes

metal duct work from the outside wall and main filtering

unit, moving the discharge end would have been difficult

and costly. Malvem Minerals elected to detern1ine the impact of the other modifications before incurring this effort and expense.

Preliminary dust testing performed in-house by

Malvem Minerals indicated that the first three modifications had a measurable impact. A second comprehensive

evaluation performed by Malvern, NIOSHand MSHA

detern1ined the relative impact that these changes had on

lowering the bag stacker's respirable dust exposure.

In the initial evaluation, the bag stacker's dust exposure

increased 4.5 to almost 11 times with the air slide on versus

off. During the second evaluation, dust exposure reductions

ranged from 2.5 to 3.5 times the bag stacker's initial dust concentration. The primary reason for this reduction was the

change in the exhaust hood. Placing plastic stripping around

the discharge of the OASIS device further reduced the impact of the air slide to almost no effect.

Because these modifications were successful, it was decided that the use of air on the slide table to aid workers LOWERING DUST ExPOSURE

in moving bags, thus reducing the likelihood of back injury, outweighed the negative consequences of'the minimal increase in dust exposure. After about 14 months, dust -

exposure testing by Malvem Minerals and MSHA showed

that the bag stacker's respirable dust levels have remained

at acceptable concentrations (Figure 4). a

ANDREW B. CECALA IS A MINING ENGINEER AND JEANNE A. lIMMER IS A PHYSICAL SCIENCE TECHNICIAN WITH THE NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH, PITTSBURGH RESEARCH

LABORATORY; BRAD SMITH IS VICE PRESIDENT/SAFETY MANAGER

FOR MALVERN MINERALS CO., HOT SPRINGS, ARK.; AND STEVE VILES

IS A DISTRICT HEALTH SPECIALIST WITH MSHA, DALLAS, TEXAS.

Based on tests and modifications of Malvern Mineral's

bag-palletizing operation, the following changes may

help lower bag-stacker dust exposure at operations

using similar equipment:

.If semi-automated palletizing units are used with

an air slide, make sure the air slide is not blowing

dust up onto the worker. Using the OASIS in conjunction with the semi-automated palletizing unit is effective, but the OASIS device must be positioned to

cover the entire range of motion for the worker. If the

unit was properly positioned at Malvern Minerals, it

probably would have eliminated most of the problems initially encountered.

.If using a semi-automated palletizing system in conjunction with an OASIS system, consider using plastic

stripping around the OASIS discharge. This helps separate the clean air from the dust-Iaden air around the

palletizing unit and gives the worker a physical indication of when he or she is extended out past the end of

the ciean-air zone.

.Never use an exhaust hood that creates a need for a

worker to place his upper torso (breathing zone) into

the hood to perform a job function. Additionally, workers should not position themselves between the dust

source and the exhaust hood. This causes the dust to

flow directly past the worker and significantly increases

worker contamination and dust exposure.

REFERENCES

Watts, W.F. and D.R. Parker, "Quartz ExpoSUre Trends

in Metal and Nonmetal Mining." Appl. Occup. Environ.

Hyg., 10 (12), p. 1009-1018 (1995).

WIlliams, K.L and R.j. Tlmko, "Performance Evaluation

of a Real- Time AeroSOl Monitor." USBM IC 8968, 20 p.

(1984).

Votkwein, j.C.; M.R. Engel and T .D. Raether, "Get Away

from Dust with Clean Air from Overhead Air Supply Island (OASIS)." Rock Products (1986).

would be aware that he was no longer protected by the

clean envelope of air provided by the OASIS.

Recommendation 4-Extend the OASIS discharge

18 to 24 in. toward the palletizing unit. This ~ould also

eliminate the chances of the bag stacker leaning too far