n ae.

(DC

MN Mie PEOPLETM

Technolo
News By

No. 486

Milestones in Mining Safety and Health Technology

March 2001

Floor Heaters Can Increase Operator’s Dust
Exposure in Enclosed Cabs

Objective

To reduce equipment operator exposure to respirable dust in
enclosed cabs by examining the effectiveness of retrofitting air pres-
surization and filtration systems on existing cabs.

Background

Many types of heavy equipmentare used in mining, construction,
and agriculture. Most have enclosed cabs to protect the equipment
operator from excessive dust and noise exposure, When the equip-
ment is new, controls are normally implemented into the cab to keep
these exposures at acceptable levels. However, as this equipment
becomes older, many components of the enclosure deteriorate, such
as gaskets and seals. This causes the effectiveness of the enclosed
cab to be greatly reduced. Once this occurs, the equipment operator's
dust exposure can increase to hazardous levels. In surface mining
operations, elevated exposures to crystalline silica have caused an
excessive incidence of silicosis.

Approach

A cooperative research study with a mining operation and a cab
filtration company was conducted to evaluate the effectiveness of
retrofitting an older surface drill with two controls to lower the drill
operator's respirable dust exposure, These two controls were:

(1) A good air filtering and pressurization system to ensure that
clean air was delivered into the enclosed cab. Ideally, the incoming
air filter should be 99% efficient in removing particles with an aero-
dynamic diameter of 0.3 um or greater from the airflow.

(2) ‘Sufficiently sealing the cab to develop a positive static pres-
sure and ensure that dust was not leaking into the cab. This was done
by plugging all holes and cracks and maintaining good gaskets and
seals, To prevent wind from forcing contaminated air through holes
in the cab, the cab’s static pressure must be greater than the wind's
velocity pressure,

During the course of this research, it was found that a floor
heater fan used in the drill during the winter months greatly increased
the operator's respirable dust exposure.

Problem Identification

Four days of background dust levels were measured as a baseline
for this research, These baseline measurements were taken in May
2000 when air temperatures ranged from 60° to 70°F, When this was
completed, the two controls were implemented. The first control was
to install an improved air filtering and pressurization system on the
enclosed cab. This was composed of a two-stage prefilter, a blower,
then the respirator-medium secondary filter. Since the secondary filter
was on the positive side of the fan, all air delivered into the enclosed
cab had to pass through this secondary filter. After the filtering system
‘was installed, the cab was pressurized to a static pressure of 0.01 inches
of water (w.g,), which is still very minimal. The second control was to
seal the cab. New door gaskets were installed, and all cracks and holes
in the shell of the enclosure were plugged. This increased the cab
pressurization to approximately 0.1 inches w.g.

With these changes implemented and everything working prop-
erly, the identical dust analysis was repeated to determine the effect
on the drill operator's dust exposure. The posttesting dust measure-
ments consisted of 2.5 days of testing in November 1999 and 2 days
of testing in January 2000. Since this testing took place in winter
conditions with low outside air temperature, the cab had to be heated.
The heater unit used in this enclosed cab was a radiator heater
located near the floor (figure 1). This is a very common type of heat-
er used in many types of heavy equipment.

Figure 2 shows the respirable dust levels inside the enclosed cab
for both pretesting (baseline) and posttesting (with floor heater in
cab). NIOSH anticipated that in the posttests, dust levels would de-
crease because of the improvements made to the cab. Instead, re-
spirable dust levels increased from 0.04 mg/m? during pretesting to
0.68 mg/m’ during posttesting. NIOSH hypothesized that the floor
heater in the cab was the primary cause of this dust increase. It was
believed that dust was generated from the drill operator's boots

ay

ea

y U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
Centers for Disease Control and Prevention
National Institute for Occupational Safety and Health


grinding and stirring up material on the floor and from dust being
blown off of the operator's clothing.

The drill was taken into the shop, and testing was done with
optical particle counters to evaluate whether the floor heater was the
significant source of dust contamination to the drill operator. Ini-
tially, the first test was to monitor particle levels with only the air
filtration and pressurization system operating (figure 3, test 1). Next,
the recirculation system was operated, which also provides air
conditioning to the cab in the summer months (test 2). The re-
circulated air in this second ventilation system was not filtered.
Finally, both systems were operated along with the floor heater
(test 3). Once this test series was completed, another series was re-
peated, with the particle-counting instruments switched from outside
to inside the cab to minimize the effects of any instrument biases.

The results confirmed that the floor heater was the dust source.
Inside cab concentrations averaged 0.01 mg/m’ for test 1, 0.03 mg/m?
for test 2, and 0.26 mg/m’ for test 3 when the floor heater was
operating. The concentrations for test 3 were a ninefold increase over
those for test 2 and a 27-fold increase over those for test 1. Figure 3
also indicates that respirable dust levels inside the cab were higher than
those outside the cab when the floor heater was used.

The perspective on enclosed cabs has always been to provide clean
air into the enclosure and maintain pressurization to keep dust from
coming into the cab from outside. The floor heater problem identified
in this research adds a new perspective to providing dust protection to
the operator in the enclosed cab. The floor heater is a serious problem
because the floor is the dirtiest part of the cab, since the operator brings
a significant amount of dirt into the cab floor on his or her work boots.
Then, as the operator moves his or her feet around in the cab, dust is
created, which is then blown throughout the enclosure by the fan on the
floor heater. The fan on the floor heater also tends to stir up dust that
may be on the drill operator's clothes.

Recommendations

Because of the significant increase in dust levels with the floor
heaters, NIOSH recommends that they not be used in their present
location. If needed, they should be repositioned to a higher area in
the enclosure where they are less prone to pick up dust from the floor
and the operator's clothes. The best solution would probably be to
implement a heating and air-conditioning unit into the clean air and
pressurization system.

In addition to removing cab heaters from the floor, this study
identified two ways to minimize the problem of dust generation inside
of cabs. First, use a highly efficient recirculation filtration system to
capture dust that is generated by the operator or other sources inside the
cab. Second, practice good housekeeping by keeping the floor and
other intemal cab surfaces as clean as possible. Also, keep the
operator's clothing and boots as clean as possible.

For More Information

For more information about controlling dust levels in enclosed
cabs, contact Andrew B, Cecala or John A. Organiscak, NIOSH
Pittsburgh Research Laboratory, Cochrans Mill Rd., P.O. Box 18070,
Pittsburgh, PA 15236-0070, phone: (412) 386-6677 or (412) 386-
6675; fax (412) 386-4917; e-mail: aicl @ede.gov or jdo3@ede.gov;
or William A. Heitbrink, NIOSH Division of Applied Research and
Technology, 4676 Columbia Parkway, Cincinnati, OH 45226,
phone: (513) 841-4376; fax: (513) 841-4506; e-mail:
wah2@cdc.gov.

To receive additional information about occupational safety
and health problems, call 1-800-35-NIOSH (1-800-356-.
4674), or visit the NIOSH Web site at www.cdc.gov/niosh

Mention of any company name or product does not constitute
endorsement by the National Institute for Occupational Safety
and Health.

Figure 1.-Location of heater inside enclosed cab of drill.

El Baseline § Floor heater

&

2
be

S
ES

RESPIRABLE DUST CONC.
INSIDE CAB, (mg/m)
o e
& &

Day#1 Day#2 Day#3 Day #4

DAYS OF TESTING

Figure 2.—Drill operator's respirable dust exposure with
and without floor heater.

Day #5

[EiTest 1 EiTest 2

‘est 3

©
is

(mg/m)

Ed

RESPIRABLE DUST CONC.,

Outside
SAMPLE LOCATION

Figure 3.—Shop testing to determine increase in drill operator's
respirable dust exposure with floor heater.

Inside