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No. 485

Milestones in Mining Safety and Health Technology

February 2001

Improved Cab Air Inlet Location Reduces Dust Levels
and Air Filter Loading Rates

Objective

To improve operational effectiveness of enclosed cab filtration
systems.

Background

Enclosed operator cabs are widely used on mobile excavation
equipment in the mining and construction industries. They protect the
operator from bad weather, noise, and airborne dusts. The inside cab
environment usually must be kept at very low dust concentrations
because of quartz dust generated from the excavation of silica-bearing
rock. Most cab designs achieve heating and air conditioning effective-
ness by recirculating most of the interior cabin airflow, with a smaller
portion of the outside air added to the cab as makeup air. Both the re-
circulated cab airflow and exterior makeup air added to the cabin
should be efficiently filtered, with the makeup air positively pres-
surizing the cab interior. Ideally, operator cab air filters should provide
at least 99% capture efficiency for dust particles as small as 0.3-ym
aerodynamic diameters. These higher efficiency air filters provide
good dust control for the equipment operator, but tend to accumulate
dust more quickly than lower efficiency air filters.

Approach

The location of the cab air inlet is a key design factor that could
affect the overall performance of air filtration systems. Locating the cab
air inletnear the equipment's source of dust generation can subject the air
filtration system to high dust-loading rates. High dust-loading rates tax
air filtration systems and reduce their effectiveness. The higher pressure
drop across a loaded filter decreases air system quantity and increases the
possibility of dust leakage around the filter. Reduced air system quantity

decreases cab pressurization. Thus, air filters need to be changed or
cleaned often to optimize air system performance. Finally, air filter per-
formance is usually a relative dust capture efficiency (on a percentage
basis), so filtration of higher outside cab dust levels can result in higher
inside cab dust levels.

The cabair inlet should be strategically located away from the equip-
ment's dust sources to reduce dust loading of the air filtration system.
This usually means placing the cab air inlet at higher distances from
ground level.

How It Works

Field studies were conducted at several surface coal mines to
measure dust levels at several locations around the cabs of Caterpillar
(CAT) DIIN and DION bulldozers during their overburden removal
operation. The cab air inlets on these bulldozers are located both be-
neath and between the rear part of the cab and fuel tank. Personal
respirable dust samplers were placed on the back side of the elevated
drive axle (under the fuel tank and cab air inlet) and on each side of the
rollover protection frame of the cab (above the fuel and hydraulic
tanks). Figure 1 shows the dust sampling locations on a CAT DIIN
bulldozer. The axle sampling location is about 6 ft above ground level;
the cab sampling locations are about 11 ft above ground level.

Figure 2 shows the dust level relationship measured between the
field sampling locations on the bulldozers. This relationship shows that
the dust levels at the bulldozer axle location (under the fuel tank) are
between two and three times higher than those along the sides of the cab
(above the fuel and hydraulic tanks). These findings suggest that the
bulldozers’ dust levels and cab air filter loading rates can be reduced by
increasing the air inlet distance away from the ground level dust sources.
Other air inlet location considerations should include which side of the
equipment provides the best location, accessability of the inlet filter, and
the location of the engine exhaust. Placing the cab inlet air location on

es

y U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

& Public Health Service

Nava

Centers for Disease Control and Prevention
National Institute for Occupational Safety and Health


the back or rear side of the cab may expose it to the dust plume trailing
behind the equipment when itis traveling forward. Although many front-
end loaders, drills, and agricultural tractors place their air inlets on top of
the cabs, this may not be practical for some off-road haul trucks where
the dump bed is located over the cab. However, if the air inlet is placed
ina location where dust levels are typically lower, the filter-loading rates
and maintenance requirements should be lowered.

For More Information

For more information about controlling dust levels in enclosed cabs,
contact John A. Organiscak or Steven J. Page, NIOSH Pittsburgh Re-
search Laboratory, Cochrans Mill Rd. P.O. Box 18070, Pittsburgh, PA
15236-0070, phone: (412) 386-6675 or (412) 386-6669, respective-
ly, fax: (412) 386-4917, e-mail: jdo3@ede.gov or sep8@ede.gov,
respectively.

Figure 1.-Surface mine excavation with a CAT D11N bulldozer.

Toreceive 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.

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Dust Levels Along Cab, mg/m3.

0.0 Tr T
00 05 #10 15 20 25
Dust Level at Drive Axle, mg/m3

Figure 2.Relationship between dust sampling loca-
tions on bulldozers.