Improve Drill Dust Collector Capture Through Better Shroud 

and Inlet Configurations 

Objective

 To improve the effectiveness of dust collector capture on 

surface mine drills. 

Background

 Overexposure to airborne respirable crystalline silica (or 

quartz) dust can cause serious or fatal respiratory disease. In 

particular, some of the most severe cases of silicosis have been 

observed in surface mine rock drillers. A voluntary lung 

screening study conducted on surface coal mine workers in 

Pennsylvania concluded that the incidence rate of silicosis is 

directly related to age and years of drilling experience. Dust 

sampling data from the Mine Safety and Health Administration 

show that the drilling machine operator continues to frequently 

exceed the federally mandated quartz dust standard. 

 Dry dust collection systems tend to be the most common 

type of dust control incorporated into drilling machines by 

original equipment manufacturers because of their capability to 

operate in various climates. This system includes a selfcleaning (compressed air back pulsing filters) dry dust collector 

sucking dust from underneath the drill deck shroud, which 

surrounds the hole being flushed by compressed air (bailing air). 

Previous drill studies have shown that over half of the dry 

collector dust emission problems are from the deck shroud and 

drill stem bushing leakage. 

Approach

An obvious cause for dust escaping collector inlet capture is 

a breach in the shroud enclosure around the hole. The amount 

of dust escaping through shroud enclosure openings depends on 

many factors. These include the opening size, the drill hole 

flushing airflow, the collector airflow, and the opening location 

from the inlet duct. Experiments were done at the NIOSH 

Pittsburgh Research Laboratory to study the effects of these 

factors in mitigating dust that escapes the dust collector shroud. 

Between 170 and 179 L/sec (360 and 380 ft3

/min) of a dusty 

mix (rock dust) of compressed air was blown out of a 20.3-cm 

(8-in) simulated drill hole annulus at discharge velocities 

between 23.4 and 24.9 m/sec (4,600 and 4,900 ft/min). A 1.52-

m-wide by 1.22-m-deep by 1.22-m-high (5-ft by 4-ft by 4-ft) 

replicate drill deck was shrouded over and around the simulated 

drill hole. The shroud height was adjustable to allow for 5.1-cm 

(2-in), 20.3-cm (8-in), and 35.6-cm (14-in) perimeter bottom 

gaps with the floor (ground). A typical rectangular collector 

inlet with an area of 929 cm2

 (1 ft2) was located at the perimeter 

of the drill table. The dust collector-to-bailing airflow ratio was 

varied from 2:1, 3:1, and 4:1 at the different shroud gaps. 

 A second series of tests was also done at these same 

parameters with a reconfigured collector inlet hood that moved 

the inlet plenum closer to and around the drill hole. Figure 1 

shows the inlet hood design tested with a drill cuttings 

deflection plate facing the hole and the intake plenum opening 

above and around the deflection plate. 

Results

The laboratory dust collector test results show that the two 

most influential factors on collector dust capture were the 

collector-to-bailing airflow ratio and the shroud gap height with 

both inlet configurations (Figure 2). About a one order of magnitude increase in dust leakage or dust concentration was 

observed when the shroud gap height was increased from 5.1 to 

20.3 cm (2 to 8 in) with the conventional inlet configuration. 

The inlet hood improved drill dust collector system capture over 

the conventional inlet location, especially with large leakage 

breaches at the bottom of the shroud enclosure. Inlet hood dust 

reductions of 63% to 91% were measured for collector-tobailing airflow ratios of 3:1 to 4:1 at shroud gap heights of 20.3 

to 35.6 cm (8 to 14 in). 

Additional drill shroud enclosure field testing verified that a 

tight shroud enclosure minimized the amount of dust that 

escaped the collector inlet with either the conventional or inlet 

hood configuration. The test drill had an angle drill curtain 

shroud design that could be hydraulically raised and adjusted to 

tightly seal with nonparallel ground surfaces with respect to the 

drill deck angle. Dust concentrations adjacent to the shroud 

were 0.18 mg/m3

 with the conventional inlet and were slightly 

No. 512 October 2005 
Figure 1.CInlet hood design tested in laboratory. 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

5.1 cm 20.3 cm 35.6 cm 5.1 cm 20.3 cm 35.6 cm

Shroud Gap Height, cm

2:1 ratio

3:1 ratio

4:1 ratio

Baseline Inlet Hood

Figure 2.CDust escaping the laboratory drill shroud. 

reduced to 0.11 mg/m3

 with a retrofitted inlet hood. The 

collector-to-bailing airflow ratio changed from nearly 2.7:1 with 

the conventional inlet to about 2.1:1 with the inlet hood. Since 

airflow ratio is such a critical parameter in the 2:1 to 3:1 range, 

it is important to note that reestablishing the original airflow 

ratio to 2.7:1 (e.g., a larger fan) with the inlet hood would 

provide an even greater dust reduction. The functionality of the 

retrofitted inlet hood showed promise, but it requires some selfcleaning redesign modifications for long-term usage (more than 

a week). Nearly 1,524 m (5,000 ft) of drilling was done with 

the inlet hood until internal buildup of coarse dust impeded its 

operation. 

In conclusion, this research showed that a tight shroud is 

very beneficial for the drill dust collection system, while 

improvements for a leaky shroud could be achieved with 

collector-to-bailing airflow ratios $3:1 and/or by relocating the 

inlet. 

For More Information

For more information about drill dust controls, contact John 

A. Organiscak or Steven J. Page, NIOSH Pittsburgh Research 

Laboratory, Cochrans Mill Rd., P.O. Box 18070, Pittsburgh, PA 

15236B0070, phone: 412B386B6675 or 412B386B6669, respectively; fax: 412B386B4917; e-mail: JOrganiscak@cdc.gov or 

SJPage@cdc.gov, respectively. 

To receive other information about occupational safety and 

health topics, call 1B800B35BNIOSH (1B800B356B4674), or 

visit the NIOSH Website 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. 

DHHS (NIOSH) Publication No. 2006–108

PLAN VIEW

SIDE VIEW

Self-Cleaning

Deflection Plate

Drill Hole Hood Drill Steel

Deflector Plate

Mounting Bracket

15.2 cm

 30.5 cm

 5.1 cm

30.5 cm 61.0 cm

30.5 cm

30.5 cm

10.2 cm

10.2 cm

20.3 cm Rubber Seal