No. 533 September 2008 

Minimizing Respirable Dust Exposure in Enclosed Cabs 

by Maintaining Cab Integrity 

Objective 

To minimize the equipment operator’s respirable dust 

exposure in enclosed cabs of mobile equipment by installing cab filtration and pressurization systems and by keeping doors and windows closed. 

Background 

Enclosed cabs are used on mobile equipment to protect 

operators from health and safety hazards. The primary 

health concern is overexposure to respirable dust. Examples of such equipment in mining include drills, dozers, 

haul trucks, and other equipment. When equipment is new, 

the operator’s dust exposure is normally at acceptable 

levels. As the equipment ages and gaskets and seals deteriorate, the air quality inside an enclosed cab can reach a 

point where it is no longer at acceptable levels for the 

equipment operators. 

In an effort to improve the air quality in enclosed cabs 

of older mining equipment, NIOSH has been performing 

research to retrofit cabs with new filtration and pressurization systems. Over the past few years, this research has 

shown that retrofit systems can substantially improve the 

cab’s air quality back to safe and acceptable levels. However, this is only possible when a positive cab pressure is 

achieved and maintained. Thus, when a cab door or window is opened, the cab pressure drops to zero and the cab 

filtration and pressurization system is rendered ineffective. 

During a recent field study, the magnitude of this impact 

was noted when a drill operator repeatedly opened the cab 

door throughout the course of the drill cycle. Upon closer 

examination, it was determined that the cab door was 

being opened to manually guide the next drill steel into 

place each time an additional section of steel was needed 

to drill deeper holes. Figure 1.—Drill operator reaching out of cab door to guide 

new drill steel into place. 

Approach 

A recent test was performed to evaluate a new unidirectional flow cab filtration and pressurization system 

installed on an enclosed cab of a surface drill at a stone 

operation. During this test, instantaneous respirable dust 

monitors were placed inside the enclosed cab to evaluate 

the effectiveness of this new system. These monitors 

recorded the average respirable dust concentration every 

30 sec on the instrument’s internal datalogger. While performing this testing, it was noted that the drill operator 

repeatedly opened the cab door to manually guide a new 

drill steel into place each time an additional section was 

needed. During this evaluation, the operator was drilling 

holes to a depth that required the use of five steels. When 

the drill steel was advanced the entire length, the operator 

went through a series of tasks to remove the drill steel 

from the powered drive head, obtain another drill steel 

and swing it into place. At this point in the process, the 

drill operator opened the cab door, leaned out, and with 
 

his left arm manually guided the drill steel into the previous steel (Figure 1). When the new steel was completely 

threaded down tight into the previous steel, the drill operator closed the cab door and began drilling again. The total 

time to add a new drill steel was roughly 3 min. At 

approximately 2 min into the process, the drill operator 

would open the cab door to guide the next drill steel into 

place. The cab door was normally open somewhere 

between 30 and 45 sec each time this process took place 

before being closed again. Since no drilling was occurring 

and no dust cloud was visible as the cab door was opened, 

the impact to the drill operator’s respirable dust exposure 

was initially thought to be insignificant. 

0.08 

0.17 

0.03 

0.84 

0.39 

1.21 

0 0.5 1 1.5 

Day 3 

Day 2 

Day 1 

Closed Open 

 Figure 2.—Average respirable dust concentration (mg/m3 ) inside 

drill cab during periods with the cab door closed and open for 

3 days of testing. 

Results 

When the instantaneous respirable dust data from 

inside the enclosed cab were analyzed, a substantial 

increase in respirable dust concentrations was noted during 

the periods when the door was open. This increase was 

especially significant when one considers that drilling had 

ceased approximately 2 min before the door was opened. 

Figure 2 shows average concentrations for 3 days of testing for time periods when the cab door was closed and 

opened. The average concentration was 0.09 mg/m3 with 

the cab door closed and 0.81 mg/m3 with the door open. 

Despite no visible dust cloud during the time when the cab 

door was open, respirable dust concentrations inside the 

cab were nine times higher than when the door was closed. 

Additionally, once dust enters and coats the inside of the 

enclosed cab, it exposes the drill operator every time it is 

disturbed and becomes airborne, even with the cab door 

closed. 

The results of this testing indicate the significant 

impact of an open door or window on dust concentrations 

inside an enclosed cab. In operations where the cab door or 

window may be opened for longer time periods, especially 

in operations with higher outside dust concentrations or 

higher silica contents, the practice could have an even 

greater impact on the operator’s dust exposure. 

Recommendations 

Cab filtration and pressurization systems should be 

installed on enclosed cabs of all mining equipment to 

improve the air quality to the operator. In addition, every 

attempt should be made to keep cab doors and windows 

closed at all times in an effort to keep the cab pressurized 

and working properly. The only exception to opening a 

door should be when the equipment operator enters or 

exits the enclosed cab. For mining operations using drills 

that require the operator to manually guide drill steels into 

place, the drill manufacturer should be contacted to purchase systems that have been developed to provide for drill 

steel stabilization, eliminating the need for this task to be 

performed by the drill operator. 

For More Information 

For more information about reducing dust exposure in 

enclosed cabs, contact Andrew B. Cecala (412-386-6677, 

ACecala@cdc.gov) or John A. Organiscak (412-386-6675, 

JOrganiscak@cdc.gov), NIOSH Pittsburgh Research 

Laboratory, P.O. Box 18070, Pittsburgh, PA 15236-0070. 

Publications on dust control in the mining industry, 

including cab filtration and pressurization systems, can be 

downloaded from the NIOSH Mining Web site at http:// 

www.cdc.gov/niosh/mining/pubs/programareapubs9.htm. 

To receive NIOSH documents or for more information 

about occupational safety and health topics, contact: 

1-800-CDC-INFO (1-800-232-4636), 1-888-232-6348 

(TTY), e-mail: cdcinfo@cdc.gov, or visit the NIOSH 

Web site at http://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. 2008–147