Development and 

Assessment of Controls 

Session

Assessing Controls

Efrem R. Reeves, PhD

Mining Hearing Loss Prevention Workshop

June 21-22, 2005

Pittsburgh Research Laboratory
Assessment of Engineering 

Noise Controls

What is the Assessment of 

Controls?

• Determining how well a control works

• Determining why a control does or 

doesn’t work
Assessment of Engineering 

Noise Controls

Why Assess Controls?

• Save Time

• Save Money

• Protect Workers
Assessment of Engineering 

Noise Controls

Controls Assessed:

• Motor Covers

• Absorptive Materials

• Windshields/Barriers

• Enclosed Environmental Cab
Motor Covers

Conveyor Belting

Fiberglass Blanket

Plexiglass
Motor Covers

Reduction

dB(A)

Bolter 1 (conveyor belt) 84.9 83.2 1.7

Bolter 2 (fiberglass) 77.3 76.9 0.4

Face Drill 1 (conveyor belt) 79.4 77.2 2.2

Face Drill 2 (fiberglass) 79.9 79.5 0.4

Face Drill 3 (plexiglass) 84.3 81.9 2.4

Motors

Uncontrolled 

Level dB(A)

Controlled 

Level dB(A)

- This application requires a barrier material

- Make sure sound level warrants treatment
Absorptive Material in Canopy
Absorptive Material in Canopy

Reduction

dB(A)

Bolter 2 97.4 97.3 0.1

Face Drill 1 99.1 99.3 -0.2

Face Drill 2 99.6 99.6 0

Face Drill 2 (no windshield) 100.3 100.1 0.2

Uncontrolled 

Level dB(A)

Controlled 

Canopy Level dB(A)
Absorptive Material in Lower 

Front of Cab
Absorptive Material in Lower 

Front of Cab

Reduction

dB(A)

Bolter 2 (drilling) 98.1 97.9 0.2

Bolter 2 (bolting) 99.9 99.9 0

Lower Cab 

Absorption

Uncontrolled 

Level dB(A)

Controlled 

Level dB(A)
Absorptive Material
Absorptive Material
Absorptive Material in Haul 

Truck

No Padding Padding Reduction

High Idle dB(A) dB(A) dB(A)

Truck 1 101.3 100.6 0.7

Truck 2 101.3 101.3 0

Truck 3 100.6 99.6 1
Noise Control Basics

• Placement of absorbing materials is 

VERY important
Noise Control Basics

• Special attention is required when 

attempting noise control underground
Windshields
Windshields

Reduction

dB(A)

Bolter 2 (Drilling) 98.5 97.9 0.6

Bolter 2 (Bolting) 101.2 99.9 1.3

Bolter 5 (Drilling) 100.6 99 1.6

Bolter 3 (Drilling) 99.2 96 3.2

Bolter 3 (Bolting) 105.7 102.5 3.2

Face Drill 1 101.7 99.3 2.4

Face Drill 2 100.3 99.6 0.7

Face Drill 3 97.1 95.3 1.8

Face Drill 4 (single boom) 94 91.9 2.1

Face Drill 4 (dual boom) 98.9 95.6 3.3

Face Drill 5 101.9 100.6 1.3

Windshields

Uncontrolled 

Level dB(A)

Controlled 

Level dB(A)
Windshields

Gaps greatly reduce the effectiveness of barriers
Windshield with Belting

Belting ‘cab’ not effective due to gaps between strips
Environmental Cab
Environmental Cab Sound 

Levels

Exterior Avg Interior Avg

High Idle dB(A) dB(A)

All Windows Open 99.9 96.9

Left Window Closed 98.2 93.8

Back and Left Window Closed 98.4 92.9

Back, Left, and Right Window Closed 99.9 89.1

All Windows Closed 100.3 77.7

An enclosed cab can be a very effective noise control
Conclusions

• Care should be taken to select the 

proper noise treatment for the 

situation

• Due to the operating environment 

and openness of the operator area, 

absorptive material was of limited 

benefit on the machines tested

• For maximum effectiveness all gaps 

should be eliminated from barriers
For more information

Efrem R. Reeves

Phone: 412-386-6158 Fax: 412-386-4865

efr2@cdc.gov

www.cdc.gov/niosh/mining

Pittsburgh Research Laboratory