An Evaluation of Concrete Saw Blades for Noise Reduction
Susan Shepherd ScD, M. Abbas Virji ScD and Susan Woskie PhD CIH University of Massachusetts Lowell
This study was funded by the National Institute for Occupational Safety and Health (NIOSH) through a grant to the Center to Protect Workers Rights (CPWR)
Noise exposure levels in construction
Large equipment, but also hand held tools Concrete cutter: 105 dBA1 Cut-off saw: dBA; peak: 118 dBA2 Gas saw, carbide blade: 95 dBA (5 ft.) est. source: 109 dBA3
1. Methner etal. JOEH 15(11), 2000 2. OSH Service, Dept of Labor, New Zealand, 2002 3. Greenspan etal, Appl Occ Env Hyg, 10(1), 1995
Hearing Loss in Construction
90% of SMW ages 50-59 lost >30dB @ 4k Hz (Byggahlsan study)1 49% of 5000 construction workers studied by Workers Comp Bd of BC1
1. Schneider etal STAR Construction Health & Safety, 1995

Experimental Methods

Personal noise dosimeter (Larson Davis 706 Type 2) 3 Area noise dosimeters 1 Sound level meter (Larson Davis Type 1) with octave band analysis 5 saw blades Reinforced concrete pipe Each worker uses all five blades (wet and dry) Personal dust exposures (Thermo pDR w/cyclone)
Factors contributing to noise

Saw motor Blade

Configuration Speed Material
Material being cut Work practice Environment

Concrete Chop Saws

Gas powered circular saw used to cut concrete pipe, paving & curb stones, sidewalk Reduction of noise via blade design proposed

Stihl TS 400: 4.4 HP

Makita DPC 7311: 5.6 HP

Partner K700: 4.8 HP

Saw motor noise
Saw Stihl 400 Makita DPC 7311 Partner K700 dBZ 87.4 91.7 NT

Test with SLM @ 16 in.

Octave Band Analysis Stihl motor
60.0 50.0 40.16 31.8000 16000

Frequency, Hz

Five blades
1. 2. 3. 4. 5. Diamond regular Carbide regular Carbide holes blades Carbide turbo Diamond noise-reducing (NR)

Diamond Regular Blade

24 segments 13 7/8 in. diameter Gullet depth: 21 mm Gullet width: 3 mm 7 mm Relief: 6 mm diameter

Carbide blade

24 segments 13 1/4 in. diameter Gullet depth: 15 mm Gullet width: 2 mm 3 mm Relief: 5 mm diameter
Noise reducing diamond blade
24 segments 13 5/8 in. diameter Gullet depth: 25 mm Gullet width: 3 mm 5 mm Relief: 6 mm diameter Smileys: 32 mm diam

Carbide Turbo Blade

Unsegmented blade 13 3/8 in. diameter No gullets teeth space: 3 mm

Carbide holes blade

24 segments 13 7/8 in. diameter Gullet depth: 22 mm (10 mm x 15 mm) Gullet width: 3 mm 6 mm Relief and holes: 6 mm diameter

100 Left Center Right

110 Lzeq 103 Left Center Right

102 100

Left Center Right

Carbide Regular Blade

110 L z eq Left Center Right

NR Diamond Blade

L z eq

Noise Levels

Preliminary Results
Free-running Saw motor only (Stihl 400) Carbide Regular Carbide Turbo 89 dBA 107 dBA 100 dBA Cutting concrete pipe NA 105 dBA 101 dBA 104 dBA 106 dBA

Carbide Hole 110 dBA Blade Diamond Regular 113 dBA
Noise Levels by Blade Personal Dosimeter (LAeq)
NR diamond Carbide regular Turbo carbide Carbide holes blade Diamond regular
Not statistically different.
105.8 dBA 106.1 dBA 105.8 dBA 105.1 dBA 105.5 dBA

What is LAeq?

2 p (t ) 1 Leq = 10 Log10 T 2 dt dB T po 1 T2
P(t) = instantaneous frequency weighted (A or C), sound pressure in pascals Po = reference sound pressure, 20 Pa T = measurement period (Run Time or time history period, T = T2 T1

People

Statistical difference between individual workers average LAeq. Due to problems with the saws, only 4 out of 15 people completed all 10 trials (range of n=3 to 10 per person) Four person: 105.0 dBA, 106.0 dBA, 107.5 dBA, and 102.0 dBA Overall range of LAeq: 97.8 dBA to 111.2 dBA
Octave Band Analysis All blades - Partner

Person 9

80.0 dBZ
C. Reg D. Reg C. Hole C. Turbo

40.16 31.Frequency

Octave Band Analysis All blades - Stihl

Person 1

110.0 100.0
C. Reg C. Hole C. Turbo D. Reg D. NR

40.16 31.Frequency, Hz

Work practices
Dependent on saw maintenance Choke open Tightening blade (blade shim) Sawing direction Depth of cut Height of worker (vs. height of cutting) Position while cutting

Bystander exposure

If Leq at 1.5 feet (operator ear) is 105 dBA:
90 dBA is at 8 feet 85 dBA is at 15 feet
If Leq at the operator is 111 dBA:
90 dBA is at 16 feet 85 dBA is at 29 feet
Not considering reverberation in a concrete building site

Administrative Controls

A 105 dBA task:
can be performed for one hour and still be under the 90 dBA TWA Requires hearing protection with an NRR of 44

Conclusions

Not ready to recommend a saw blade design to control noise Saw maintenance is important to blade stability, which may help to control noise Hearing protection for all workers in the area is necessary.

Further work

Look more closely at work practices that may decrease noise exposure Relate rpm measurements to noise output