Vibrometry - Fundamentals and Assessment Tools for Occupational Ergonomics - page 660

m/s 2

20
16
12.5
10
8.0
6.3
5.0
4.0
3.15
2.5
2.0
1.6
1.25
1.0
0.8
0.63
0.50
0.40
0.315
0.25
0.20
0.16
0.125
0.10

1.6

1.0
x gn

0.63

0.4

0.25

1 min
16 min
25 min

0.16

0.1

1h

0.063

2.5h

TO OBTAIN
−

0.04

“EXPOSURE LIMITS”: MULTIPLY
ACCELERATION VALUES BY 2(6 dB
HIGHER);
−

4h

0.025

“REDUCED COMFORT BOUNDARY” :
DIVIDE ACCELERATION VALUES BY
3.15 (10 dB LOWER).

8h

16 h

0.016

24 h

0.016 0.4 0.5 0.63 0.8 1.0 1.25 1.6 2.0 2.5 3.15

4.0 5.0 6.3 8.0 10 12.5 16 20 25 31.5 40 50 63 80

Frequency or Center Frequency of Third-Octave Band, Hz

FIGURE 33.7 (FDP) Whole-body vibration curves separately used for X, Yaxes rms acceleration evaluations. (ANSI
S3.18, ISO 2631, EU)

standard is exceeded if one or more spectral peaks in any of the axes touches or exceeds one or more of
the exposure time dependent curves; the ACGIH-TLV for HAVuses the same “shape” weighted curve but
requires that each axis yield a numerical weighted sum, each of which is next compared to the acceptable
values of HAV daily exposure given in Table 33.1. The EU standard also requires that each of these
numerical weighted values or their weighted sum be compared to the 2.5 meters

sec. “action
level.” Notice that the format of Figure 33.8 is similar to the formats of Figure 33.6 and Figure 33.7,
where the abscissa is vibration frequency, in 1

sec.

/ /

3 octave bands, from 5.6 to 1250 Hz and the ordinate
is vibration intensity in acceleration. All standards use the HAV measurement coordinate system pre-
viously shown in Figure 33.2 with the “basicentric system” the method of choice. Except for NIOSH
#89-106, all of the above standards use this same “elbow shaped” weighting given in Figure 33.8.
The NIOSH standard is an interim standard without stating any acceptable acceleration level limit at
any frequency; this standard asks for each axis that: (1) weighted HAV acceleration values from 5.6 to
1250 Hz be calculated, (2) unweighted acceleration values from 5.6 to 5000 Hz be calculated, and (3)
the weighted and unweighted be compared in view of the severity of the prevalence of the hand-arm
vibration syndrome (HAVS) determined by using the tool(s) from whence these acceleration measure-
ments were made. NIOSH has chosen to issue this interim standard because there is an anomaly in
the other HAV standards, namely that the HAV weighting network shown in Figure 34.4 was originally
developed using older vibrating tool types commonly found in the workplace. Over the last few years,
some very high speed vibrating hand tools have been introduced, some of which have spectral peaks
extending to 5000 Hz and above. Current standards end at 1250 Hz, and hence in a few instances the
current standards would rule these very high-speed tools as acceptable when that may not be the case.
NIOSH has chosen to keep their interim standard, until this anomaly is resolved.

/