Page 38 - Summer 2006

reduce worker hand-transmitted vibration exposure. Workers should not be subjected to hand-transmitted vibra- tion exposures above the DELV. The DEAV and DELV values have generally been accepted by medical experts, scientists, and engineers in governmental agencies, research institu-
2
tions, and industry in the USA and other countries. When
they are achieved, they will reduce the potential for the devel- opment of symptoms related to HAVS among workers exposed to hand-transmitted vibration.
Significant improvements in measurement and analysis instrumentation, miniature and subminiature accelerome- ters, and medical diagnostic and assessment protocols have been introduced since 1986 when ANSI S3.34 was first pub- lished. In response to these improvements, the publication of a revised ISO 5349 in 2001, and the introduction of the EU Human Vibration Directive, ANSI Working Group S2.39 developed the revision to ANSI S3.34, which has been desig-
2
Significant elements of ANSI S2.70
ANSI S2.70 specifies the use of the hand-arm vibration
measurement procedures outlined in ISO 5349, Parts 1 and
2,4,5
2 . The single-axis r.m.s. ISO frequency-weighted accelera-
tion values are measured in three mutually orthogonal axes of vibration. The vibration total value, ahv(rms), is then obtained from:
(1)
where ahw(rms)x, ahw(rms)y, and ahw(rms)z are the measured single- axis r.m.s. ISO frequency-weighted acceleration values in the x, y, and z directions, respectively. If multiple vibration expo- sure events are experienced during a work day, the overall vibration total value, ahv(rms), is obtained from:
Figure 2 shows a plot of Dy as a function of the daily vibration exposure value, A(8).
Importance of ANSI S2.70
DEAV to reduce health risks.
ANSI S2.70 defines a value of A(8) equal to 5.0 m/s2 as the
2
Daily Exposure Limit Value (DELV). Workers who are
exposed to hand-transmitted vibration at or above this level are expected to have a high health risk. “High health risk is defined as the dose of hand-transmitted vibration exposure sufficient to produce abnormal signs, symptoms, and laboratory findings in the vascular, bone or joint, neurological, or muscular systems of the hands and arms in a high proportion of exposed individu- als.”2 ANSI S2.70 recommends that workers not be exposed to hand-transmitted vibration above the DELV.
The vibration total values, ahv(DEAV) and ahv(DELV), for a daily vibration exposure time, Tv, other than 8 hours that are associated with the DEAV and the DELV are given by:
DEAV: 􏰀8 T=200
ahv(DELV) = 5.0 or v a2 (4)
DELV: 􏰀8orT=50
ahv(DEAV) = 2.5 T v 2 (5)
v
is greater than 15 minutes and less than 12 hours in a 24-hour period. Figure 1 shows plots of the ahv(DEAV) and ahv(DELV) values for time periods other than 8 hours. The region between the two curves is referred to as the health risk zone. The region above ahv(DELV) is referred to as the high health risk zone.
The latency period or time in years, Dy, before vascular symptoms associated with HAVS are expected to first appear in ten percent of a worker population exposed to work-relat- ed hand-transmitted vibration can be estimated when the daily vibration exposure value, A(8), is known. Dy can be estimated from2,4:
nated as ANSI S2.70-2006.
T hv(DEL V) v
where T v
ahv(DEAV)
ahv(rms) =
Tv i=1
2hv(rms)i i (2)
31.8 1n A(8)1.06
(6)
􏰀 􏰁(a T)
where ahv(rms)i is the vibration total value of the ith operation, Ti is time duration in hours of the ith operation, n is the total number of operations, and Tv is total time in hours associat- ed with the n operations. Finally, the daily vibration exposure value, A(8), standardized to an 8-hour reference period, is obtained from:
(3)
ANSI S2.70 defines a value of A(8) equal to 2.5 m/s2 as
2
the Daily Exposure Action Value (DEAV). The DEAV repre-
sents the health risk threshold to hand-transmitted vibration. “Health risk threshold is defined as the dose of hand-trans- mitted vibration exposure sufficient to produce abnormal signs, symptoms, and laboratory findings in the vascular, bone or joint, neurological, or muscular systems of the hands and arms in some exposed individuals.”2 ANSI S2.70 recom- mends that a program be designed to reduce worker expo- sure to hand-transmitted vibration when A(8) exceeds the
Dy =
Fig. 1. Plots of the ahv(DEAV) and ahv(DELV) values for vibration exposure times other than 8 hours.
A (8) = ahv(rms) 􏰀Tv To
where To is the reference period of 8 h.
36 Acoustics Today, July 2006