Human vibration

Vibration transmitted to a person is evaluated with a measurement chain deliberately parallel to a sound level meter’s: the acceleration is frequency-weighted to reflect how the body responds at each frequency, reduced to a weighted r.m.s. value or a dose, combined across axes, and normalised to a daily exposure that regulation can act on. Four pages cover it: the general chain, the special case that breaks it, what a seat does to the vibration it passes on, and whether the instrument doing the measuring is entitled to be believed.

Human Vibration is the general chain. It covers the whole-body and hand-arm frequency weightings of ISO 8041-1, the weighted r.m.s. acceleration and the running and dose measures of ISO 2631-1 (MTVV, VDV, MSDV, crest factor) that flag shocks a plain r.m.s. would hide, the direction-independent Wm weighting that ISO 2631-2 prescribes for building occupants on every axis, the hand-arm vibration total value and daily exposure A(8) of ISO 5349-1/-2, and the exposure action and limit values of Directive 2002/44/EC that make A(8) legally meaningful.

Multiple-shock whole-body vibration (ISO 2631-5) handles exposures the r.m.s. philosophy underestimates: repeated mechanical shocks from off-road vehicles, high-speed craft or earth-moving machinery, which load the lumbar spine far beyond what their energy average suggests. ISO 2631-5:2018 models the seat-to-spine transfer explicitly, accumulates a dose from the response peaks, and converts it into compressive stress on the vertebral endplates and a probability of lumbar injury over a working life.

Use the ISO 2631-1 metrics first, and let two numbers decide when to move on. A crest factor above 9 says the basic weighted r.m.s. method is no longer adequate for that record, which is the ISO 2631-1 trigger for reaching for the running and dose measures. A **band-limited vertical peak acceleration above 9.81 m/s² (1 g, the free-fall threshold) puts the exposure in ISO 2631-5’s clause 5 regime, the severe shocks with possible loss of contact with the seat that this library implements, rather than in its Annex A finite-element model for exposures in which the occupant stays seated. The measurement front-end (weighting filters, band analysis) is shared with the core signal analysis section.

• Human Vibration: ISO 8041-1 weightings, ISO 2631-1 r.m.s. and dose measures, ISO 5349 daily exposure A(8) and the Directive 2002/44/EC values.
• Multiple-shock whole-body vibration (ISO 2631-5): the spinal-response model, acceleration dose and probability of lumbar injury.
• What a seat does to the vibration (ISO 10326-1): the SEAT factor of a laboratory seat test, the correction to the input the test intended, and the transmissibility at resonance of the damping test.
• Verifying a human-vibration meter (ISO 8041-1): the tolerance band around each frequency weighting, the characteristic phase deviation, the running r.m.s. decay and the saw-tooth burst indications a conforming meter has to reproduce, and the personal vibration exposure meter of ISO 8041-2, graded with the same burst tables.

• the clauses that are arithmetic

  A meter is graded on the clauses that can be computed. The tolerance tables of ISO 8041-1 are implemented, and so is every other criterion of it that is arithmetic: the band-limiting stage on its own, the characteristic phase deviation, the running r.m.s. decay times and the 228 saw-tooth burst indications the standard prints, which is what meter verification is about. The design and type-testing clauses of that standard, from indication and linearity to the environmental tests, are laboratory measurements on hardware and stay outside: a pass on any of these is a necessary condition for conformity, not a certificate of it.

• Building vibration stops at the weighting. Of ISO 2631-2 the library implements the direction-independent Wm curve and nothing else, and that is closer to the standard than it looks: the 2003 edition deliberately deleted its predecessor’s guidance values, so there are no acceptable magnitudes for building vibration to compare against. A reader looking for a limit will not find one here, and will not find one in the standard either.

• Of ISO 2631-5, the clause 5 model only. The Annex A finite-element model for less severe seated exposures is distributed separately by ISO and is not implemented, which is what makes the 1 g delineation above a routing decision rather than a preference.

• And the verdict stops at the directive itself. An A(8) is assessed against the action and limit values of Directive 2002/44/EC (each marked exceeded or not, the exposure zone named, and a PASS/FAIL verdict issued against the limit value) but the library applies no national transposition of the directive, and the conclusion of a workplace risk assessment is not a number this section produces.