Human Response, Criteria and Standards
This domain tests the subjective scales used to characterise noise and vibration, and the exposure criteria built on them.
Core rules
- Equal-loudness contours (ISO 226): the phon level of a tone equals the SPL of an equally loud 1 kHz tone. Loudness in sones is anchored so that 1 sone = 40 phon, and a 10 phon increase roughly doubles loudness.
- A-weighting approximates the inverse of the 40-phon contour, so it under-represents low-frequency noise and is less appropriate at very high levels or for strong tones.
- Community criteria are typically expressed as Lden and Lnight; sleep disturbance guidance is oriented to night-time levels around 40 dB outdoors.
- Whole-body vibration (ISO 2631-1) uses frequency-weighted RMS acceleration a_w and daily exposure A(8) = a_w√(T/8). Action value 0.5 m/s², limit value 1.15 m/s².
- Hand-arm vibration (ISO 5349-1) uses the Wh weighting: action value 2.5 m/s² A(8), limit 5 m/s² A(8).
Worked example
A worker uses a tool producing a_w = 1.0 m/s² for 4 hours. A(8) = 1.0 × √(4/8) = 0.71 m/s². That exceeds the 0.5 m/s² action value, so exposure must be controlled and health surveillance considered, but it remains below the 1.15 m/s² limit value.
Traps that cost marks
- Confusing phon and sone: one is a level scale, the other a ratio scale.
- Treating A-weighting as a loudness model for all levels and spectra.
- Adding vibration exposures arithmetically rather than as the square root of the sum of squares.
- Comparing a partial-body or single-axis value against a criterion expressed for a different axis weighting or exposure duration.