Overview
ISO/DTS 1999 - Acoustics - Estimation of noise-induced hearing loss is a technical specification from ISO/TC 43 that provides a statistical framework for predicting the effects of noise exposure on population hearing. The document (fourth edition, replacing ISO 1999:2013) links measured or estimated noise exposure to expected shifts in hearing threshold levels, using age-related hearing threshold databases (HTLA) and a defined effect of noise (N) metric. It also introduces a kurtosis-based adjustment to account for impulse/impact noise.
Key topics
- Statistical prediction of hearing threshold shifts: Procedures to estimate hearing threshold levels for noise-exposed populations versus comparable non-exposed populations.
- Databases for HTLA: Two main database types (Database A and Database B) give reference hearing threshold levels associated with age; these are used to separate age-related and noise-induced effects.
- Effect of noise (N): Tabulated values and interpolation methods are provided to quantify the noise component of hearing change. The document derives N from combined hearing threshold relationships using the formula:
- H' = H + N – (H × N / 120)
- Rearranged: N = (H' – H) / (1 – H/120)
(H = age-related component, H' = observed threshold)
- Measurement and description of noise exposure: Guidance on how noise exposure should be characterized for prediction calculations (see Clause 5).
- Kurtosis adjustment (Annex E): An adjustment to the exposure metric to improve predictions for noise containing substantial impulse/impact components, using waveform kurtosis.
- Assessment and risk estimation: Methods to calculate hearing loss, hearing impairment, and risk of impairment (Clauses 6–7 and Annexes C–D).
- Informative annexes: Examples, derivations and worked calculations (Annexes A–F) to support implementation.
Applications
ISO/DTS 1999 is intended for use in:
- Occupational health and safety: Designing hearing conservation programs, setting medical surveillance priorities, and evaluating long-term risk from workplace noise.
- Audiology and epidemiology research: Estimating population-level noise-induced hearing loss (NIHL) and comparing exposed vs non-exposed cohorts.
- Acoustical consulting and industrial hygiene: Assessing the long-term hearing consequences of measured noise exposures, including complex impulse noise environments.
- Regulatory and standards bodies: Informing policy, exposure criteria, and normative limits for noise control.
Who should use it
Occupational hygienists, audiologists, hearing conservation program managers, acoustical engineers, researchers, and regulatory agencies involved in noise exposure assessment and NIHL risk estimation.
Related standards
- Previous edition: ISO 1999:2013 (cancelled and replaced by this edition).
- Prepared by ISO/TC 43 (Acoustics) - consult national member bodies or ISO for related acoustics standards and implementation guidance.