The Validity of LNT Model & its Impact on Derivation of Exposure Limits - Recording 23/02/24

Winner - 2023 AIOH Conference 3M Best Paper Award.

This paper discusses the controversy over the use of the linear non-threshold (LNT) model and presents the case for the existence of a threshold of effect for both asbestos and crystalline silica. The existence of threshold affect does not support the suggested need to further reduce the current OELs for these substances and others.


Ian Firth
Ian has over 45 years work experience, 34 of them with a multi-national mining and minerals company. A quarter of his work experience is in environmental sciences and the rest in occupational hygiene. Occupational hygiene work has involved workplace environment assessment (dust, fume, noise, etc) in hard rock mining settings in PNG and Indonesia, and in smelting in the zinc/lead and aluminium industries.

During the last 15 years of his career with Rio Tinto, he was the corporate Principal Adviser – Occupational Health, conducting audits and reviews of world-wide operations and providing coaching and training to working hygienists as well as standards and occupational hygiene guidance development. For the past 8 years he has been the Principal Consultant and Director of IC Firth OHs Solutions Pty Ltd.

Ian has a MSc in Applied Biology (toxicology) and is a Fellow of the Australian Institute of Occupational Hygienists (AIOH) as well as being a Certified Occupational Hygienist (COH)®. He was also chairperson of the AIOH Workplace Exposure Assessment Committee for 22 years. He has been involved in the authorship of a number of AIOH publications covering occupational hygiene risk assessment, workplace monitoring and statistics, and heat stress.