Introduction In 2015, Thai Workmen’s Compensation Fund (TWCF) reported only 3 cases of Occupational Noise-induced Hearing Loss (ONIHL) among nearly 10 millions workers. Thai labour laws stated that hearing conservative programs (HCPs) was mandatory for noisy work stations. Baseline audiometric analysis must be performed using NIOSH criteria (SigTS). However, retest and referral to occupational physicians (OPs) for work-related assessment were usually not performed for Thai workers with 1 st 15 dB shift. Baseline audiometric analysis was not properly performed in many industries. For example, not all the previous test were considered in baseline revision or baseline may never be revised. All these leaded to under-reporting of ONIHL in Thailand.

Methods For remedy the situation, pilot study was conducted on 2539 workers among 17 chemical industries in eastern region of Thailand. 10 years audiometric results (2007–2016) were collected and analysed using SigTS and OSHA criteria (STS). Baseline revisions for each criteria were performed by OPs. The results were compared with those without baseline revision.

Result Without baseline revision, the accumulation, increasing of abnormalities over years could be the cause of unnecessary investigations. With proper baseline revisions, the incidence of SigTS, STS, and age corrected STS were only 19.27%, 10.21%, and 4.05% respectively. After age correction, only 2.61% had to visit OPs for work-related assessment each year.

Discussion STS with age correction and proper baseline revisions dramatically reduced total cost of investigations. This should be acceptable for industries in Thailand and other developping countries. Recommendation for Thai Ministry of Labour to revise HCPs regulations were:

• Baseline revision performed properly by OPs should be mandatory,

• Age corrected STS was the most cost–effective and practicable,

• All workers with worsening hearing must be referred to OPs and then TWCF, and

• Annually, HCPs installed industries must quantitatively evaluated ONIHL (diagnosed by OPs), SigTS, STS, and age corrected STS.