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This study evaluated the psychometric validity and clinical utility of the 12-item General Health Questionnaire (GHQ-12) in isolated, confined and unusual or extreme (ICUE) work environments in South Africa. Two occupational health surveillance cohorts (N = 730 and N = 128) representing diverse occupational fields completed the GHQ-12 together with validated measures of common mental disorders, psychological resilience, emotional wellbeing and mental toughness. Confirmatory factor analyses supported a bifactor model comprising a strong general factor with minimal unique variance attributable to the positive and negative item subfactors. Internal consistency was high across samples. The GHQ-12 total scores correlated positively with depression, anxiety and adjustment disorder symptoms, and negatively with psychological resilience, emotional wellbeing and mental toughness, supporting convergent validity. Test-retest reliability was moderately strong, with a minority showing marked deterioration of mental health under more stressful operational conditions, indicating the tool's potential sensitivity to environmental stressors. The GHQ-12 total scores differentiated between individuals with and without common mental disorders, and receiver operating characteristic analyses indicated acceptable sensitivity and specificity at optimal thresholds. Introducing a 'grey-zone' approach with lower and upper thresholds enhanced its practical application for surveillance and triage, by improving risk identification and decision-making for occupational health practitioners.

This study provides the first large-scale evaluation of the GHQ-12 in ICUE occupational environments in southern Africa. By combining psychometric evaluation with a clinically oriented grey-zone approach, it offers evidence to support how brief mental health tools can be applied to high-risk workplaces such as offshore vessels, submarines and polar research stations.