The design of offshore installations can increase risks to safety of workers building and using these installations. In this research, we aim to investigate how differences between designers influence the quality of designers' judgement, and how the quality of judgement influences installation safety. In the main phase of the research, we will assess individual differences between designers, quality of designers' judgements, and other factors in a sample of over 300 designers. We will assess factors that indicate designers' judgement quality (memory lapses, risky decision-taking). We will do this by asking designers to complete brief assessments several times per day over four periods of one working week. Designers will make these assessments on palmtop computers. We expect to gain over 15,000 such assessments. In this way, the indicator of judgement quality between designers takes into account periodic variations in performance, rather than relying on a single-shot measurement that could be inaccurate.We will then relate indicators of judgement quality, and designers' individual differences, to the safety of the designs they were working on during the period of the study.