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We have undertaken the first study to determine, in an operational scenario, the visual acuity required by beach lifeguards in order to identify a human head at the outer edge of a patrolled area of 300 m out to sea. The required visual acuity as determined by the angle subtended by a human head at this distance would be 6/17, but as a result of location and detection factors we hypothesised that it would have to be better than this.
The experiment received ethical approval and 21 beach lifeguards (16 men, 15 women, all under 35 years) gave their consent to participate. After eye tests to ensure …
Competing interests: None.
Funding: This work was funded by the Royal National Lifeboat Institution.