Seven percent of all injury-related global deaths in 2019 were attributed to drowning, relating to 236,000 lives claimed and the stark reality persists that incidents of drowning continue to occur within zones overseen by trained lifeguards. Some lifeguard training agencies advocate the use of specific scan techniques and patterns and the 10:20 protection rule is recommended by a variety of lifeguarding agencies. This study aimed to determine the effectiveness of the 10-second element of the 10:20 protection rule (referred to as the 10-second scan strategy) compared to a more natural scan strategy. Two 30-minute videos were developed capturing scripted and unscripted swimming pool hazards. Water safety experts were then employed to collectively review, identify, and achieve consensus on hazards. In a within-subject design, lifeguards (n = 25) were instructed to watch videos under two conditions (i.e., 10-second and natural scan conditions) and respond via whistle blow and vocal response. In the 10-second scan condition, lifeguards were instructed to use the 10:20 system of supervision and scan the zone every 10-seconds whilst supervising the pool. In the natural scan condition, lifeguards were told to follow a scan strategy that felt comfortable for them. The results demonstrated that there was no significant difference in the percentage of hazards detected in the 10-second scan condition compared to the natural scan condition. However, the results show that lifeguards were unable to execute the 10-second scan strategy (i.e., scanning the full zone every 10 seconds). While results show that hazard detection is similar in both conditions, lifeguards were not adhering to the 10-second scan and thus comparisons between the 10-second scan strategy and natural scanning are not possible. The key conclusion from this study is that it is not possible for lifeguards to scan the full zone every 10 seconds, despite explicit instructions to do so, and thus the 10:20 protection rule should be carefully considered if agencies are advocating it as an effective scanning strategy.