Working at heights is inherently dangerous, and as such workers who work at heights often benefit from a multi-dimensional approach to roof safety. In other words, rather than employing one single measure to guard safety several solutions are employed, from guardrail systems to rigorous training procedures.
A guardrail is a very effective physical measure protecting workers as they work from heights. Guardrails take many forms, however they all share a singular purpose, i.e. safeguarding the edge of the roof. Because of this physical barrier it becomes much less likely that a worker will slip off the roof. Also, where a guardrail is in place it is much less likely that objects will fall off the roof onto workers below (another common cause of injury.)
Fall arrest systems are another solution and are often installed in tandem with guardrail systems. Often, however, fall arrest systems are used where the installation of guardrail systems is impractical or difficult. Essentially, fall arrest systems are attached to workers so that if they slip off a roof, whilst working from heights, their fall is arrested and serious injury is avoided.
Whilst there are many physical measures that can be incorporated to protect workers from heights there are other measures you can employ too. Training is obviously critical, and all workers should be well trained in terms of how to work at heights and use systems like guardrail systems and fall arrest products.