A roofing toe board is one of the most basic pieces of safety equipment a roofer can use. A toe board is a long piece of 2 inch x 4 inch (a 2x4) wood nailed horizontally along a roof in various places.
Most roofers work in a variety of weather conditions, sometimes severe heat, and resist wearing an apparatus such as a safety harness. As a result of needing both an uncumbered work environment and the need to stay as cool as possible, roofers prefer the toe board due to its freeness of movement. If an accident happens and a roofer loses his/her footing, the 2x4 would stop the roofer from sliding down and/or off the roof.
More deaths occur in falls than for any other reason in the construction profession.
References
Toe board Wikipedia(Text) CC BY-SA