Accidents involving ladders are common, and can lead to broken bones and even death. These incidents can easily be avoided with a few simple steps, the most important of which is the angel the ladder is leaned at.
For a ladder that does not support itself, such as an extension ladder, it should lean at 75 degrees. This means the base of the ladder needs to be angled out one fourth of its height. For example, if the ladder is supported at a point 40 feet up, the base should be 10 feet out.
A ladder at a leaning angle over 75 degree is likely to tip backwards; if it must be used, the top should be tied off. A ladder that is at an angle less than 75 degrees is prone to slide out at the bottom. If the ladder is angled at 63 degrees or less there will be to much strain on the side rails and the ladder my break.
Many ladders come with stickers or other safety notices. Follow the ladders instructions on proper placement, as some specialized ladders have their own rules and necessary angels.