The safest angle for a ladder will depend on two things: the jurisdiction and the type of ladder in question. For the purpose of answering your question, we will discuss portable extension ladders. Why? Well, because if you get the ladder angle wrong with one of those, bad things can happen:
- Angle is too step? The ladder can fall right back over you, or slide sideways during use. Belushi could walk away from his fall off a portable ladder in Animal House. In reality, he would have been seriously if not fatally injured.
- Angle too shallow? The bottom kicks out and down you go.
- Unsecured? Not safe in any circumstance.
Another thing that bears mentioning: extension ladders are not work platforms. They are for getting up and onto a work area.
Now, to answer the question more directly, let's go over some relevant legislation, standards, and codes:
- NIOSH puts a safe working angle at 75.5 degrees for an extension ladder on a work site. They also have an app that will allow you to find the correct angle for the ladder you are using.
- OSHA says, “When a ladder is leaned against a wall, the bottom of the ladder should be one-quart
er of the ladder’s working length away from the wall.”
- The Canadian Centre for Occupational Health and Safety lists all the jurisdictional information available across Canada. For example, in Alberta, 15 separate sections of the OHS Act cover ladder safety.
- Another Standards organization, the American Ladder Institute, has links to all of the OSHA information regarding ladders. They also offer free web-based training.
- And last, National Safety Inc. speaks to extension ladder angles using the 4 to 1 ladder rule, which means that for every 4 feet you go up, the ladder must be 1 foot out from the base of the wall (so, a ladder that is 20 feet high needs to be 5 feet out from the base of the wall).
Ladder use is common, and ladder safety is an extensive subject. Answering the question about safe angles for an extension ladder barley touches the depths of safe ladder work. While angles are a critical factor, they are simply one of many critical factors for ensuring safety while using ladders. Always remember the critical nature of securing the top of a ladder and anchoring the base.