The American National Standards Institute defines testing procedures that classify ladders into the following grades1 (capacity includes the weight not just of the person but also of any paint, tools, etc.):
| Grade | Capacity (pounds) |
Comment |
|---|---|---|
| IAA | 375 | Special Duty. |
| IA | 300 | Extra Heavy Duty. |
| I | 250 | Heavy Duty. |
| II | 225 | Medium Duty. For light commercial use. |
| III | 200 | Light Duty. For household use. |
The Canadian Standards Association defines the following grades:
| Grade | Capacity (pounds) |
Comment |
|---|---|---|
| I | 250 | |
| II | 225 | |
| III | 200 |
Ladders are usually made of:
Extension ladders consist of telescoping sections. The rails of the top section fit inside the rails of the bottom section and are held to them by brackets at the top of the bottom section. The top section is usually pulled up by a rope; a ratcheting device that engages the rungs of the bottom section prevents the top section from sliding back down when in use.
Most extension ladders have two sections, but a few very long ladders (60 feet) have three sections. In the United States and Canada, extension ladders are sized by the sum of the lengths of the sections. Sizes of 2-section ladders begin at 16 feet (2 sections each 8 feet long) and progress in 4-foot increments to 48 feet.
Because the sections must overlap, the maximum extended length of an extension ladder is less than its size. For example, a 24-foot extension ladder will consist of two sections each 12 feet long, but the maximum extended length will be 21 feet, because the sections overlap by no less than 1½ feet when the ladder is at maximum extension. The longer the sections, the greater the built-in overlap. As a result, the extended length of ladders 28′ and shorter is 3′ less than their size, those from 32′ to 36′ are 4′ shorter than their size, and 40′, 44′, and 48′ ladders are 5 feet shorter than their size.
In Europe, extension ladders are often sized by the number of sections times the number of rungs on each section, for example, “2×16”. The length of a section and the maximum extended length will be found in the manufacturer's specifications; differences between sizes vary from manufacturer to manufacturer.
Extension ladders are intended to be used at an angle of 75.5 degrees, which is equivalent to the length of the ladder being 4 times the horizontal distance between the point of support and the foot of the ladder.
The form below can be used to estimate the required extension ladder size. If the ladder's point of support is the edge of a roof, deck or other platform which a worker is going to climb out on from the ladder, the ladder must extend beyond the point of support by something like 3 feet (1 meter).
After entering a height, click anywhere outside the boxes to calculate.
© iStockphoto,com/Denis Sauvageau
In orchards, a type of ladder is used which gets its stability on rough ground by having three instead of four feet. They are often called tripod ladders. The rails are not parallel, but flare toward the base to increase stability, while allowing a narrower top that fits among a tree's branches. The third foot is a pole hinged to the top of the ladder. This type of ladder is commercially available in heights from 4 to 16 feet.
In use, the ladder is placed with the pole side facing the trunk of the tree, and the feet sunk into the earth. Unlike a stepladder, there is nothing to maintain the angle between the rails and pole. These ladders should never be used on hard surfaces; they will collapse.
1. ANSI Standard A14.10-2000.
European Standard EN131.
Advice on the safe use of orchard ladders:
www.cdc.gov/nasd/docs/d001701-d001800/d001722/d001722.html
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Last revised: 8 November 2003.