Ladder

A ladder is a vertical or inclined set of rungs or steps commonly used for climbing or descending. There are two types: rigid ladders that are self-supporting or that may be leaned against a vertical surface such as a wall, and rollable ladders, such as those made of rope or aluminium, that may be hung from the top. The vertical members of a rigid ladder are called stringers or rails (US) or stiles (UK). Rigid ladders are usually portable, but some types are permanently fixed to a structure, building, or equipment. They are commonly made of metal, wood, or fiberglass, but they have been known to be made of tough plastic.
Ladders are ancient tools and technology. A ladder is featured in a Mesolithic rock painting that is at least 10,000 years old, depicted in the Spider Caves in Valencia, Spain. The painting depicts two humans using a ladder to reach a wild honeybee nest to harvest honey. The ladder is depicted as long and flexible, possibly made out of some sort of grass.
Rigid ladders are available in many forms, such as:
Rigid ladders were originally made of wood, but in the 20th century aluminium became more common because of its lighter weight. Ladders with fiberglass stiles are used for working on or near overhead electrical wires, because fiberglass is an electrical insulator. Henry Quackenbush patented the extension ladder in 1867.
The most common injury made by ladder climbers is bruising from falling off a ladder, but bone fractures are common and head injuries are also likely, depending on the nature of the accident. Ladders can cause injury if they slip on the ground and fall. To avoid this, they tend to have plastic feet or base pads which increase friction with the ground. However, if the plastic is badly worn, the aluminium may contact the ground increasing the chance of an accident. Ladder stabilizers are also available to increase the ladder's grip on the ground. One of the first ladder stabilizers or ladder feet was offered in 1936 and today they are standard equipment on most large ladders.
A ladder standoff, or stay, is a device fitted to the top of a ladder to hold it away from the wall. This enables the ladder to clear overhanging obstacles, such as the eaves of a roof, and increases the safe working height for a given length of ladder because of the increased separation distance of the two contact points at the top of the ladder.
It has become increasingly common to provide anchor points on buildings to which the top rung of an extension ladder can be attached, especially for activities like window cleaning, especially if a fellow worker is not available for "footing" the ladder. Footing occurs when another worker stands on the lowest rung and so provides much greater stability to the ladder when being used. However footing a ladder should be seen as a last resort for a safe placement. The anchor point is usually a ring cemented into a slot in the brick wall to which the rungs of a ladder can be attached using rope for example, or a carabiner.
If a leaning ladder is placed at the wrong angle, the risk of a fall is greatly increased. The safest angle for a ladder is 75.5°; if it is too shallow, the bottom of the ladder is at risk of sliding, and if it is too steep, the ladder may fall backwards. This angle is achieved by following the 4 to 1 rule for a ladder placed on a vertical wall: for every four feet of vertical height, the ladder foot should move one foot from the wall. Both scenarios can cause significant injury, and are especially important in industries like construction, which require heavy use of ladders.
The European Union and the United Kingdom established a ladder certification system – ladder classes – for any ladders manufactured or sold in Europe. The certification classes apply solely to ladders that are portable such as stepladders and extension ladders and are broken down into three types of certification. Each ladder certification is colour-coded to indicate the amount of weight the ladder is designed to hold, the certification class and its use. The color of the safety label specifies the class and use.
A common superstition in English-speaking countries is that walking under a ladder is seen as bad luck. Some sources claim that this stems from the image of a ladder being propped up against a wall looking similar to a gallows, while others attribute it to ancient Egyptian traditions involving pyramids and triangles representing the trinity of the gods, and passing through the triangular shape made by a ladder against a wall was seen as desecration. Ladders have also been linked to the crucifixion of Christ, with author and scientist Charles Panati noting that many believe a ladder rested against the cross that Christ hung from, making it a symbol of wickedness, betrayal and death. In comedic children's media, the image of a character walking under a ladder being the cause or result of bad luck has become a common trope.