Ladder

An extension ladder
A ladder used for ceremonial purposes in Indonesia

A ladder is a vertical or inclined set of rungs or steps. There are two types: rigid ladders that can be leaned against a vertical surface such as a wall, and rope ladders that are 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.

Variations

Rigid ladders

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Rigid ladders were originally made of wood, but in the 20th century aluminium became more common because of its lighter weight.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.[4] Henry Quackenbush patented the extension ladder in 1867.[5]

Flexible ladders

Safety

Safe setup of a leaning ladder
Skid mark from a faulty ladder.

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 slip backwards owing to faulty base pads which usually fit into the ladder stiles. If badly worn, they can allow the aluminium to contact the ground rather than plastic or rubber, and so lower the friction with the ground. Ladder stabilizers are available that 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.[7]

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.

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. 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. Both scenarios can cause significant injury, and are especially important in industries like construction, which require heavy use of ladders.[8]

Ladder classes

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.

In the UK there are a number of British standards included in the three main ladder certifications relative to the particular ladder type. Relevant classifications include BS 1129:1990 (British) which applies to Timber Ladders and Steps; BS 2037:1994 (British) which applies to Metal and Aluminium Ladders and Steps and BS EN 131:1993 (European) which applies to both Timber and Aluminium Ladders and Steps.[10]

Uses

Historical usages

On the right hand page are types of ladders from the end of the 15th century in Germany.

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 kind of grass.[11]

See also

Notes

Citations
  1. ↑ "Diving Equipment Specialties". Techdivetools.com. Retrieved 2014-03-05.
  2. ↑ "Patent and Trademark Office Notices". Uspto.gov. Retrieved 2014-03-05.
  3. ↑ "Collapsible Platform For Maintenance Tasks - Patent 7204343". Docstoc.com. 2010-09-27. Retrieved 2014-03-05.
  4. ↑ "Workplace Solutions: Preventing Worker Deaths and Injuries from Contacting Overhead Power Lines with Metal Ladders". National Institute for Occupational Safety and Health. September 2007. Retrieved 16 January 2015.
  5. ↑ "Improved extension-ladder patent" (PDF). google.com. Retrieved 20 June 2012.
  6. ↑ Cutler, p 122
  7. ↑ "Metal Rubber Feet for Ladder Prevents Slipping" Popular Science, April 1936 article at bottom left of pg 499
  8. ↑ Simeonov, Peter; Hsiao, Hongwei; Powers, John (27 August 2013). "Ladder Safety: There’s an App for That". Retrieved 15 January 2015.
  9. ↑ "Safety in the selection and use of ladders" (PDF). Health & Safety Executive. Archived from the original (PDF) on November 18, 2012. Retrieved 17 May 2014.
  10. ↑ "British and European Ladder Certification Standards". Clow Group Ltd.
  11. ↑ Wilson, Bee (2004). The Hive: The Story Of The Honeybee. London, Great Britain: John Murray (Publishers). ISBN 0-7195-6598-7

References used

  • Cutler, Deborah W. and Thomas J. Cutler (2005). Dictionary of Naval Terms. Naval Institute Press, Annapolis, Maryland. ISBN 978-1-59114-150-1. 
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.