A zip-line, zip line, zip-wire, flying fox, or death slide is a pulley suspended on a cable, usually made of stainless steel, mounted on a slope. It is designed to enable cargo or a person propelled by gravity to travel from the top to the bottom of the inclined cable by holding on to, or being attached to, the freely moving pulley. It has been described as essentially a Tyrolean traverse that engages gravity to assist its speed of movement. Its use is not confined to adventure sport, recreation, or tourism, although modern-day usage tends to favor those meanings.
Ropeways or aerial cables have been used as a method of transport in some mountainous countries for more than 2,000 years, possibly starting in China, India and Japan as early as 250 BC, remaining in use in some remote areas in China such as Nujiang (Salween) valley in Yunnan as late as 2015 before being replaced by bridges. Not all of these structures were assisted by gravity, so not all fitted the definition of the zip-line.
Various technological advances in Europe in the Middle Ages improved the power-line's ropeways, some of which were still assisted by gravity.
The first recorded use of the zip-line as a form of entertainment was possibly in 1739, when Robert Cadman, a steeplejack and ropeslider, died when descending from Shrewsbury's St Mary's Church when his rope snapped. In literature, one appears in The Invisible Man (published 1897) by H. G. Wells as part of a Whit Monday fair and referred to as "an inclined strong".
Some sources attribute the development of zip-lines used today as a vacation activity to the Tyrolean traverses developed for mountaineering purposes.
In the Australian outback, zip-lines were sometimes used for delivering necessities to people working in or on the other side of a valley, and they may have been used in conflicts by Australian troops to deliver food, mail and even ammunition to forward positions.
Yungas, Bolivia, features a system of zip-lines used for transporting harvested crops, mainly coca, across a valley 200 m below. They can also be seen in the Ladakh region of India.
In recent years, there has been renewed interest in the use of aerial ropeways for transporting cargo, partly due to their low energy requirements and environmental impact. Gravity-fed types, i.e. zip-lines, have been built in Nepal, Latin America and India.
Ziplines have also been used as a means of transporting items in Australian regions in the past. These may include ammunition, weapons, tools, food, and mail.
Zip-lines may be designed for children's play and found on some adventure playgrounds. Inclines are fairly shallow and so the speeds kept relatively low, negating the need for a means of stopping. The term "flying fox" is commonly used in reference to such a small-scale zip-line in Australia, New Zealand, and Scotland. With playground equipment, the pulleys are fixed to the cable, the user typically hanging onto a handgrip underneath, but occasionally including a seat or a safety strap. Return of the grip or seat is usually done by simply pushing or pulling it via a short wire back to the top of the hill on foot.
Longer and higher rides are often used as a means of accessing remote areas, such as a rainforest canopy. In the 1970s, wildlife biologists set up zip-lines as a way to study and explore the dense rainforests of Costa Rica without disturbing the environment. The business idea for zip-line canopy tours developed from these. Darren Hreniuk, a Canadian citizen who moved to Costa Rica in 1992, around the same time that a scene in the film Medicine Man incorporated the treetop rides, with the goal of using canopy tours to help raise awareness for reforestation, education and socio-economic development in the surrounding areas. In October 1998, the Costa Rican Patent Office granted patent No. 2532 for an "Elevated Forest Transport System Propelled by Gravity, Using Harness and Pulley Through a Simple Horizontal Line" to Hreniuk. The patent was later annulled, bringing uncertainty to zip-line businesses, before being reinstated after twenty years.
A canopy tour (sometimes called a zip-line tour) provides a route through a wooded, and often mountainous, landscape, making primary use of zip-lines and aerial bridges between platforms built in trees. Tourists are harnessed to a cable for safety, and many are restricted to adults. Heights vary from near to the ground to near the treetops. Canopy tours are largely marketed under the banner of ecotourism, although the environmental impact of any type of zip-line is a disputed topic.
The terminology varies (canopy tour, zip-lining, flying fox), and the distinction between using zip-lines for ecotourism and zip-lining as an adventure sport is often not clear. Zip-line tours are now popular vacation activities, found both at upscale resorts and at outdoor adventure camps, where they may be an element on a larger challenge such as a hike or ropes course.
A type of pulley with a grooved wheel known as a sheave is used in zip-lines, and the pulley turns as it travels along, thus reducing friction and enabling greater speed than would otherwise be possible.
The zip-line trolley ("zipliner") is the frame or assembly together with the pulley inside that run along the cable. Zip-lines also have some kind of device to allow the cargo or rider to attach to the pulley system. This could include a harness, seat, a cabin or often just a handhold in smaller playground applications, that attaches to the pulley by a pivoting link or carabiner which secures the load, allowing the person or cargo to travel down the line.
To be propelled by gravity, the cable needs to be on a fairly steep slope. Even then, the rider or cargo will often not travel completely to the end (although this will depend on the load), and some means of safely stopping the car at the bottom end is usually needed with the larger zip-lines. Users of zip lines must have some means of stopping themselves. Typical mechanisms include:
There are certain precautions that can be taken. Riders are physically attached to the cable by a harness, which attaches to a removable trolley. A helmet is required on almost all courses of any size. All zip-line cables have some degree of sag, so the proper tensioning of a cable is important and allows tuning the ride of a zip-line. With the 2023 ACCT standards set to be released soon, the new zipline braking requirements eliminate hand-braking as a braking option as a safety factor. Currently, the standards require a 3:1 factor of safety (safety factor) minimum, but currently, the standards (ACCT/ANSI 2019 and ASTM F2959) require a primary and secondary brake or a fail-safe braking system. A Fail-safe-safe braking system meets the current standards. The 3:1 Safety Factor requirement is not new; the Park City Mountain Resort (PCMR) zipline had a Fail-Safe trolley and compression spring system in 2002. PCMR has had zero-braking-related accidents in 21 years.
The zipline industry is injury-prone compared to several other amusement rides. Cameron Annas (Granite Insurance, NC) recently predicted that the 2022 zipline accidents will double the 2016 accident numbers, see 2023 Adventure Park Insider magazine. In 2020, Cameron Annas (Granite Insurance, NC) published in a virtual ACCT presentation zipline that accident rates for 2016 were 6-7 per 100,000 zipliners, and over half were braking-related. This year, Mr. Annas published a 2022 prediction (15 accidents per 100,000) in the Adventure Park Insider Summer 2023 magazine. I know over half are still braking-related because my zipline accident investigations support the findings.
Industry groups estimate there are more than 400 commercial zip lines in the U.S. across 48 states (the exceptions being Michigan and North Dakota) that service more than 70 million rides annually. The 2022 prediction means that over 10,000 zipline accidents occurred last year. (E-brakes should be required for all ziplines--in order to pass inspection--if we want accidents and insurance policies reduced.) The problem with today's zipline trolleys (two wheels) is momentum (p=mv). Petzl said its tandem-speed pulley could be calculated at 95% gravity (9.3 m/s2).
As engineers know, everyone reaches the lowest point of a zipline at nearly the same time (gravity is constant), but once zipliners go uphill, problems arise. Now, stopping their mass (m) becomes the variable that can triple a zipliner's momentum (p) (e.g., 75-lbs v. 250-lbs riders). Most braking accidents involve heavier zipliners.
The standard should require zipliner arrival speed testing using the maximum and minimum weight requirements for the zipline course. Also, Safety Managers and Third-party Inspectors should be testing and documenting zipline arrival speeds. They should get speeds when temperatures are the lowest of the season and monitor temps, which also change arrival speed due to thermal expansion or contraction of steel zipline cables. For running or cycling, a simple $150 GPS Watch (Garmin) can provide daily speed data.
Arrival speeds for min and max-weight zipliners are not the same on any zipline using two-wheeled trolleys. Some companies have reported a 5-MPH variation. The ACCT 2019 standards say anything over 5-MPH requires a stand-alone emergency brake or EAD (Emergency Arrest Device). Stand-alone E-brakes are not brakes that someone resets. A spring braking system is an example of a stand-alone EAD, and 3:1 safety factors still apply.
What can the ACCT and ASTM F24 do to cut zipline accidents in half? (The answer is simple: Require E-brakes on every zipline, YES, (because accidents can be reduced by 50%).
The world's longest zip-line as of 31 January 2018 is the 'Jebel Jais Flight' from one of the peaks of the Jebel Jais mountain in Ras Al Khaimah, United Arab Emirates, with a single unbroken span of 2,831.88 metres (9,290.9 ft). The ride was temporarily closed pending the outcome into an investigation into the crash of an Agusta 139 rescue helicopter on 29 December 2018, killing all on board. It is believed to have clipped one of the cables. The ride has since re-opened.
The "Parque de Aventura Barrancas del Cobre" at 2,545 m (8,350 ft) in Copper Canyon, Mexico, is the second-longest span, with "El Monstruo" at Orocovis in Puerto Rico coming in third, at 2,530 m (8,300 ft).
The Skywire at Bluewater in Kent is the longest in England at 725 metres (2,379 ft). The longest zip-line in Europe, at just over 1,600 metres (5,200 ft), is the Zip World Bethesda line in Penrhyn Quarry, Bethesda, Wales. The Zip World Bethesda line also holds the world record for attaining the fastest zip-line travel speed.
Zip-lines with the steepest inclines include:
The La Tyrolienne in Val Thorens, France is the highest altitude zipline, at 10,600 feet.
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