Isolation tank

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This article is about the sensory deprivation device. For other uses, see Tank (disambiguation).
A modern isolation tank

An isolation tank, originally called a sensory deprivation tank (aka float tank, flotation tank or sensory attenuation tank) is a lightless, soundproof tank with high epsom salt (magnesium sulphate) content in which the participants float in salt water at skin temperature. They were first used by John C. Lilly[1] in 1954 to test the effects of sensory deprivation. In 1970’s, the effects of sensory deprivation was further investigated more rigorously by the team of Peter Suedfeld and Roderick Borrie from University of British Columbia, who renamed sensory deprivation to "Restricted Environmental Stimulation Therapy" (REST). However, in the literature it is often referred to as ‘flotation REST’ and has been academically studied in the United States and in Sweden with published results showing reduction of both pain and stress.[2] As a result, float tanks were produced for commercial uses and the number of flotation centers has grown in dozens of countries in the last decade. The San Francisco Bay Area has seen a recent growth in such centers.[3]

Floation is widely advertised on the internet as a form of alternative medicine with claims that it has benficial health effects, but these claims are not backed by good evidence.[4]


The isolation tank was developed in 1954 by John C. Lilly, a medical practitioner and neuropsychiatrist.[5][6][7] During his training in psychoanalysis at the US National Institute of Mental Health (NIMH), Lilly experimented with sensory deprivation. After 10 years of experimentation without taking any psychoactive substances, he tried floating in combination with a psychedelic agent, mostly LSD (at that time he was a researcher at NIMH, and LSD was legal in the US). He found that floating alone, without taking any substances, was a much better experience because of non-disturbed consciousness.[8]

In neurophysiology, there had been an open question about what keeps the brain going and the origin of its energy sources. One hypothesis was that the energy sources are biological and internal and do not depend upon the outside environment. It was argued that if all stimuli are cut off to the brain then the brain would go to sleep. Lilly decided to test this hypothesis and, with this in mind, created an environment which isolated an individual from external stimulation. Peter Suedfeld and Roderick Borrie of the University of British Columbia began experimenting on the therapeutic benefits of isolation tanks in the late 1970s. They named their technique "Restricted Environmental Stimulation Therapy" (REST).

Tank design and usage[edit]

Initial isolation tanks were uncomfortable. Users were entirely submerged in the tank, which required them to wear a breathing apparatus and tight clothing. Users complained that the discomfort from the mask and clothing distracted from the isolation experience and that complete submersion led to fear of drowning.[9] In current tanks, users are not submerged; instead, they float. This is done with a solution of epsom salt that increases water density, allowing the human body to float. Users float face-up in a relaxed position, with the face above the water and the ears submerged. This reduces the user's hearing, particularly when using ear-plugs as protection against the salt water. Users are encouraged to let their arms float to the side to further reduce skin sensation. This occurs because the air and water are the same temperature as the skin, and the feeling of a body boundary fades. The user's sense of smell is also greatly reduced, especially if the water has not been treated with chlorine. The density of the water prevents rolling over, even if asleep.

Another difference between early designs and current tanks is that tanks now face increased regulation of disinfection. In America, different states have implemented different rules. In Europe, the DIN 19643 bathing water standard requires automated chlorination controlled by REDOX (ORP) measurement. Chlorine, bromine and peroxide disinfection have all been used successfully. Most isolation tanks use a surface skimmer, cartridge filtration as a means of disinfection, and ultraviolet sterilization and chemicals to keep the water free of microbes and sediment. These machines are usually turned off during a session to keep the isolation space as quiet as possible. A ring heating system can be used around the outer walls of the tank so that warm water rises around the edges of the pool, travels towards the center, and then sinks under the tank user. This very slow water convection flow helps to keep the user centered in the middle of the pool. The small waves caused by breathing also aid in centering the subject.

Isolation tank construction and plumbing is typically all plastic. In most cases, glass reinforced resins are used. High quality flotation tanks may use acrylic or medical stainless steel which is impervious to the high salt concentration and more importantly the disinfectants. Epsom salt is not corrosive in the way sodium chloride is, but unsealed stone and concrete surfaces outside the tank can be damaged by splashed or dripped salt water as the recrystallizing salt opens up cracks and fissures as it dries. Chlorine used as a disinfectant can attack some surfaces such as marble.

Having plumbing facilities immediately next to the tank is also helpful when the water must eventually be changed to prevent microbe growth. The plumbing, including the drain pipes, should be constructed of plastic to prevent deterioration from the salt. The salt concentration may need to be diluted when discarded, to prevent damage to small private wastewater plumbing systems.

Generally, users of isolation tanks enter the pool nude. Swimsuits are discouraged, as the elastic material can create uncomfortable compressed stress points on the skin during the session. Due to the high salt content, the water is rarely changed, and all users are expected to shower, wash with soap, and rinse clean prior to entering the tank to avoid getting oils from their skin into the tank. The user rinses again after a session to remove excess epsom salt from the skin. White vinegar can be used to remove excess salt from the ear canal and hair.

Alternative medicine[edit]

Flotation has been widely advertised on the internet as a form of alternative medicine that has a number of health benefits, but the claims are often exaggerated and poorly-evidenced.[4] Despite the lack of scientific support, people have sought treatment from flotation for many conditions including muscle tension, chronic pain, hypertension, and rheumatoid arthritis to PMS.[10]

Notable users[edit]

The physicist Richard Feynman's experiences in a sensory deprivation tank were documented in the popular book Surely You're Joking, Mr. Feynman!. Feynman was invited to try the isolation tank at John Lilly's home after Lilly attended one of Feynman's popular lectures on quantum mechanics.[citation needed]

American Chef Anthony Bourdain was a regular user of flotation tanks in the 1980's after long shifts running a restaurant.[11]

Carl Lewis used in-tank visualization techniques to prepare himself for his gold medal long jump at the 1988 Seoul Olympics.[12]

John Lennon reportedly used a flotation tank in 1979 in an attempt to kick his heroin habit.[13]

See also[edit]


  1. ^ Lilly, John C. & E.J. Gold (2000). Tanks for the Memories: Flotation Tank Talks. Gateways Books & Tapes. ISBN 0-89556-071-2
  2. ^ Kjellgren A, Sundequist U, et al. "Effects of flotation-REST on muscle tension pain". Pain Research and Management 6 (4): 181-9
  3. ^ Efrati, Amir. "Float Centers Gaining Steam". The Wall Street Journal. Retrieved May 15, 2013. 
  4. ^ a b Jonsson K, Kjellgren A (2014). "Curing the sick and creating supermen – How relaxation in flotation tanks is advertised on the Internet". European Journal of Integrative Medicine. 6 (5): 601–609. doi:10.1016/j.eujim.2014.05.005. ISSN 1876-3820. 
  5. ^ Black, David (December 10, 1979). "Lie down in darkness". New York Magazine. 12 (48): 60. ISSN 0028-7369. 
  6. ^ Gelb, Michael; Sarah Miller Caldicott (2007). Innovate Like Edison. Dutton. p. 140. ISBN 0-525-95031-1. 
  7. ^ Lilly, John Cunningham (1996). The Scientist: A Metaphysical Autobiography (3 ed.). Ronin Publishing. p. 102. ISBN 0-914171-72-0. 
  8. ^ Lilly, John C. (2002). The Deep Self: Consciousness Exploration in the Isolation Tank. pp. 59–60. ISBN 978-0895561169. 
  9. ^ Seudfeld, Peter. "History of Floating". Portland Float Conference. Float Conference. Retrieved 9 March 2013. 
  10. ^ "Why do people use flotation tanks?". BBC News Magazine. 2016-02-09. Retrieved 2016-09-23. 
  11. ^ "Bourdain in the Tank | FIGHTLAND". Retrieved 2016-09-23. 
  12. ^ "Floatation Tanks, Three Powerful Healing Therapies in One!". CNN iReport. Retrieved 2016-09-23. 
  13. ^ Times, Special To The New York (1981-11-21). "RELAXATION TANKS: A MARKET DEVELOPS". The New York Times. ISSN 0362-4331. Retrieved 2016-09-23.