Float on

Steve Brown has been talking about his tank for months now. He has told his in-laws and his neighbors along with a few friends and a careful selection of co-workers.

"I will mention it, and depending on the reaction I get from people, I will explain," said Brown, 45. "I can sense who is squeamish about it and who is a little more open to it."

Brown is talking about his flotation tank, also known as a sensory deprivation tank or isolation tank. He built it in the garage of his East Bridgewater home. "If I want to float at midnight, I can float at midnight," he said.

Brown is one of a small but growing number of people who say they benefit from spending time in an enclosed tank.

"Something about it is just captivating," said Brown, a WBUR-FM radio host who started floating in 2001. "The fact that you can just unplug from everything and can be able to just shut everything off and be in total silence and total darkness."

Isolation tanks entered the public consciousness in 1980 with the movie "Altered States," which stars William Hurt as Dr. Eddie Jessup, who turns into a goat-eating creature after taking acid in a sensory deprivation tank. The movie, combined with fears of claustrophobia and drowning, did not bode well for the budding flotation tank industry.

Scientist John Lilly invented the isolation tank in 1954 while working for the National Institute of Mental Health. Lilly -- known for his interspecies communication research and credited with promoting the enactment of the Marine Mammal Protection Act in 1972 -- invented the isolation tank to study the human mind in the absence of external stimuli, such as light and sound. He and other researchers studied small groups of people with chronic pain, stress, anxiety, and other ailments who found relief after repeated sessions in a tank. Some floaters said that time in the tank seemed to enhance creativity and athletic performance. Some even reported life-changing spiritual experiences.

The first tank was like a giant, upright tube filled with water. Floaters would climb in wearing nothing but an opaque mask and breathing apparatus. The design evolved into a standard horizontal model much like the one Brown has in his garage. He said he bought the plans for it off the Internet for $25 and spent another $2,500 building it.

Brown's tank is an insulated plywood box that resembles an abnormally large coffin or closet turned on its side. (Commercial models are usually made of fiberglass.) On one end is a small, lightweight square door through which the floater enters. The inside is covered with a custom-made black vinyl liner and filled with 200 gallons of water mixed with 800 pounds of magnesium sulphate, or Epsom salt. The salt enables users to float on top of the water. (The average concentration of the mineral in tanks is around 53 percent. In the Dead Sea, it is about 33 percent.) A heater on Brown's tank keeps the water temperature at 94 degrees, or skin temperature. This eliminates the sensation of touch. A pump circulates the water through an ultraviolet filter between float sessions to keep it clean.

In recent years, more sophisticated tank designs have emerged. Some feature underwater sound systems and flat-screen televisions, and can be custom designed in different colors and shapes that resemble ovular pods more than boxes. Such models can cost more than $10,000.

Brown said he climbs in his tank every other day for about an hour, wearing nothing but silicone earplugs. When he first gets in, Brown said he makes different kinds of sounds to clear his mind until he falls into a deep state of relaxation.

"You have no concept of time," he said. "You hear your breath. You hear your heart. All of a sudden you realize the stuff you are hearing is from yourself."

Those who are not ready to build their own tank can float at spas that offer sessions to the public, such as Driftaway Floatation Spas in Burlington. Driftaway has three "float spas" instead of tanks, which were modeled after designs used in London. The spas are small rooms with a pool of salt water at the bottom. They are equipped with an internal light and underwater speakers, which clients can turn on or off.

"It should be a luxury experience," said Driftaway owner Jeff Laughlin, who also manufactures the float spas. He said he just sold two to a spa in South Carolina. Floaters can bring in their own music or audio programs. "I have a lawyer who comes in and listens to Portuguese," said Laughlin, 45.

Laughlin charges $75 for a single, hourlong float and offers packages ranging from $300 to $1,250, along with monthly memberships that cost between $45 and $125. He said about 500 people have visited Driftaway since it opened in October.

"The challenge is to bring it to the mainstream," he said. "If someone is into meditation, yoga, nutrition, exercise, and wellness, they are going to like this kind of therapy."

On a recent Thursday evening at the spa, four regular floaters lounged in brown leather recliners and sipped herbal tea.

"I am cooked," said James Policastro, 60, of Boston. He had just finished his weekly float session, which he said, for him, is sometimes like a "rebirthing experience."

"It moves you into an altered state," he said. "The feeling is truly remarkable."

Margaret Ryan and her husband, Lawrence Paolella, were preparing for their float. They come to Driftaway twice a month from their home in Somerville.

"Imagine that you are back in the womb," said Ryan, 58. "It is very warm, like being in a great big bathtub where you just kind of play."

Ryan and Paolella, 69, learned about flotation from their friend Cheryl Chong-Hunter, who is a yoga instructor. Chong-Hunter, 42, said she also learned about flotation from a friend, which is pretty much how people have learned about it all along -- via word-of-mouth.

"When you discover something that good, you just want to share it with your friends," Chong-Hunter said. "It is experiential. You have to just try it."