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No Longer Under Pressure: NIST Dismantles Giant Mercury Manometer

Video by: Jennifer Lauren Lee/NIST. Animations: Sean Kelley/NIST. Music: Blue Dot Sessions. Photos: Bruce Johnson and Jay Hendricks/NIST


For the last 30 years, the official U.S. standard for measuring pressure has been a 3-meter-tall (about 10-foot) device called a manometer. American industry relies on the U.S. pressure standard for everything from silicon chip manufacturing to sensors that tell pilots how high their planes are flying. 

Last month, NIST workers decommissioned the U.S. standard manometer’s nearly identical twin, kept on hand as a backup for the main device. The twin device was dismantled as part of a global effort to phase out instruments that rely on mercury, a toxin. 

"This is an exciting first step in decommissioning our mercury manometer program at NIST to make way for our new standard,” said NIST physicist Jay Hendricks. The new standard – called the Fixed Length Optical Cavity (FLOC) – will be a smaller, portable machine that makes its measurements using light. 

The manometer’s twin holds approximately 225 kilograms (500 pounds) of mercury when full, but for years it has been nearly empty. Dismantling the giant column of mercury and glass took about half a day and required draining the residual mercury still trapped inside the instrument. The device was so tall that workers had to lift the machine’s casing – a 3-meter-long cylinder of metal – through a pre-cut hole in the laboratory ceiling. The sensitive equipment was then carefully dismantled and sent off-site for special disposal. The residual mercury was also sent off-site, to a plant that specializes in recycling the toxic substance.

Were there any surprises? Not really, Hendricks said, because they had been preparing for the decommissioning event for several weeks.

"When you're dealing with a complicated disassembly like this, you try and think ahead a couple of steps, because there's so many things that could go wrong,” Hendricks said. “But because we knew the construction of the device, and we had studied the blueprints, we knew where the tricky points would be. And everything really went without a hitch."

Though the disassembled manometer may be no more, its identical twin continues to serve as the official U.S. pressure standard. But Hendricks said that device will eventually be disassembled as well, as it will soon be replaced by the new optical-based FLOC standard.

-- Reported and written by Jennifer Lauren Lee

Released June 28, 2019