Most people like Concord’s iconic gasholder because of what’s above ground: the handsome round brick building with a charmingly off-tilt cupola. But for those in the know, the underground part is what matters.
And that’s where engineers will be Wednesday, Dec. 17, in the latest step toward preserving the historic structure.
A crew from Structures North Consulting Engineers and Yankee Steeplejack Company will go beneath the floor to determine the condition of the internal machinery that held and pressurized coal gas for six decades. It’s possible that they will be the first people to enter that space since operations began in 1888, said Althea Barton of the New Hampshire Preservation Alliance.
Many gasholder buildings still exist, including a small one at St. Paul’s School, but Concord’s is one of the very few that still has all the underground mechanism in place. That has long drawn attention from historic preservationists — the Smithsonian Institute expressed concern about saving the building back in 1976 — but it makes preserving the building more complicated.
The work won’t be visible from the outside. Concord Fire Department rescue squad and vehicles will be on standby to comply with federal OSHA regulations for confined spaces, where buildup of invisible gases and possible structure collapse can pose extreme danger.
The research will lead to conclusions about what can or can’t be done to stabilize and preserve the underpinnings of the building. The gasholder’s roof and outer structure have been stabilized over the past year.
The team hopes to conduct restoration work in 2026 as part of ongoing efforts to use the gasholder and the property in some way. The building’s owner, Liberty, which once wanted to tear down the building because of maintenance costs, has gotten the Public Utilities Commission’s permission to use up to $2.4 million in ratepayer funds for its preservation .
How the gasholder worked
Gasholders were built throughout the industrial world in the decades before long-distance gas pipelines existed. They held a flammable gas made from coal that in most cities, including Concord, was sent through local pipelines to light streetlamps and heat or light buildings.
The building sits over a 24-foot-deep basement that was filled with water and held a floating metal tank that lacked a bottom, rather like an upside-down cup. The brick building served as protection from the elements.
The gas was manufactured from coal brought here by rail using a couple of different methods in buildings scattered around the 2.4-acre site, all of which were torn down in the 1990s. The gas was sent to the gasholder building through an underground pipe into the basement, where it bubbled up through the water into the floating tank.
As gas was pumped in, the floating tank would slowly rise from its initial position flush with the floor, guided by vertical rails still visible on the walls. When full, the metal tank was almost 24 feet above the ground and covered all the windows.
As the gas was used in Concord , the tank would sink. As new gas was pumped in, the tank would rise. The amount of gas in the tank could be seen outside on a large scale on the building’s east side, marked by a movable arrow attached to the top of the tank.
This system was used in virtually all gasholders, including a metal tank that stood on this property from 1921 until it was torn down in the 1980s. That metal tank was sealed and didn’t need a building for cover, so passers-by could see the entire metal structure rise and fall as gas levels changed.
Pipelines carrying natural gas, methane, were extended to Concord in 1952 and the much cheaper fuel quickly took all the business from coal gas, which was also known as “manufactured gas.” The gasholder was used for a time to hold natural gas while the new network expanded but has been empty for at least three decades.
Preservation issues
A major complication in preserving the Concord gasholder is that the top of the “cup” that held gas is not thick or sturdy enough to be used safely as a floor. A network of beams have been built over it to support workers and a scaffolding that helped support the roof, but any attempt to use the interior of the building would probably require covering the cup, ruining its historic value.
A big question to be answered involves the condition of the subterranean area, which was designed to be often full of liquid but has been empty for decades.
Saving the building is just part of a neighborhood revitalization many people hope will involve restoring the whole property on South Main Street. Various ideas have circulated for parks, museums and other uses.
For more information, see www.saveourgasholder.org.