A crane lowers a t-piece into place on top of the Oro Hondo Shaft.

Crane lowers a "t-piece" component onto the Oro Hondo exhaust shaft at the Sanford Underground Research Facility in Kirk Canyon near Lead, South Dakota. 

Photo courtesy Andrew Brosnahan

Clearing the air: SURF ventilation upgrade supports underground activities

SURF’s improved ventilation achieves 100% redundancy, supports large-scale excavation work

A successful upgrade to the Sanford Underground Research Facility's (SURF) Oro Hondo fan complex will ensure uninterrupted air supply to support world-leading research at SURF, including the massive cavern excavation for Fermilab's Deep Underground Neutrino Experiment (DUNE). 

“As America’s underground science facility continues to grow, our investment in infrastructure improvements ensures that our science partners have consistent and reliable access to this world-class facility,” said Mike Headley, executive director of the South Dakota Science and Technology Authority, which manages SURF.

Underground airflow at SURF is critical. Air flows down the Ross and the Yates shafts (the two main access shafts) and across hundreds of miles of drifts, ramps, and shafts. Fresh air keeps the temperature from rising; vents exhaust from diesel-powered excavation equipment; creates a quieter background for science; and, most importantly, provides breathable air. 

The driving force of this airflow is a massive fan at the top of the Oro Hondo Shaft, the main exhaust pathway. This 2,000-horsepower Oro Hondo fan is 15,000 times more powerful than an average home ceiling fan on full blast. Generating up to 500,000 cubic feet of airflow every minute, the Oro Hondo fan provides sufficient airflow for all underground activities.


In this Google Maps satellite image of the Lead area, the locations of the Ross Campus, Yates Campus, and Oro Hondo fan complex are identified. 


Prior to SURF’s ventilation upgrade, when the main fan was turned off for maintenance or upgrades, underground operations had to rely on a smaller, secondary fan. “SURF outgrew our previous backup fan’s capabilities, which could only produce about 151,000 cubic feet of air per minute,” said Andrew Brosnahan, SURF facility engineer and project manager for the Oro Hondo fan upgrade. “This wasn’t enough to support larger projects, like the DUNE excavation.”

In early 2022, construction began on a major upgrade to the Oro Hondo fan complex, which included the installation of a large secondary fan to replace the smaller backup unit. SURF’s team of engineers worked with Howden, a global manufacturer, to custom design enormous components that would allow exhaust from the Oro Hondo Shaft to be directed toward either fan.

“It’s as if we placed a mirror against our existing infrastructure, adding a redundant fan system,” Brosnahan said. “Now, each individual fan generates enough airflow to support all operations, excavation, and science activities underground.”

The project also included major electrical upgrades. Overhead electrical lines between the Oro Hondo substation and the fan complex were replaced with an underground duct bank. Crews also modernized several switchgears and transformers and replaced an old electrical building with a modernized, prefabricated electrical house. 


Overhead electrical wires (left) were replaced with an underground duct bank (right). Photo courtesy Andrew Brosnahan. 

SURF partnered with several local contractors to complete digging and demolition work, prepare foundations for the new fan and electrical house, test and commission equipment, install the fan, and provide overhead cranes for major lifts.

“The completion of this project gives SURF 100% redundancy and allows our facility to support large-scale excavation work without interruption,” Brosnahan said.

In April, crews completed the installation of the new fan and commissioning is expected to complete in June 2023. 

Members of the SURF team explored SURF's underground ventilation at "Deep Talks: Going with the (air)flow" on April 20, 2023. Watch the full presentation below.