Officials from NASA and Russia’s space agency don’t see eye to eye on the causes and risks of small but persistent air leaks on the International Space Station.

That was the word from the new chair of NASA’s International Space Station Advisory Committee last week. The air leaks are located in the transfer tunnel of the space station’s Russian Zvezda service module, one of the oldest elements of the complex.

US and Russian officials “don’t have a common understanding of what the likely root cause is, or the severity of the consequences of these leaks,” said Bob Cabana, a retired NASA astronaut who took the helm of the advisory committee earlier this year. Cabana replaced former Apollo astronaut Tom Stafford, who chaired the committee before he died in March.

The transfer tunnel, known by the Russian acronym PrK, connects the Zvezda module with a docking port where Soyuz crew and Progress resupply spacecraft attach to the station.

Air has been leaking from the transfer tunnel since September 2019. On several occasions, Russian cosmonauts have repaired the cracks and temporarily reduced the leak rate. In February, the leak rate jumped up again to 2.4 pounds per day, then increased to 3.7 pounds per day in April.

Russians believe the cracks are caused by “high cyclic fatigue caused by micro-vibrations,” Cabana said earlier this month, and NASA thinks the issue is “multi-causal,” caused by “pressure and mechanical stress, residual stress, material properties, and environmental exposures.”

They also can’t seem to agree on how catastrophic the leaks might be.

While the Russian team continues to search for and seal the leaks, it does not believe catastrophic disintegration of the PrK is realistic,” Cabana said, according to Space News. Meanwhile, he said that NASA has “expressed concerns about the structural integrity of the PrK and the possibility of a catastrophic failure.”

The two parties are locked in a stalemate. Russians think it is safe to continue operations of the PrK module, but can’t prove it. And Americans think it is unsafe to continue, but can’t prove that either.

“This is an engineering problem, and good engineers should be able to agree on it,” Cabana added.