Could nitrogen leaks during a Texas execution be dangerous?

The BBC is carrying a story that a Texan murderer is to be asphyxiated breathing pure nitrogen from a mask:

https://www.bbc.co.uk/news/world-us-canada-68053917

(Leaving the moral questions aside) Dr Joel Zivot, an associate professor in anaesthesiology at Emory University's School of Medicine is quoted in the article as saying there is a danger to anyone else in the room from nitrogen leaks:

"He warns of unintended risks from the presence of pure nitrogen changing the oxygen-to-nitrogen ratio in the execution chamber, especially as Smith could hold his breath or move his head against the mask, or the equipment could leak. "Some of it will be exhaled [by Smith] along with carbon dioxide and some of it may leak out of the mask. And I think that that presents a real and material danger to this execution," Dr Zivot said."

This article says that you don't pass out until oxygen drops to 10% or less (presumably at sea level pressure):

https://www.skuld.com/contentassets/4867cb8cc9f842a08c25d29050654527/oxygen-levels---skuld.pdf

From the picture in the article I would guess that the execution room is at least 50m^3 in volume.

To dilute the air in the room from ~20% to ~10% oxygen throughout the room would require ~50m^3 of nitrogen to leak from the mask or equipment (more if the room is not airtight). Apparently a 5' nitrogen tank only hold ~6.5 cubic meters of nitrogen!

Allowing for the fact there is likely to be a concentration gradient, you would need to reduce the whole room to 10% oxygen. But it still seems barely credible that many cubic meters of gas are going to leak, unless the executioners are totally incompetent. Am I missing something or does the prof need to re-do his calculations?