I'm pretty sure they're saying they didn't experiment on anyone over 0.15 BAC, because they felt that those people were unable to give true consent.
How this intoxication level was measured? I seriously doubt they carried scales and analyzed blood samples, before asking for consent!
https://www.startribune.com/does-booze-relieve-pain-u-resear...
The same “breath” reading could give you 15% different results depending on the country the test is taken in…
https://www.dart-sensors.com/breath-alcohol-conversions-for-...