Hypothetical scenario: There is a dome on the moon containing an Olympic-size swimming pool. Our intrepid hero is receiving a scuba diving lesson at the bottom of the pool (3m) when a hull breach occurs and the pool is exposed to vacuum. How long does he have to live?
This question is similar to Boiling ponds and pools on Mars?. The biggest difference is that the gravity is much lower, which greatly reduces the available pressure to breathe with and might plausibly cause asphyxiation.