Which criteria applies to the use of a scavenger system in NO procedures?

The criteria that requires a scavenger system in nitrous oxide (NO) procedures focuses on the necessity to prevent overexposure to nitrous oxide. This is crucial because nitrous oxide can lead to potential health risks for both patients and dental professionals if inhaled in excessive amounts. Scavenger systems effectively capture and eliminate excess gas during procedures, ensuring that the concentration in the environment remains within safe limits. By adhering to this guideline, practitioners can enhance safety standards in their practice, maintaining the well-being of all involved during procedures that utilize nitrous oxide.

The other options either suggest conditions under which a scavenger system would not be necessary or misapply the context in which these systems should be utilized, neither of which aligns with the fundamental safety requirements set forth for the use of nitrous oxide.