Researchers have tested the efficacy of N95 filtering face piece respirators in conditions of constant and cyclical air flow, simulating human breathing, from 42 to 360 L/min. N95 respirators are the personal safety equipment most commonly used by industrial and health-care workers to protect themselves against exposure to ultrafine particles (UFPs).

The results showed that an increase in both peak inhalation flows (PIF) and breathing frequency could potentially raise the particle penetration through N95 FFRs. However, the effect of PIF was observed to be much more important than the effect of the frequency. It was also shown that, among three constant flows equal to the cyclic flow PIF, mean inhalation flow (MIF) and minute volume, a constant flow equal to MIF can much better predict the initial penetration of N95 FFRs obtained under the cyclic flow.