Ventilation or aerosol extraction: comparing the efficacy of directional air purifiers, HEPA evacuators and negative-pressure environments

Background

This study evaluated aerosol exposure during various respiratory activities (breathing, tachypnea, coughing, and oxygen therapy) in environments with directional air purifiers (DAPs), HEPA evacuators, and standard negative pressure (SNP) rooms to explore potential alternatives for addressing isolation room shortages.

Methods

Aerosol exposure was measured during various breathing conditions (normal, tachypnea, coughing, and recovery) with non-rebreather masks (NRMs) and nasal cannulas. The study analysed aerosol velocity and concentrations at the head, trunk and feet of a mannequin across settings including DAP, HEPA evacuator, SNP room, their combinations, and a reference group without intervention.

Findings

The DAP, HEPA evacuator and SNP environment all reduced aerosol build-up compared with the control group. The DAP and HEPA evacuator were consistently more effective than the SNP environment, especially during activities that increase expiratory flow. The HEPA evacuator showed higher aerosol concentrations at the head compared with the DAP when used with NRMs or nasal cannulas. Both the DAP and HEPA demonstrated better aerosol clearance than the SNP environment when minute ventilation exceeded 10 L/min.

Conclusions

DAP and HEPA evacuators provide effective aerosol reduction, suggesting their utility as alternatives to SNP isolation rooms during pandemics. While SNP environments continuously ventilate the space, DAP and HEPA evacuators are more efficient in early aerosol removal, preventing accumulation. However, aerosols dispersing in multiple directions during oxygen therapy can challenge the HEPA evacuator's single-point suction, unlike the broader coverage offered by the DAP.