compared with the general ward, suggesting that sicker patients, or the therapies they require, increase viral dispersion. Several barrier enclosures have recently been described for use during tracheal intubation and extubation of COVID-19 patients [4, 5] . Whereas these enclosures contain visible fluorescent particles during simulated coughing, they increase the difficulty of the procedure by restricting movement, and there is insufficient evidence that such enclosures actually protect staff from viral spread. We set out to test whether simple physical barriers reduce the spread of small airborne particles and if the addition of negative airflow improves their effectiveness.
Our team constructed a transparent four-sided polycarbonate enclosure similar to the design used by Canelli et al. [4] . The enclosure was modified with two wall proximity to the enclosure. Without any suction, particle detection outside the chamber increased many times above the ambient level after 5 min. However, when attached to one (55 l.min -1 ) or two (100 l.min -1 ) wall suction connections, particle increase was negligible (Fig. 2) .
During visual testing with fog (propylene glycol in deionised water), leakage of fog outside the chamber was also greatly reduced when suction was applied to the enclosure.
In conclusion, a simple enclosure may contain visible droplets, but is insufficient to protect against smaller aerosolised particles during simulated conditions. This was true even when a drape was placed over the opening for the torso and access holes were covered. However, when paired with wall suction and HEPA filtration, such an enclosure 