To what extent HFNC increases indoor oxygen concentration and facilitates the risk of fire?

Introduction: HFNC delivers an air/oxygen mixture at a flow of up to 80L/min and oxygen concentrations up to 100%. During the Covid-19 pandemic HFNC was accepted as first-line respiratory support used commonly in temporary hospitals. Now HFNC is used in standard hospital rooms with often smaller cubature. Oxygen room concentration of more than 23.5% is deemed dangerous regarding the risk of fire. Methods: To assess the change of oxygen concentration in the room atmosphere a HFNC device was placed in a double-bed hospital room (57.5m3) with a standard European ventilation system. The HFNC was set on a flow rate of 60L/min, FiO2 0.9, and 37°C, medium sized cannula was placed on the bed. Hourly room air exchange was 100m3/h (Flowmeter Testo 435, Poland). The experiment was conducted, with an open door (Ex.1) and with a closed door (Ex.2). Certified oxygen detectors with dedicated software (DG-P9E/M with measuring range 0-25 %Vol. O2, Gazex, Poland) recorded oxygen concentration at 5 seconds intervals. Results: During Ex.1, the threshold of 23.5% was exceed in 20th and 37th minute was periodical and maximum value reached 23.8%. Mean oxygen concentration stopped rising at 46th minute and remained stable at an average level of 22.6%. In Ex.2, the oxygen concentration of 23.5% was detected in 48th minute and increased further. The study was then terminated at 53rd minute due to safety concerns. Conclusion: Our findings show that the number of HFNC devices in a hospital room should be limited, additional room ventilation should be provided, (e.g., opened door) and oxygen concentration should be measured, because HFNC may result in an excessive oxygen concentration, increasing the risk of fire.