Oxygen is the most commonly administered therapy in critical illness. Accumulating evidence suggests that patients often achieve supra-physiological levels of oxygenation in the critical care environment. Furthermore, hyperoxia related complications following cardiac arrest, myocardial infarction and stroke have also been reported. The underlying mechanisms of hyperoxia mediated injury remain poorly understood and there are currently no human in vivo studies exploring the relationship between hyperoxia and direct pulmonary injury and inflammation as well as distant organ injury. The current trial is a mechanistic study designed to evaluate the effects of prolonged administration of high-flow oxygen (hyperoxia) on pulmonary and systemic inflammation. The study is a randomised, double-blind, placebo-controlled trial of high-flow nasal oxygen therapy versus matching placebo (synthetic medical air). We will also incorporate a model of acute lung injury induced by inhaled endotoxin (LPS) in healthy human volunteers. Healthy volunteers will undergo bronchoalveolar lavage (BAL) at 6 hours post-intervention to enable measurement of pulmonary and systemic markers of inflammation, oxidative stress and cellular injury.