Passenger safety during aircraft emergencies attracts considerable attention in the media.1 Fortunately, the dramatic is also the rare, so for most air travellers emergency considerations are academic. Comfort and wellbeing during normal flight are, however, of concern to all, and recently the quality of the environment in aircraft cabins has come under scrutiny. This has followed reports that nausea, headaches, and mucosal irritation are common; that poorly ventilated cabins may spread disease among passengers; and that environmental contaminants such as tobacco smoke may increase the risk of respiratory illness. Thus aircraft manufacturers devote much attention to national regulatory requirements for ventilation, pressurisation, and the composition and filtration of cabin air.2

Until the late 1980s about 0.57 m3 fresh air was delivered to the cabin per person per minute. In modern aircraft this figure has been halved although the total requirement remains the same: consequently, the rest is recirculated air. It was concern about contamination of recirculated cabin air with environmental tobacco smoke, and the increased awareness of the risks of …