This paper reports on the experimental work performed in support of the development of a technical standard for helicopter emergency breathing systems (EBS), and also contains the resulting technical standard. The work was commissioned by the UK Civil Aviation Authority (CAA) and was funded by the CAA, the UK Health and Safety Executive and Shell Aircraft International. The project formed part of the jointindustry Helicopter Safety Research Management Committee (HSRMC) programme of work and was performed by Dr Susan Coleshaw, an acknowledged expert in the field of offshore safety and survival.