Investigation of a cluster of decompression sickness cases following a high-altitude chamber flight

Although relatively safe, hypoxia exposure is a mandatory training requirement for aircrew that carries the risk of decompression sickness (DCS). Usually DCS affects only one individual at a time. Here, a cluster of three simultaneous cases is reported. Since these numbers were well in excess of the usually encountered incidence rate, the purpose of this work was to identify the most likely reasons using the epidemic DCS investigation framework which involves four main considerations: time; place; population; and environment. Based on time and place observations, this cluster clearly falls into the individual-based classification, where the environment is a primary concern. Indeed, equipment analysis allowed us to identify the most likely reason for two out of three cases (perforations in the oro-nasal oxygen masks worn during training). It led to replacement of damaged equipment and modification of teaching to prevent such damage. It is recommended that this investigative template may be used for any future occurrences of DCS in clusters.