The trench effect and eruptive wildfires: lessons from the King’s Cross Underground disaster

Fire eruption (also known as ‘blow-up’ or ‘flare-up’) is a very dangerous aspect of wildland fire behaviour. It poses a significant threat to the safety of wildland fire-fighters and complicates the broader problem of wildfire risk management in complex terrain. Despite the seriousness of eruptive fire events, operational wildland fire spread models generally do not account for the possibility of these events occurring and there is little in the literature devoted to obtaining a model that consistently describes the phenomenon. To address this situation international researchers have recently proposed models that account for eruptive fire behaviour as a feedback process, with possible mediation by other factors. One such factor is flame attachment to steep slopes. The concept of flame attachment is also of interest in the structural fire-fighting context. For example, it is a key component of the so-called ‘trench effect’ which is a well established mechanism for fire propagation on enclosed slopes such as escalators or stairwells in building structures. Studies into structural fires have revealed that the trench effect can produce extreme fire behaviour and rapid fire spread, as was apparent in the 1987 Kings Cross (London) Underground fire disaster, for example. Despite the well known implications of the trench effect in the structural fire context it has received little attention in the wildfire context. We therefore consider the trench effect in a wildfire context as a possible trigger for eruptive fire behaviour. In particular we consider the findings of a number of inquiries into fatal and near-fatal incidents apparently involving eruptive fire behaviour and discuss the possible involvement of a landscape-scale trench effect in these incidents.