Police investigating the accident said that the hydrofluoric acid spill may have been caused by human error as two workers were unloading the chemical from a delivery tanker. A closed circuit security video camera recorded the two workers on top of the tanker, both without protective gear. They were connecting an air hose to a valve in the tanker in order to force the chemical out under high pressure. The video shows white vapour erupting at high pressure from the tanker, engulfing the workers.