In April 2015, an underground surveyor arrived at the level that accessed the top of a recently completed stope to conduct a cavity monitoring survey (CMS). After removing the danger and warning signs at the level access, the surveyor reversed the light vehicle towards the open stope expecting to encounter a second set of signs hanging in the access, in accordance with the site's standard procedure. This was the location commonly used to unload the survey equipment.
The vehicle reversed until the rear wheels dropped over the edge of the 18 metre deep open stope, and the frame bottomed out on the floor at the edge of the void. The vehicle’s frame skidded 20 to 30 centimetres before stopping. The expected second set of signs had not been hanging in the access.
Using the vehicle’s two-way radio, the surveyor called for emergency assistance. An underground loader arrived shortly after and the vehicle was secured to the loader using a chain. On arrival, the emergency response team further secured the vehicle with additional slings and rope then extracted the surveyor through the driver’s side window. Fortunately, the individual was not injured.
Direct causes
- The open stope lacked appropriate hard barriers, allowing personnel inadvertent access to the void.
Contributory causes
- Management relied on the lower order control of signage with no hard barriers to prevent access to the top of the open stope.
- The signage process in the site's signage procedure was inconsistent (i.e. reliance on a second sign being in place that was not).
- There was no official procedure for conducting a cavity monitoring survey.
- There was insufficient detail in the procedure for working around an open hole (which is different from working at heights).