Incidents related to borehole logging and portable density moisture gauges

Borehole logging sources and portable density moisture gauges (PDMGs) are used to determine the density and moisture of earth. Borehole logging sources are most commonly used in mining operations: a radiation source is attached to the end of a drill head or to a wire and lowered into a borehole (wireline logging). PDMGs are used on construction sites to provide information on the density and moisture of soil to a depth of about metre.

Causes

Human error

Human causes of the accidents include:

  • Not noticing the PDMG apparatus: PDMGs are small compared to the machinery on a construction site and are often not seen or noticed, as a result they can be run over by a vehicle and damaged.
  • Not informing other workers: workers on construction sites may not notify others that there is a PDMG on site resulting in it not being identified as a radiation source.
  • Not following procedures: workers do not follow correct procedures when attaching the radiation source to the drilling rig or wire resulting in the source being lost and/or needing to be manually retrieved.

Technology factors

Technology causes of accidents include:

  • PDMG shutter mechanism: the shutter mechanism on the PDMG fails because or soil gets in and prevents the shutter from closing.
  • PDMG rod: the rod containing the radiation source, which is pushed into the ground to give a reading of density and moisture, is bent out of shape, making it difficult to retrieve the source.
  • Cable shear: in wireline logging, the cable holding the source can be sheared and come loose resulting in the source detaching from the cable. Some incidents have occurred after the cable has been weakened by corrosion.

Organisation factors

  • Oversight of site and operations: organisations fail to provide adequate oversight of workers using PDMGs or borehole/wireline logging resulting in incorrect practices being applied.
  • Not providing training and induction: organisations fail to provide staff with adequate training or induction to staff so that they are instructed on the safest methods to use the source.
  • Not providing adequate systems: organisations do not have in place adequate maintenance and inspection programs so that sources are properly functioning before being used i.e. wipe-testing the PDMG to ensure the shielding enclosing the source has not been compromised.