Failed or Absent Defences » LTA isolation hardware » Interference with safety interlocks

24Trip Switch Defeated On Pug Mill Chamber

Click to view link.

Brief Description of Incident/Accident & Description of Consequences/Outcomes:

Recent inspections at four separate quarries identified that safety devices (trip switches) intended to stop pug mill augers rotating when the guards are removed were not operating.

Identified Root Causes:

At three of the quarries the guard trip switches on the pug mill chamber had been tied back to the set position. At the fourth quarry, fines material had settled on the trip switch and built up over a period of time preventing the switch from being activated.

Energy Type(s) Involved:

Exposure to rotating plant

Equipment Type(s):

Pug Mill

Root & Contributing Cause(s):

Interference with safety interlocks

LTA hazard identification

LTA Isolation hardware

Stated or Potential Consequence(s):

Potential Fatality

Preventative/Recommended/Accepted Steps of Risk Mitigation, Points of Interest:

All site senior executives have an obligation under section 39 of the Mining and Quarrying Safety and Health Act 1999 to ensure the risk to persons from operations is at an acceptable level. To achieve this obligation it is recommended the following be noted and addressed with respect to plant such as pug mills.

1. Assess the integrity and effectiveness of the engineering safeguards including trip switches and other safety devices.

2. Include inspection of trip switches and other safety devices in maintenance schedules.

3. Develop standard work instructions/procedures for pug mill maintenance, including the cleaning of the pug mill chamber.

4. Ensure all personnel are aware of the hazards associated with pug mills.

All persons have an obligation under section 36 of the Mining and Quarrying Safety and Health Act 1999 not to do anything wilfully or recklessly that might adversely affect the safety and health of someone else at the mine.

Defeating safety devices and controls is a dangerous shortcut that has the potential to kill. If a worker comes across such a situation, he should report it immediately.

EMESRT Risk(s):

Entanglement in machine parts

ISOLgate Checklist(s):

Download Entanglement in machine parts Checklist.


Queensland Government Department of Employment, Economic Development and Innovation (DEEDI)


Here are the results.


Reference Type:

Safety Alert #91

EMESRT Risk(s):

Entanglement in machine parts

Mine Type:

Surface Mine


Potential & Kinetic - Mechanical > Moving machine part(s)





Australia, Queensland

©2020 ISOLgate