Coal Inspectorate | Alert | No.426 V 1 | 02 May 2023

Rare earth magnets

What happened?

An original equipment manufacturer (OEM) advised of an incident where an underground coal mine worker reported seeing a spark generated when a drill steel came in contact with a rare earth magnet.

As ferrite core magnets and rare earth magnets are used extensively, this Safety Alert is issued to alert industry to a potential safety hazard involving the use of rare earth magnets. 

These magnets are commonly found on equipment such as continuous miners, miner-bolters, multi-bolters and longwalls operating in hazardous environments.

How did it happen?

• The rare earth magnet was contained in a polyurethane drill steel holder.
• The magnet was exposed due to wear in the holder.
• An internationally accredited certification body was engaged by the OEM to perform extensive tests on a rare earth magnet. These tests were carried out to IEC 80079.38 Explosive atmospheres - Part 38: Equipment components in explosive atmospheres in underground mines.
• Although the magnet passed the standard tests using mild steel plate, it did not pass these tests when using hardened steel plate.
• This confirmed that a spark is generated when a steel drill hits a rare earth magnet and that this spark will ignite methane.
• A material safety data sheet for the rare earth magnet material states that:
• material is brittle and may chip if not handled with care
• magnets may spark on impact and to handle carefully in explosive atmospheres.

Recommendations

It is recommended that Site Senior Executives:

• advise all coal mine workers of potential hazards associated with rare earth magnet applications, particularly in explosion risk zones (ERZs)
• audit all equipment located in or able to enter ERZs and identify the use, application and robustness of physical protection of rare earth magnets
• visually check all applications of rare earth magnets. If any part of the rare earth magnet is exposed, remove it from service
• review inspection and maintenance regimes for rare earth magnet applications
• risk assess the continued use of rare earth magnets, consider alternative designs and the application of higher order controls.

RARE EARTH MAGNETS ARE EXTREMELY POWERFUL!

• They exhibit very strong magnetic forces attracting them to other magnets and ferromagnetic materials such as iron or steel.
• The strong force between magnets can cause severe injury when fingers and other body parts are pinched between magnets.
• Strong magnets may affect the operation of pacemakers and other implanted medical devices.
• Keep magnetised parts away from mechanical/electrical instruments which may be damaged by high magnetic fields.