WorkCover Queensland has issued a safety alert to highlight the risks associated with removing guards and using incorrect discs on angle grinders.
The safety alert follows an incident involving a Queensland worker who was killed while operating a 230mm (9 inch) angle grinder last month.
The incident happened when part of a broken disc struck his chest. The high impact of the projectile apparently caused fatal internal injuries.
In another incident the disc jammed and the angle grinder kicked back and cut a worker's wrist.
A major contributing factor is the use of cutting discs that are too large for the angle grinder, says WorkCover Queensland.
“In some cases the guards have been removed and the grinder fitted with a 14 inch (356 mm) cut-off disc,” it claims.
Cutting discs are usually designed for a maximum outside edge speed (i.e. peripheral speed) of about 70m/sec (250 km/h).
Larger angle grinders are manufactured with lower revolutions per minute (RPM) speeds than smaller angle grinders, so that the edge speed of the disc always remains around 70 m/s.
Fitting a 14 inch (356mm) cut-off disc to a 9 inch (230 mm) angle grinder will increase the edge speed excessively to at least 120 m/s (430 km/h).
Discs are not designed for the higher speed, and if used, risk the possibility of the disc shattering and striking the user and others.
Guards should be provided and used on all power tools where there is a risk of the disc ejecting, disintegrating or cutting the worker.
If the guard has been removed:
· There is nothing to stop the broken pieces hitting the user
· The user's hand will be closer to the unguarded moving blade
· There is also a greater risk of the blade being damaged when the angle grinder is put down and the weight of the grinder is resting directly on the disc.
Another factor that increases the risk of disc failure is when the central disc hole size is too large for the spindle flange on the angle grinder.
As the disc diameter increases so will the hole size. For example, the hole size of a 14 inch (356 mm) cut-off wheel is typically 25.4 mm compared to 22.3 mm on a 9 inch (230 mm) cutting disc.
If the disc hole is too big for the spindle flange, the disc may be off centre, become unbalanced, vibrate excessively and rapidly lead to it shattering.
WorkCover Queensland offers the following safety tips:
· Use the angle grinder with the correct guard supplied by the manufacturer.
· Fit the right sized disc that has a hole matching the spindle flange.
· Use the tightening tool supplied by the grinder manufacturer to tighten the disc. The use of another device (i.e. punch and hammer) can damage the disc and grinder.
· Hold the angle grinder with both hands ensuring the side handle is inserted on the side of the unit that gives the best grip for the work activity.
· Use a grinding disc for grinding. Grinding with a cutting disc damages the disc and increases the likelihood of the disc breaking during use.
· Ensure the maximum RPM disc speed marked on the disc is higher than the maximum speed of the angle grinder.
· Ensure damaged discs are thrown out and not re-used.
· Allow the grinder to run to speed before cutting or grinding.