This week's alerts have generated a lot of questions about pedestal and bench grinder safety measures. I will try and explain and show the OSHA requirements and why they are what they are...
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This week a worker was killed while using a pedestal grinder. Preliminary investigations indicate this was an exploding wheel accident. Here is my Incident Alert Summary on the incident:
PEDESTAL GRINDING WHEEL FAILURE FATALITY Man dies in accident at Surrey plant (a worker is dead after an accident at a manufacturing plant at around 2 p.m. - an initial report indicated the worker had been operating a pedestal grinder when the wheel "exploded" and critically injured him - employees at the plant say there was no explosion, but rather a piece of the machinery came loose and struck him - the worker was taken to hospital with serious injuries but died a short time later - he is estimated to be around 50 years old) [Click Here to subscribe to my Incident Alerts]
These grinding wheels can turn at 4,000 RPM and when they have a catastrophic failure they are much like a shotgun going off (hence some folks would call it an explosion!). The two guards on these fixed style grinders are there to prevent a failure of the wheel AND to protect the worker operating the grinder.
Below you will see the OSHA requirements for these grinders, but first let me try and simplify these OSHA requirements. The tool rest plays a CRITICAL ROLE in preventing the #1 cause of wheel failure. Workers use the grinder with the tool rest positioned TOO FAR AWAY from the wheel and this allows the part the worker is grinding to become lodged between the wheel and the tool rest. When this happens, the wheel will experience a catastrophic failure. When this failure occurs, the Upper Peripheral Guard (known as the Tongue Guard) aids in preventing the wheel from being projected directly out onto the worker (NOTE: the wheels spin toward the front of the grinder). Remember, these wheels can operate at 4,000 rpm and without the peripheral guard IN PLACE and PROPERLY ADJUSTED there is NOTHING between the exploding wheel and the worker! Just something to consider when walking by a pedestal or bench grinder the next time - it takes ONLY 5 seconds to check! Even if you do not have the fancy tool, I was always trained to use another precisely calibrated tool...a #2 pencil or pen!!! If the pen will fit between either device then they are NOT PROPERLY adjusted and the grinder poses a significant hazard if used in this condition.
OSHA requires the following on bench and pedestal grinders:
1910.215(a)(4) Work rests. On offhand grinding machines, work rests shall be used to support the work. They shall be of rigid construction and designed to be adjustable to compensate for wheel wear. Work rests shall be kept adjusted closely to the wheel with a maximum opening of one-eighth inch to prevent the work from being jammed between the wheel and the rest, which may cause wheel breakage. The work rest shall be securely clamped after each adjustment. The adjustment shall not be made with the wheel in motion.
1910.215(b)(9) Exposure adjustment. Safety guards of the types described in Subparagraphs (3) and (4) of this paragraph, where the operator stands in front of the opening, shall be constructed so that the peripheral protecting member can be adjusted to the constantly decreasing diameter of the wheel. The maximum angular exposure above the horizontal plane of the wheel spindle as specified in paragraphs (b)(3) and (4) of this section shall never be exceeded, and the distance between the wheel periphery and the adjustable tongue or the end of the peripheral member at the top shall never exceed one-fourth inch.
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What a grinder is NOT suppose to look like!!!!
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Tool rest too far away from wheel and no peripheral (tongue) guards at all!!!!
A GREAT and RELIABLE source for more information is the Canadian Centre for Occupational Health & Safety page on "Use of Bench and Pedestal Grinders".
OSHA also has a GREAT safety inspection checklist that can be used. Click Here
A partial list of accidents involving grinders from OSHA's Database is also available.