Abrasive Wheels Training Certificate Hazards of Abrasive Wheels — Questions and Answers
Question 1: What is the primary cause of abrasive wheel burst, which is the most serious hazard?
- Overspeed — operating the wheel above its maximum RPM rating causes centrifugal forces to exceed the bond's tensile strength (Correct answer)
- Excessive downward pressure on the wheel during grinding
- Coolant contamination of the grinding wheel bond
- Running the wheel in the wrong direction of rotation
Correct answer: Overspeed — operating the wheel above its maximum RPM rating causes centrifugal forces to exceed the bond's tensile strength
Wheel burst (disintegration) occurs when centrifugal forces generated by rotation exceed the tensile strength of the bonding material. The primary cause is operating above the maximum marked RPM. Other causes include mechanical damage, incorrect mounting, and side loading. Wheel fragments can reach lethal velocities.
Question 2: What energy does a bursting abrasive wheel release, and why is this so dangerous?
- Kinetic energy proportional to mass and the square of peripheral velocity; fragments can travel at several hundred metres per second (Correct answer)
- Only thermal energy from friction — fragments are too light to cause serious injury
- Potential energy only if the wheel is mounted at height
- Chemical energy from the abrasive reaction with the workpiece
Correct answer: Kinetic energy proportional to mass and the square of peripheral velocity; fragments can travel at several hundred metres per second
A 125mm angle grinder disc rotating at 11,000 RPM stores significant kinetic energy. When it bursts, fragments are propelled outward at high velocity — potentially hundreds of metres per second. The combination of mass and velocity gives fragments lethal penetrating power sufficient to pierce workwear and cause fatal injury.
Question 3: What is the hazard of 'contact' with an abrasive wheel?
- Severe laceration, degloving, or amputation from accidental contact with the rotating abrasive surface (Correct answer)
- Only superficial skin abrasion in brief contact
- Burns from the grinding sparks rather than the wheel surface
- Only a hazard during wheel mounting, not during operation
Correct answer: Severe laceration, degloving, or amputation from accidental contact with the rotating abrasive surface
Contact with a rotating abrasive surface causes immediate severe injury. The abrasive rapidly removes skin, tissue, and bone on contact. High-speed contact with a 125mm disc at 11,000 RPM causes injuries comparable to a high-speed circular saw — amputations and severe lacerations are common outcomes of unguarded wheel contact.
Question 4: What type of vibration hazard is associated with extended use of angle grinders?
- Hand-arm vibration syndrome (HAVS) causing permanent damage to blood vessels, nerves, and joints in the hands and arms (Correct answer)
- Only acute fatigue with no long-term effects
- Only affects workers over 60 years of age
- Vibration only causes short-term numbness that resolves within 24 hours
Correct answer: Hand-arm vibration syndrome (HAVS) causing permanent damage to blood vessels, nerves, and joints in the hands and arms
Hand-arm vibration syndrome (HAVS) — including vibration white finger (VWF) — is caused by prolonged exposure to hand-transmitted vibration from power tools including angle grinders. It is irreversible and progressive, causing permanent damage to peripheral blood vessels, nerves, and tendons, leading to pain, disability, and loss of tactile sensation.
Question 5: What fire and explosion hazard is created by grinding sparks?
- Sparks can travel several metres and ignite flammable materials, liquids, vapours, and combustible dusts in the vicinity (Correct answer)
- Sparks only ignite materials that are directly adjacent to the grinding operation
- Sparks from abrasive grinding are too low temperature to ignite materials other than paper
- Only dry wood is at risk of ignition from grinding sparks
Correct answer: Sparks can travel several metres and ignite flammable materials, liquids, vapours, and combustible dusts in the vicinity
Grinding sparks are incandescent metal particles at temperatures of several hundred to over 1,000°C. They can travel 3–10 metres from the grinding point and ignite flammable liquids, gases, vapours, combustible dusts, and dry materials such as wood shavings and insulation. A hot work permit system manages this risk.
Question 6: What health hazard is caused by inhaling grinding dust and fume?
- Respiratory diseases including occupational asthma, fibrosis, and metal fume fever depending on the workpiece material (Correct answer)
- Only temporary irritation with no long-term health effects
- Hazard is limited to workers with pre-existing asthma
- Only a hazard when grinding stainless steel — mild steel presents no risk
Correct answer: Respiratory diseases including occupational asthma, fibrosis, and metal fume fever depending on the workpiece material
Grinding fumes and dust include metal particles, metal oxides (including hexavalent chromium from stainless steel — a known carcinogen), non-metallic abrasive dust, and bonding material. Inhalation can cause occupational asthma, metal fume fever, lung fibrosis, and occupational cancer. LEV (local exhaust ventilation) and RPE are required controls.
