Occupational Safety, Health and Environment in Machine Shops
What this domain tests
Shop-floor safety, fire prevention, PPE, statutory duties, occupational disease and environmental control. Expect at least one numerical item, usually noise dose or ventilation.
Core rules
- Hierarchy of control: eliminate, substitute, engineer out (guards, local exhaust), administrative (rotation, training), PPE last. PPE is the final barrier, never the first.
- Guarding: fixed guards on belts, gears and shafts; interlocked gates on access doors; two-hand control on presses. Isolate and lock-out/tag-out before removing any guard.
- Fire classes and media: A solids – water or CO2; B flammable liquids – foam, CO2 or dry powder; C gases – dry powder or CO2; D metals – special dry powder, never water; live electrical – CO2 or dry powder, never water or foam.
- Noise: 90 dB(A) for an 8-hour day with a 3 dB exchange rate, so 93 dB(A) is permitted for 4 hours only.
- Grinding, welding and painting need local exhaust ventilation; a dust mask does not stop solvent vapour.
- Never use compressed air on skin or clothing.
Worked example
A grinder operator is exposed to 93 dB(A) for a 6-hour shift. At a 3 dB exchange rate the permitted exposure at 93 dB(A) is 4 hours, so the dose is 6/4 = 150 %, above the 100 % limit. Correct response: engineering control first (silenced machine, acoustic enclosure), hearing protection as an interim measure, and audiometry for the operator.
Traps that cost marks
- Water on a solvent (Class B) or live electrical fire.
- Treating PPE as the primary control instead of the last resort.
- Using a linear estimate instead of the 3 dB halving rule for noise.
- Assuming a dust mask protects against solvent vapour – it does not.