Occupational Health, Safety and Environment
Core Concepts
Candidates must understand electrical safety principles: shock hazards (current path, duration, body resistance), arc flash and blast, lockout/tagout (LOTO), personal protective equipment (PPE), and safe isolation procedures. Know the effects of current on the body (e.g., 30 mA can cause respiratory paralysis; 50 mA can cause ventricular fibrillation). Understand protective measures: earthing, fuses, circuit breakers, RCDs (residual current devices), and double insulation. Environmental considerations include proper disposal of lamps (fluorescent tubes contain mercury), batteries, and electronic waste; recycling of cables and metals; and energy efficiency practices.
Traps in Questions
- Confusing isolation with switching off: isolation requires physical disconnection and locking, not just pressing a button.
- PPE selection: rubber gloves are not sufficient for high voltage; insulated tools and mats are needed.
- First aid for electric shock: never touch the casualty if still in contact with live parts; isolate first.
- Fire classes: electrical fires are Class C (or E in some systems); use CO2 or dry powder, never water.
- Environmental: fluorescent lamps are hazardous waste, not general refuse.
Worked Example / Rule of Thumb
Rule of thumb: For low-voltage safe isolation, follow the sequence: identify, isolate, lock/tag, prove dead with an approved voltage tester, and re-test the tester. For shock risk, remember: 30 mA RCD protects people; 100 mA or 300 mA RCDs are for fire protection. Example: A 30 mA RCD must trip within 300 ms at rated residual current. If a question asks for maximum disconnection time for a 30 mA RCD, answer 300 ms.