NEBOSH National General Certificate Physical, Electrical and Fire Hazards Syllabus

Physical, Electrical and Fire Hazards syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Physical, Electrical and Fire Hazards in NEBOSH National General Certificate, not a summary of it.

1. 1

   Electrical Safety

   3 topics

   • Principles and Hazards of Electricity
     • Electric shock and its effects on the body
     • Burns, arcing, fire and explosion
     • Secondary effects and risk factors
   • Controlling Electrical Risk
     • Fuses, isolation and earthing
     • Residual current devices and double insulation
     • Reduced and low voltage systems
   • Inspection, Testing and Maintenance
     • User checks and formal visual inspection
     • Portable appliance testing
2. 2

   Fire Safety

   4 topics

   • Principles of Fire
     • The fire triangle
     • Classes of fire and methods of heat transfer
     • Causes of workplace fires
   • Fire Risk Assessment
     • Regulatory Reform (Fire Safety) Order 2005
     • Identifying fuel, ignition and people at risk
   • Fire Prevention and Protection
     • Controlling fuel and ignition sources
     • Structural and active fire protection
     • Fire detection and warning systems
   • Means of Escape and Emergency Evacuation
     • Travel distances and protected routes
     • Emergency lighting and assembly points
     • Evacuation procedures and drills
3. 3

   Noise and Vibration

   3 topics

   • Noise Hazards and Health Effects
     • Temporary and permanent hearing loss
     • Tinnitus and exposure action values
   • Controlling Noise Exposure
     • Noise Regulations 2005
     • Engineering controls and hearing protection zones
   • Vibration Hazards and Control
     • Hand-arm and whole-body vibration
     • Control of Vibration at Work Regulations 2005
4. 4

   Radiation

   3 topics

   • Types and Sources of Radiation
     • Ionising radiation
     • Non-ionising radiation
   • Health Effects of Radiation
   • Controlling Radiation Exposure
     • Time, distance and shielding
     • Monitoring and dose limitation

Physical, Electrical and Fire Hazards flashcards for NEBOSH National General Certificate

18 of 51 cards from the Physical, Electrical and Fire Hazards deck — real questions with worked answers.

1. State Ohm's Law and give its formula relating voltage, current and resistance.

   Ohm's Law states that current is directly proportional to voltage and inversely proportional to resistance. $$V = I \times R$$ where $V$ is voltage (volts), $I$ is current (amperes) and $R$ is resistance (ohms, $\Omega$).

2. What formula relates electrical power to voltage and current, and what are the units?

   $$P = V \times I$$ where $P$ is power in watts (W), $V$ is voltage in volts and $I$ is current in amperes. It can also be written $P = I^{2}R$.

3. List the four main hazards (effects) associated with electricity.

   Electric shock, electrical burns, fire (from arcing/overheating/faults), and explosion (ignition of flammable atmospheres or arcing in switchgear). Secondary hazards include falls caused by shock.

4. Distinguish between direct and indirect electrical contact.

   Direct contact is touching a conductor that is intentionally live (e.g. a bare live wire). Indirect contact is touching a normally dead conductive part (e.g. equipment casing) that has become live due to a fault.

5. Approximately what AC current passing through the body is regarded as the threshold for ventricular fibrillation?

   Around $50\ \text{mA}$ (and above) of AC at 50 Hz can cause ventricular fibrillation. The threshold of perception is roughly $1\ \text{mA}$; 'let-go' threshold is about $10\ \text{mA}$.

6. Why is a wet or sweaty body more dangerous in an electrical contact situation?

   Moisture lowers the body's electrical resistance, so for a given voltage a larger current flows (from $I = V/R$), increasing the severity of shock. Dry skin may be tens of $\text{k}\Omega$; wet skin can fall to around $1\ \text{k}\Omega$ or less.

7. Define an electric arc flash and state its key danger.

   An arc flash is the sudden release of energy when current jumps an air gap between conductors. It produces intense heat (radiant temperatures can exceed $19{,}000\,^{\circ}\text{C}$), UV/IR radiation, blast pressure and molten metal, causing severe burns even without direct contact.

8. What is the difference between a fuse and a circuit breaker as protective devices?

   A fuse contains a wire that melts and breaks the circuit on excess current and must be replaced after operating. A circuit breaker is a resettable switch that trips automatically on overcurrent and can be reset after the fault is cleared.

9. What does an RCD (Residual Current Device) detect and how does it protect against shock?

   An RCD monitors the difference (imbalance) between live and neutral currents. If current leaks to earth (e.g. through a person), the imbalance triggers rapid disconnection — typically tripping at $30\ \text{mA}$ within about $40\ \text{ms}$ to prevent fatal shock.

10. Explain the purpose of earthing (grounding) electrical equipment.

    Earthing provides a low-resistance path for fault current to flow safely to earth. This keeps exposed metalwork at near-zero potential and ensures enough fault current flows to operate the fuse/breaker quickly, preventing the casing staying live.

11. What is double insulation and what symbol denotes it?

    Double insulation provides two independent layers of insulation (basic plus supplementary) so no earth connection is needed; exposed metal parts cannot become live. It is marked by the Class II symbol of a square within a square (concentric squares).

12. State the principle of reduced low voltage (RLV) systems and a common value used on construction sites.

    Reduced low voltage lowers the supply voltage so that any shock is less severe. On UK construction sites portable tools commonly use $110\ \text{V}$ centre-tapped to earth, giving a maximum of $55\ \text{V}$ to earth.

13. What is a Permit-to-Work used for in electrical maintenance?

    A permit-to-work is a formal documented procedure controlling high-risk work. For electrical work it ensures isolation, proving dead, and safe access are authorised in writing, preventing re-energisation while work is in progress.

14. List the safe isolation procedure steps before working on electrical equipment.

    Identify the circuit; switch off and isolate; secure isolation (lock-off and tag); verify the testing device on a known live source; test the conductors to prove dead; re-prove the tester on the known source. Then work can begin safely.

15. What is the purpose of 'proving dead' with a test instrument before work?

    To confirm the conductors are genuinely de-energised after isolation. The tester is first checked on a known live source, used to confirm the circuit is dead, then re-checked on the live source to confirm the tester did not fail during the test.

16. Differentiate between a 'competent person' inspection and a 'user check' of portable equipment.

    A user check is a quick visual inspection by the operator before use (looking for damaged cables, casing, plugs). A competent person carries out formal visual inspection and combined inspection and testing (PAT) at defined intervals based on risk.

17. What is PAT and what does combined inspection and testing involve?

    PAT (Portable Appliance Testing) is the inspection and testing of portable electrical equipment. It combines a formal visual inspection with electrical tests such as earth continuity, insulation resistance and polarity to verify the equipment is safe.

18. State the three components of the fire triangle.

    Fuel, oxygen (or other oxidising agent), and heat (ignition source/energy). All three must be present in the right proportions for combustion; removing any one extinguishes the fire.

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