NEBOSH National General Certificate Physical, Electrical and Fire Hazards Syllabus

What is the difference between flashpoint and fire point?

Flashpoint is the lowest temperature at which vapour will briefly flash on ignition. Fire point is the slightly higher temperature at which the liquid produces enough vapour to support continuous (sustained) burning once ignited.

Define the lower and upper explosive (flammable) limits, LEL and UEL.

The LEL is the minimum concentration of vapour/gas in air that will ignite; below it the mixture is too lean. The UEL is the maximum concentration that will ignite; above it the mixture is too rich. Between LEL and UEL the mixture is flammable.

List the three principal methods of heat transfer that spread fire.

Conduction (through solids/metals), convection (rising hot gases and smoke spreading upward and along ceilings), and radiation (heat energy transmitted as infrared waves across space). Direct burning/flame contact is sometimes added as a fourth.

Match the European fire classes A, B, C, D, F to their fuel types.

Class A: solids (wood, paper, textiles). Class B: flammable liquids. Class C: flammable gases. Class D: metals. Class F: cooking oils and fats. Electrical fires are not a class but are described by the symbol for electrical risk.

Which extinguishing agent is most appropriate for a Class F cooking oil fire, and why not water?

A wet chemical extinguisher is used — it saponifies the oil, forming a soapy crust that smothers the fire and cools it. Water must not be used because it flashes to steam and ejects burning oil, causing a violent fireball.

State the colour code (band) and use of CO2, water, foam and dry powder extinguishers in the UK.

Water — red band, Class A. Foam — cream band, Class A and B. CO2 — black band, electrical and Class B. Dry powder — blue band, multi-purpose (A, B, C and electrical). Wet chemical — yellow/canary band, Class F.

What are the five steps of a fire risk assessment?

1) Identify fire hazards (sources of ignition, fuel, oxygen). 2) Identify people at risk. 3) Evaluate, remove/reduce risks and protect from remaining risk. 4) Record findings, prepare an emergency plan and provide training. 5) Review and update regularly.

In fire safety, distinguish between 'fire prevention' and 'fire protection'.

Fire prevention measures stop a fire starting (controlling ignition sources, fuel storage, good housekeeping). Fire protection measures limit the effects once a fire starts (detection, alarms, extinguishers, compartmentation, means of escape, sprinklers).

What is structural fire compartmentation and what is its purpose?

Compartmentation divides a building into fire-resisting compartments using fire-rated walls, floors and doors. It contains fire and smoke for a defined period, limiting spread, protecting escape routes and giving occupants time to evacuate.

Define fire resistance rating and give a typical example for a fire door.

Fire resistance is the time a structural element can withstand fire while maintaining integrity, insulation and load-bearing capacity, expressed in minutes. A common fire door is rated FD30 (30 minutes); FD60 gives 60 minutes.

What is the difference between an active and a passive fire protection measure?

Active measures require operation or movement to work (sprinklers, alarms, extinguishers, smoke vents). Passive measures work without activation by being built in (fire-resisting walls, doors, intumescent seals, compartmentation, structural protection).

State the key requirements of a satisfactory means of escape from fire.

Escape routes must be adequate in number and width, kept clear/unobstructed, lead to a place of safety, be travelable within a safe travel distance, be protected (fire-resisting where needed), well signed, and adequately lit including emergency lighting.

What is meant by 'travel distance' and why is it limited in escape design?

Travel distance is the actual distance a person must travel from any point to the nearest storey exit or final exit/place of safety. It is limited so people can escape before being overcome by heat, smoke or toxic gases; limits are shorter where only one direction of escape exists.

What is the purpose of emergency lighting on escape routes?

Emergency lighting illuminates escape routes, exit signs and fire-fighting equipment if the normal power supply fails, enabling safe evacuation. It activates automatically on mains failure and is powered by batteries or a generator.

Describe how the human ear converts sound, and which part is most vulnerable to noise damage.

Sound waves enter the outer ear, vibrate the eardrum, are transmitted by the ossicles (middle ear) to the cochlea (inner ear), where hair cells convert vibrations to nerve signals. The cochlear hair cells are most vulnerable — they are destroyed by excessive noise and do not regenerate.

Why is the decibel scale used for sound, and what does it being logarithmic imply for a 3 dB increase?

The decibel (dB) scale is logarithmic because the ear responds over a huge range of sound pressures. A $3\ \text{dB}$ increase represents a doubling of sound energy/intensity, so noise exposure roughly doubles for each 3 dB rise.

What is the difference between noise-induced hearing loss, tinnitus and temporary threshold shift?

Noise-induced hearing loss is permanent damage to cochlear hair cells from prolonged/loud noise. Tinnitus is a ringing/buzzing sensation in the ears. Temporary threshold shift is a short-term, recoverable dullness of hearing after noise exposure that can become permanent with repeated exposure.

State the lower and upper exposure action values for daily noise under the UK Control of Noise at Work Regulations.

Lower exposure action value: $L_{EP,d} = 80\ \text{dB(A)}$ (and peak $135\ \text{dB(C)}$). Upper exposure action value: $85\ \text{dB(A)}$ (and peak $137\ \text{dB(C)}$).

State the exposure limit value for daily noise under the UK Control of Noise at Work Regulations.

The exposure limit value is $L_{EP,d} = 87\ \text{dB(A)}$ daily/weekly exposure and a peak of $140\ \text{dB(C)}$. This is measured taking hearing protection into account and must not be exceeded at the ear.

At the lower and upper noise action values respectively, what employer actions are triggered?

At the lower action value ($80\ \text{dB(A)}$): provide information, training and make hearing protection available on request. At the upper action value ($85\ \text{dB(A)}$): reduce exposure by control measures, mandatory hearing protection, designate hearing protection zones, and provide health (audiometric) surveillance.

List the hierarchy of noise control measures in order of preference.

1) Eliminate/reduce at source (quieter processes/equipment). 2) Engineering controls (enclosure, silencers, damping, isolation/anti-vibration mounts). 3) Path controls (barriers, screens, acoustic absorption, distance). 4) Administrative controls (job rotation, limiting exposure time). 5) Hearing protection (PPE) as a last resort.

What is the difference between noise attenuation by enclosure and by absorption?

Enclosure (insulation) uses dense, solid barriers to block the transmission of sound energy. Absorption uses porous/soft materials lining surfaces to soak up sound energy and reduce reflected/reverberant noise. Effective control often combines both.

Distinguish between hand-arm vibration (HAV) and whole-body vibration (WBV) and a typical source of each.

HAV is transmitted to the hands/arms from vibrating tools (e.g. grinders, chainsaws, drills) and causes vascular/nerve/muscle damage. WBV is transmitted through the seat or feet (e.g. driving tractors, dumpers, fork-lifts over rough ground) and is associated with back pain.

Name the disease caused by prolonged hand-arm vibration and describe its key symptom.

Hand-Arm Vibration Syndrome (HAVS), including vibration white finger. Symptoms include blanching (whitening) of the fingers, tingling and numbness, loss of grip strength and reduced manual dexterity, especially in the cold.

State the daily exposure action and limit values for hand-arm vibration under the UK Control of Vibration at Work Regulations.

Exposure action value: $A(8) = 2.5\ \text{m/s}^{2}$ (A(8)). Exposure limit value: $A(8) = 5\ \text{m/s}^{2}$. A(8) is the daily exposure averaged (energy-equivalent) over 8 hours.

List practical control measures for hand-arm vibration exposure.

Use low-vibration tools and the right tool for the job; maintain tools (sharp/balanced); limit trigger/exposure time and job rotation; use anti-vibration mounts/handles; keep hands warm and dry; provide health surveillance; train workers to report symptoms.

Differentiate between ionising and non-ionising radiation with examples.

Ionising radiation has enough energy to remove electrons from atoms (ionise), e.g. alpha, beta, gamma, X-rays, neutrons. Non-ionising radiation lacks this energy, e.g. ultraviolet, visible light, infrared, microwaves, radio waves and lasers (lower-energy end).

Compare the penetrating power and shielding of alpha, beta and gamma radiation.

Alpha: low penetration, stopped by paper/skin (dangerous if inhaled/ingested). Beta: moderate penetration, stopped by a few mm of aluminium or perspex. Gamma (and X-rays): highly penetrating, needing thick lead or concrete to attenuate. Penetration order: $\alpha < \beta < \gamma$.

State the three principles for protecting against external ionising radiation.

Time (minimise exposure duration), Distance (increase distance from source — dose falls by the inverse square law), and Shielding (place appropriate absorbing material between source and person). Often summarised as 'time, distance, shielding'.

State the inverse square law for radiation intensity and what it means in practice.

$$I \propto \frac{1}{d^{2}}$$ Radiation intensity is inversely proportional to the square of the distance from a point source. Doubling the distance reduces the dose rate to one quarter, so increasing distance is a highly effective control.

Describe the main health effects of UV, microwave/RF and laser non-ionising radiation.

UV: skin burns (erythema), skin cancer, and arc-eye/photokeratitis (eye inflammation). Microwave/RF: deep tissue heating. Laser: localised burns and serious eye damage (retinal burns/blindness). Controls include skin and eye protection, enclosure, distance and interlocks.