Working of a Lead Acid Battery

A lead acid battery is a secondary (storage) cell that converts chemical energy into electrical energy and can be recharged. It consists of:

• Positive plate (anode in discharge): lead dioxide (PbO₂)
• Negative plate (cathode in discharge): spongy lead (Pb)
• Electrolyte: dilute sulphuric acid (H₂SO₄, about 35%)

Discharging (when the battery supplies current):

• At the negative plate, lead is oxidised and releases electrons: Pb + SO₄²⁻ → PbSO₄ + 2e⁻
• At the positive plate, PbO₂ takes up electrons and is reduced: PbO₂ + SO₄²⁻ + 4H⁺ + 2e⁻ → PbSO₄ + 2H₂O
• Overall reaction: Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O
• Electrons flow through the external circuit from the negative to the positive terminal, so current flows from positive to negative. Both plates become coated with lead sulphate (PbSO₄) and the acid becomes weaker (density falls).

Charging (when an external d.c. source is connected):

• The reactions reverse. PbSO₄ on both plates is converted back to Pb (negative) and PbO₂ (positive), and the acid is regenerated and becomes concentrated again.
• Overall reaction: 2PbSO₄ + 2H₂O → Pb + PbO₂ + 2H₂SO₄

Thus the battery can be used again and again by recharging. Each cell gives about 2 V; six cells in series give a 12 V battery.

Uses in Household

1. Inverter / backup power — supplies electricity during load-shedding or power cuts to run lights, fans and TV.
2. Solar home systems — stores the electricity generated by solar panels for use at night.
3. Emergency lights and torch — provides power for emergency lighting.
4. Starting motor vehicles — used in cars, motorcycles and tractors for ignition and lighting.
5. UPS for computers and routers — gives backup power to electronic devices.

Ohm's Law

Ohm's law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided the physical conditions (temperature, length, area of cross-section and material) remain constant.

If $V$ is the potential difference across a conductor and $I$ is the current flowing through it, then

$V \propto I \quad \Rightarrow \quad V = IR$

where $R$ is the resistance of the conductor. In SI units, $V$ is in volt, $I$ in ampere and $R$ in ohm ($\Omega$).

Limitations of Ohm's law

1. Valid only for ohmic conductors: It does not hold for non-ohmic devices such as diodes, transistors, thermionic valves, semiconductors and electrolytes, where the $V$–$I$ graph is not a straight line.
2. Temperature must remain constant: If the temperature of the conductor changes, resistance changes and the relation $V = IR$ no longer gives a constant $R$.
3. Not applicable to gas discharge: Ohm's law fails for conduction through gases and for vacuum tubes.
4. Not valid for very high potential difference or very low temperature: In such conditions the linear relation breaks down (e.g. superconductors have zero resistance).
5. Only for a given length of conductor: The law applies to a definite portion of a circuit; it cannot be applied directly to the whole circuit containing sources of emf without proper sign conventions.

Operation of a Diesel Power Plant

A diesel power plant works on the diesel cycle (constant-pressure cycle) and converts the chemical energy of diesel fuel into electrical energy. Its main components are the diesel engine, air intake system, fuel supply system, cooling system, lubrication system, exhaust system, starting system, and generator (alternator).

Step-by-step operation:

1. Air intake: Atmospheric air is drawn into the engine cylinder through the air filter during the suction stroke of the piston.
2. Compression: The piston moves upward and compresses the air to a high pressure (about 30–40 bar) and high temperature (about 500–600 °C). This is the compression stroke.
3. Fuel injection: At the end of compression, finely atomized diesel fuel is injected into the hot compressed air through the fuel injector. The fuel ignites automatically due to the high temperature — no spark plug is needed (hence it is a compression-ignition engine).
4. Power (expansion) stroke: The burning gases expand rapidly and push the piston downward, producing mechanical work. This is the only stroke that produces power.
5. Exhaust stroke: The burnt gases are pushed out through the exhaust valve and discharged to the atmosphere through the silencer.
6. Energy conversion: The reciprocating motion of the piston is converted into rotary motion by the crankshaft. The crankshaft is coupled to the alternator, which converts mechanical energy into electrical energy.
7. Auxiliary systems: The cooling system (water or air) removes excess heat from the engine; the lubrication system reduces friction between moving parts; the fuel system supplies and injects fuel; and the starting system (battery or compressed air) starts the engine.

Advantages: Simple design, quick starting, low initial cost, needs less cooling water, can be located anywhere, and is suitable for standby and small-scale power generation.

Disadvantages: High fuel cost, high maintenance cost, limited capacity (usually up to about 5 MW), noisy operation, and shorter life compared to steam plants.

No Load Test (Open Circuit Test) on a Transformer

Circuit connection: The low-voltage (LV) winding is kept open and the high-voltage (HV) winding is connected to a variable AC supply through an ammeter, a voltmeter and a wattmeter. The voltmeter measures the applied voltage, the ammeter measures the no-load current and the wattmeter measures the no-load power.

Procedure:

1. The LV winding is left open-circuited (no load connected).
2. A rated voltage at rated frequency is applied to the HV winding using the variac (variable AC supply).
3. The readings of the voltmeter (V₀), ammeter (I₀) and wattmeter (W₀) are noted.
4. Since the LV side is open, only a small no-load (excitation) current flows through the primary. This current supplies the iron losses (hysteresis and eddy current losses) and a very small copper loss in the primary.
5. The copper loss being negligible (I₀ is very small), the wattmeter reading gives practically the iron loss (core loss) of the transformer:

$W_0 = P_i \text{ (iron loss)}$

6. The no-load power factor is calculated as:

$\cos\phi_0 = \frac{W_0}{V_0 I_0}$

7. From these readings the magnetising (shunt) branch parameters — R₀ and X₀ — are found:

$R_0 = \frac{V_0^2}{W_0}, \qquad I_w = I_0\cos\phi_0, \qquad I_\mu = I_0\sin\phi_0$

$X_0 = \frac{V_0}{I_\mu}$

Main purpose:

The main purpose of the no-load test is to determine the iron loss (core loss) of the transformer and the no-load current and no-load power factor, from which the parameters of the shunt (magnetising) branch of the equivalent circuit (R₀ and X₀) are obtained. Since iron loss is practically constant at all loads at rated voltage, this test gives the constant loss of the transformer, which is needed to calculate its efficiency.

(a) Single line diagram of a typical distribution system — 4 marks

A typical distribution system consists of the following stages in sequence:

1. Generating station — produces electrical power at 11 kV (or 6.6 kV).
2. Primary transmission — step-up transformer raises voltage to 132 kV / 220 kV / 400 kV; power carried by 3-phase 3-wire overhead lines to distant load centres.
3. Secondary transmission — step-down transformer reduces voltage to 33 kV; carried by 3-phase 3-wire lines to substations near towns.
4. Primary distribution — step-down to 11 kV; carried by 3-phase 3-wire lines along main roads.
5. Secondary distribution — distribution transformer reduces to 400 V (3-phase 4-wire); supplies consumers at 230 V single-phase and 400 V three-phase.

   ┌──────────────┐
   │  Generating  │  11 kV
   │   Station    │
   └──────┬───────┘
          │  ▲ Step-up transformer (11/132 kV)
          ▼
   ═══════════════════  Primary transmission  (132 kV, 3-φ, 3-wire)
          │
          ▼  Step-down transformer (132/33 kV)
   ═══════════════════  Secondary transmission (33 kV, 3-φ, 3-wire)
          │
          ▼  Step-down transformer (33/11 kV)
   ═══════════════════  Primary distribution  (11 kV, 3-φ, 3-wire)
          │
          ▼  Distribution transformer (11/0.4 kV)
   ═══════════════════  Secondary distribution (400 V, 3-φ, 4-wire)
          │
   ┌──────┴──────┬──────────┐
   ▼             ▼          ▼
 Consumer      Consumer   Consumer
 (230 V, 1-φ)  (230 V)    (400 V, 3-φ)

(b) Circuit diagram of ring main type distribution system — 1 mark

In a ring main system the distributor forms a closed loop around the load area. Each consumer is fed from the nearest point on the ring through a distribution transformer, and the ring is energised at one point (or two) by the substation.

              Substation (11 kV)
                    │
        ┌───────────┴───────────┐
        │                       │
   ┌────┴────┐             ┌────┴────┐
   │  CB1    │             │  CB2    │
   └────┬────┘             └────┬────┘
        │                       │
   ┌────┴────┐             ┌────┴────┐
   │   T1    │             │   T2    │
   └────┬────┘             └────┬────┘
        │                       │
   ┌────┴────┐             ┌────┴────┐
   │   T3    │             │   T4    │
   └────┬────┘             └────┬────┘
        │                       │
        └───────────┬───────────┘
                    │
              (ring closed)

Where CB = circuit breaker, T1, T2, T3, T4 = distribution transformers feeding consumers at 400 V / 230 V. The ring is normally operated with the loop closed so that each consumer can be supplied from two directions; if a fault occurs on one section, that section is isolated by opening the two nearest isolators and supply continues from the other side. This gives higher reliability and better voltage regulation than a radial system.

A fuse and an MCB (Miniature Circuit Breaker) are both protective devices used to break a circuit when excess current flows, but they differ in construction, operation and reusability.

Comparison:

Conclusion: For domestic and industrial installations, the MCB is preferred because it is reusable, more accurate, faster and safer, though the fuse is still used where cheap, one-time protection is sufficient.

Necessity of Earthing in Power System

Earthing (or grounding) means connecting the non-current-carrying metallic parts of electrical equipment and the neutral point of the system to the general mass of earth through a low-resistance conductor.

Necessity:

1. Safety of human life: If a live conductor touches the metallic body of a machine, the body becomes charged. With proper earthing, the fault current flows to earth and the body remains at earth potential, so a person touching it is not electrocuted.

2. Protection of equipment: Earthing provides a low-resistance path for fault current, so the protective device (fuse, MCB, relay) operates quickly and the equipment is isolated before damage occurs.

3. Voltage stabilization: Earthing the neutral keeps the phase-to-neutral voltage constant and prevents the potential of the neutral from rising during unbalanced loading.

4. Prevention of fire and explosion: Leakage currents are safely discharged to earth, avoiding sparking that could ignite inflammable gases or materials.

5. Lightning and surge protection: Earthing gives a discharge path for lightning strokes and switching surges, protecting insulators, transformers and transmission lines.

6. Reliable operation of protective relays: A definite earth-fault current path is required for earth-fault relays to sense the fault and trip the circuit breaker.

---

Working of a Lightning Arrester

A lightning arrester is a protective device installed between the line and earth to discharge abnormal high-voltage surges (due to lightning or switching) to earth and then restore normal operation.

Construction: It consists of a spark gap in series with a non-linear resistor (valve element, e.g. thyrite or silicon carbide), enclosed in a porcelain housing. One terminal is connected to the line and the other to earth.

Working:

1. Normal condition: The line voltage is below the breakdown value of the gap. The gap acts as an insulator, so no current flows to earth and the arrester behaves as an open circuit.

2. Surge condition: When a lightning surge or switching overvoltage reaches the arrester, the voltage exceeds the spark-over voltage of the gap. The gap breaks down and becomes conducting.

3. Discharge to earth: The surge current flows through the gap and the non-linear resistor to earth. The non-linear resistor has the property that its resistance decreases sharply as voltage rises, so it offers a very low-resistance path and discharges the surge quickly without allowing the voltage to rise dangerously.

4. Sealing (resealing): As soon as the surge is discharged, the voltage falls to normal. The resistance of the valve element increases sharply at low voltage, so the current through the arrester becomes very small (a few milliamperes) — below the value needed to maintain the arc. The arc at the gap is extinguished and the arrester is resealed, ready for the next surge.

Thus the arrester acts as a safety valve: it conducts only during overvoltage and remains an insulator at normal voltage, protecting the line and equipment from lightning surges.

Different methods of starting of an induction motor:

1. Direct-on-line (DOL) starting
2. Star-delta starting
3. Autotransformer starting
4. Rotor resistance starting (for slip-ring motors)
5. Stator resistance/reactance starting

(1) Direct-on-line (DOL) starting: The motor is connected directly to the full supply voltage through a contactor and overload relay. Starting current is very high (about 5–7 times full-load current), so it is used only for small motors (up to about 5 kW).

(2) Star-delta starting: The stator winding is first connected in star (so each phase gets $V_L/\sqrt{3}$) and then changed to delta when the motor picks up speed. Starting current and torque are reduced to one-third of the DOL values. Used for motors designed to run in delta.

(3) Autotransformer starting: A tap on an autotransformer applies a reduced voltage (say 50–80% of line voltage) to the stator at start. Since torque varies as the square of voltage, starting torque is reduced. Tappings allow selection of starting current. Used for large motors.

(4) Rotor resistance starting: Used for slip-ring (wound-rotor) motors. External resistance is inserted in the rotor circuit at start and gradually cut out. It reduces starting current and at the same time gives high starting torque. Most suitable for high-inertia loads.

(5) Stator resistance/reactance starting: A resistance or reactor is inserted in series with the stator winding, reducing the voltage at the motor terminals during starting. It is simple and cheap but gives poor torque and wastes power in the resistor. Used for small and medium motors.

Explanation of each starting method:

(a) Direct-on-line (DOL) starter: A triple-pole switch (or contactor) connects all three phases directly to the stator. At start, the rotor is at standstill, slip $s = 1$, so rotor e.m.f. and rotor current are maximum. Hence the stator draws a very large current, $I_{st} \approx 5$ to $7$ times $I_{fl}$. Starting torque is also high. Advantages: simple, cheap, high starting torque. Disadvantages: heavy current surge causes voltage dip in the supply line. Used for small motors only.

(b) Star-delta starter: At starting the stator phases are connected in star, so phase voltage $= V_L/\sqrt{3}$. The phase current is reduced by $1/\sqrt{3}$ and the line current by $1/3$ compared with delta connection. After the motor attains about 80% of full speed, a changeover switch connects the winding in delta. Starting torque becomes $1/3$ of the DOL value. It needs a motor whose winding can be delta-connected and having six terminals. Cheap and widely used for medium motors.

(c) Autotransformer starter: An autotransformer with tappings (usually 50%, 65%, 80%) supplies reduced voltage to the motor. If the tapping ratio is $x$, then starting current from the line $= x^2 I_{sc}$ and starting torque $= x^2 T_{sc}$. Thus both current and torque are reduced. The motor is switched to full voltage when it speeds up. It is costly but gives a good starting torque per ampere of line current. Used for large squirrel-cage motors.

(d) Rotor resistance starter (slip-ring motor): The slip-ring rotor is connected through brushes to external star-connected resistances. At start the full external resistance is in the rotor circuit, which increases rotor circuit impedance, reduces rotor current and hence stator current. At the same time the rotor power factor improves, so starting torque is high. The resistances are gradually cut out as the motor accelerates. Finally the slip rings are short-circuited and brushes lifted. Best method for loads requiring high starting torque.

(e) Stator resistance/reactance starter: A resistance or an iron-cored reactor is connected in series with each stator phase. The voltage across the motor terminals is reduced, so starting current falls. Since torque $\propto V^2$, torque also falls sharply. The resistance method wastes $I^2R$ power; the reactor method is more efficient. Used for small and medium squirrel-cage motors where the supply is weak.

Voltmeter is connected in parallel with the circuit component whose potential difference is to be measured.

Reasons:

1. To measure potential difference: A voltmeter measures the potential difference (voltage) between two points. The potential difference across a component is the difference in electric potential between its two terminals. To measure this difference, the voltmeter must be connected across (in parallel with) those two points.

2. High resistance: A voltmeter has a very high resistance (ideally infinite). When connected in parallel, it draws a negligible current from the circuit, so it does not disturb the original current flowing through the component. Thus the reading obtained is accurate.

3. If connected in series: A voltmeter connected in series would carry the full circuit current. Because of its very high resistance, it would greatly reduce the current in the circuit (almost to zero), and the circuit would not work properly. Moreover, it would measure only the small voltage drop across itself, not the voltage across the component.

Hence, a voltmeter is always connected in parallel.

Connection and measuring procedure of an insulation tester (megger)

Connection:

1. Isolate the circuit — switch off the supply, remove fuses, and discharge the circuit to be tested (especially capacitors and long cables).
2. Disconnect the equipment — separate the winding/cable under test from earth and from other circuits so that only the part to be tested is connected.
3. Identify the terminals — the megger has three terminals: Line (L), Earth (E), and Guard (G).
4. Connect Line (L) to the conductor whose insulation is to be tested (e.g. winding terminal or cable core).
5. Connect Earth (E) to the earth/body of the equipment or to the other conductor (e.g. earthed frame or sheath).
6. Connect Guard (G) only when surface leakage current is to be eliminated — it is connected to the guard ring/insulating surface between L and E.
7. Ensure all connections are tight, clean and dry, and that the test leads are well insulated and kept apart from each other.

Measuring procedure:

1. Set the megger to the required test voltage (500 V, 1000 V, 2500 V etc. as per the equipment rating).
2. Check the megger itself: with L and E open, operate it — the pointer should read infinity (∞); short L and E — the pointer should read zero.
3. Connect the leads as described above and keep the equipment terminals clear of the operator's hands.
4. Rotate the hand-crank generator at the rated speed (about 120 rpm) steadily, or switch on the motorised/battery-operated megger.
5. Maintain the test voltage for one minute (for standard insulation resistance measurement) and note the reading on the scale.
6. Record the insulation resistance value in mega-ohms (MΩ) at the end of one minute.
7. For polarisation index (PI), note the reading at 1 minute and at 10 minutes; PI = R₁₀ min / R₁ min.
8. After the test, discharge the circuit by shorting L to E through a discharge resistance, then remove the leads.
9. Compare the measured value with the minimum permissible value (generally 1 MΩ per kV of rated voltage + 1 MΩ, or as per IS/IEC standards) to decide whether the insulation is healthy.

Precautions: Never test a live circuit; always discharge after testing; keep the megger leads separate; do not touch the terminals during the test; and record the temperature since insulation resistance varies with temperature.

Causes of Electric Shock (3 marks)

1. Direct contact with live (bare) conductors — touching exposed wires, terminals or busbars that are not insulated.
2. Defective or damaged insulation — old, cracked, burnt or worn-out insulation on wires, cables and appliances allows current to leak to the body.
3. Faulty earthing (improper or absent grounding) — if the metal body of a machine, refrigerator, iron or motor is not properly earthed, it becomes live on insulation failure and gives a shock on touch.
4. Overloading and short circuits — excess current heats and damages insulation, exposing live conductors.
5. Carelessness and unsafe working practice — working on a live line without switching off, without rubber gloves, rubber mats or insulated tools; using wet hands or standing on a wet floor.
6. Use of substandard materials and equipment — low-quality wires, plugs, sockets, switches and lack of fuses/MCBs.
7. Lack of maintenance and poor housekeeping — loose connections, damaged plugs, temporary wiring, water leakage near electrical fittings.
8. Lightning and static charge — high-voltage surges and static electricity, especially in tall structures and dry conditions.

Measures to Minimize the Causes (2 marks)

1. Switch off the supply and use a lock-out/tag-out system before working on any line or equipment.
2. Use personal protective equipment — rubber gloves, rubber-soled shoes, insulated tools, safety helmet and rubber mats.
3. Provide proper earthing to all metal bodies of electrical equipment and use earth-leakage circuit breakers (ELCB/RCCB).
4. Use good-quality, properly insulated wires, cables and fittings, and keep insulation in good condition by regular inspection and replacement.
5. Install fuses, MCBs and proper protective devices to clear overloads and short circuits quickly.
6. Avoid water and wet conditions near electrical installations; never touch switches or appliances with wet hands.
7. Follow safety rules and give safety training to workers; display warning boards and keep children away from live parts.
8. Do regular maintenance of wiring, plugs and appliances, and use only standard, ISI-marked equipment.

Points to be considered for preventive maintenance of generator (5 marks)

1. Regular inspection schedule — Prepare a daily, weekly, monthly and yearly maintenance calendar and follow it strictly as per the manufacturer's manual.

2. Lubrication and oil check — Check engine oil level daily, change oil and oil filter at specified intervals, and grease bearings and moving parts regularly.

3. Fuel system care — Keep the fuel tank clean and full to avoid condensation, drain water and sediment from the fuel filter, and replace fuel filters periodically.

4. Cooling system — Check coolant/water level, clean the radiator and cooling fins, check the fan belt tension, and use proper anti-freeze or soft water to prevent scaling.

5. Battery maintenance — Keep terminals clean and tight, check electrolyte level and specific gravity, and maintain full charge so that the generator starts immediately during power failure.

6. Air and exhaust system — Clean or replace the air filter, check for leakage in the exhaust pipe, and ensure proper ventilation of the generator room.

7. Electrical parts check — Inspect wiring, connections, brushes, slip rings, AVR, and control panel; tighten loose terminals and test insulation resistance.

8. Test run — Run the generator (on load if possible) at regular intervals to keep it in working condition and to confirm automatic changeover operation.

9. Safety and cleanliness — Keep the generator room dry, clean and free from dust and combustible materials; keep fire extinguishers ready and ensure proper earthing.

10. Record keeping — Maintain a log book of running hours, fuel consumption, repairs and replacements so that maintenance is done at the right time.

Single-Phase Residential Wiring Diagram with Protection Scheme

Neat Sketch (Schematic Diagram)

        SERVICE ENTRANCE (From NEA Pole)
                    │
              ┌─────┴─────┐
              │  Energy   │   ← kWh Meter
              │   Meter   │
              └─────┬─────┘
                    │  (Phase - Red)
                    │  (Neutral - Black)
                    │  (Earth - Green)
                    │
        ┌───────────┴───────────┐
        │      MAIN BOARD       │
        │  (Distribution Box)   │
        │                       │
        │  ┌─────────────────┐  │
        │  │  Main Switch /  │  │  ← DP MCB / Main Switch
        │  │   DP MCB (63A)  │  │
        │  └────────┬────────┘  │
        │           │           │
        │  ┌────────┴────────┐  │
        │  │   ELCB / RCCB   │  │  ← 30 mA Sensitivity
        │  │   (30 mA, 63A)  │  │
        │  └────────┬────────┘  │
        │           │           │
        │  ┌────────┴────────┐  │
        │  │   Bus Bar (P)   │  │
        │  │   Bus Bar (N)   │  │
        │  │   Bus Bar (E)   │  │
        │  └──┬──┬──┬──┬──┬──┘  │
        └─────┼──┼──┼──┼──┼─────┘
              │  │  │  │  │
      ┌───────┘  │  │  │  └────────┐
      │          │  │  │           │
   ┌──┴──┐   ┌──┴──┐ ┌┴───┐  ┌────┴────┐
   │MCB  │   │MCB  │ │MCB │  │  MCB    │
   │6A   │   │16A  │ │20A │  │  32A    │
   └──┬──┘   └──┬──┘ └─┬──┘  └────┬────┘
      │         │      │          │
   ┌──┴──┐  ┌───┴──┐ ┌─┴───┐  ┌───┴────┐
   │Light│  │Socket│ │Geyser│ │  AC /   │
   │Points│ │Points│ │Point │ │  Heater │
   └─────┘  └──────┘ └──────┘ └────────┘

Protection Scheme (Components)

Key Points

1. Supply: 230 V, 50 Hz single-phase from NEA distribution pole via service wire.
2. Energy Meter: Records energy consumption in kWh.
3. Main Board: Houses the main switch, RCCB, and sub-circuit MCBs.
4. RCCB (30 mA): Trips within milliseconds when leakage current exceeds 30 mA, preventing fatal shocks.
5. Sub-circuit MCBs: Separate MCBs for lighting (6A), power sockets (16A), geyser (20A), and AC (32A) to isolate faults locally.
6. Earthing: All metal bodies of appliances and the earth bus bar are connected to the earth electrode (pipe/plate earthing) to safely divert fault current.
7. Colour Code: Phase – Red/Brown, Neutral – Black/Blue, Earth – Green/Yellow.

Runway Lights and Taxiway Lights in Airports

Runway Lights

1. Runway Edge Lights White lights along both edges of the runway, defining its lateral limits. They appear white from the landing direction and yellow from the opposite direction. High-intensity type is used for precision instrument runways.

2. Runway Threshold Lights Green lights at the beginning (threshold) of the runway, marking the start of the usable landing area. They are unidirectional and face the approaching aircraft.

3. Runway End Lights Red lights at the far end of the runway, marking the end of the usable runway surface. They face the landing direction and indicate "stop — no landing beyond this point."

4. Runway Centreline Lights White lights embedded along the centreline. Over the last 900 m of the runway they change to alternating red and white, and over the final 300 m they become all red — warning the pilot of the approaching runway end.

5. Touchdown Zone Lights White bar lights arranged in pairs on either side of the centreline in the touchdown zone, helping the pilot judge the touchdown point during landing.

6. Approach Lights A system of lights extending up to 900 m before the threshold (e.g., CALVERT system), showing white, then red, and finally green near the threshold, guiding the aircraft to align with the runway.

7. Runway Edge Light Variations

• Low Intensity Runway Lights (LIRL) — for non-instrument runways.
• Medium Intensity Runway Lights (MIRL) — for basic instrument runways.
• High Intensity Runway Lights (HIRL) — for precision approach runways.

Taxiway Lights

1. Taxiway Edge Lights Blue lights along both edges of the taxiway, defining its limits for ground movement at night or in low visibility.

2. Taxiway Centreline Lights Green lights embedded along the taxiway centreline, guiding the aircraft from the runway to the apron and vice versa. They are essential in low-visibility operations.

3. Stop Bars Red lights across the taxiway at the holding position before entering a runway. They indicate that the aircraft must stop and must not cross until clearance is given.

4. Runway Guard Lights (Holding Position Lights) Alternating yellow flashing lights (or yellow unidirectional lights) at the runway holding position, warning pilots and vehicle drivers that they are about to enter an active runway.

5. Clearance Bar Lights Yellow lights across the taxiway at intermediate holding positions (e.g., at intersections), indicating the position where clearance is required.

6. Taxiway Guidance Signs (Lighted) Illuminated signs with yellow/black or red/white markings that give directions, runway designations, and holding position information.

Summary Table

These lights together ensure safe aircraft movement during take-off, landing, and taxiing, especially at night and in poor visibility.

Importances of Earthing

Earthing (also called grounding) is the connection of the non-current-carrying metallic parts of an electrical installation to the general mass of earth through a low-resistance path. Its importances are:

1. Safety of human life: If a live conductor accidentally touches the metal body of a machine or appliance, the body becomes live. Earthing provides a low-resistance path, so the leakage current flows to earth and the fuse or MCB operates quickly, protecting the person from electric shock.
2. Protection of equipment: It carries away leakage currents and lightning/surge currents to earth, preventing damage to costly machines, transformers and appliances.
3. Voltage stabilization: It keeps the potential of the neutral point and metal bodies at or near earth potential, so that no dangerous voltage appears between the body and earth.
4. Proper operation of protective devices: A low earth resistance ensures a large fault current, which makes fuses, MCBs and earth-leakage circuit breakers (ELCB) operate reliably and instantly.
5. Protection from lightning: Earthing of towers, masts and lightning arrestors safely discharges lightning strokes into the earth.
6. Safety against static charge and fire: It drains static electricity and stray currents, reducing the risk of sparking and fire in inflammable areas.
7. Stability of power system: It provides a reference potential for the system and helps in the proper working of relays and instruments.

Types of Earthing

1. Pipe earthing A galvanized iron (GI) pipe of 38 mm to 50 mm diameter and about 2 to 3 m length is buried vertically in the ground, its lower portion perforated. A funnel with a wire mesh is fixed at the top for pouring water (in dry seasons) to keep the soil moist. The earth wire is bolted to the pipe. It is cheap, simple and commonly used for domestic and small installations. Depth depends on soil moisture; in dry soil a longer pipe is used.

2. Plate earthing A copper plate (60 cm × 60 cm × 3 mm) or GI plate (60 cm × 60 cm × 6 mm) is buried vertically in a pit about 3 m deep. The pit is filled in layers with salt and charcoal to reduce earth resistance. The earth wire is bolted to the plate. It gives low resistance and is used where a large fault current is expected, but it needs more space and labour.

3. Rod earthing A copper or GI rod of about 12.5 to 25 mm diameter is driven vertically into the ground by hammering, up to a depth of 3 m or more. No excavation or salt/charcoal is needed. It is cheap and quick, but the resistance is higher and it is suitable only where the soil is soft and moist.

4. Strip or wire earthing A copper strip (25 mm × 1.6 mm) or GI strip (25 mm × 4 mm) is buried horizontally in a trench about 0.5 m deep and 1 m long, or laid in a ring around the building. It is used where a number of earth connections are required and where a vertical electrode cannot be driven.

5. Water-main earthing The installation is connected to the underground metallic water pipe. It gives very low resistance, but it is not reliable because the pipe may be removed or joints may be made of insulating material. It is used only as a supplementary earth.

6. Chemical earthing A copper or GI electrode is placed in a pit filled with a chemical compound (bentonite, graphite, salt mixture) that retains moisture and keeps the resistance low and constant throughout the year. It is maintenance-free and used in rocky or dry soil and in substations.

7. Earthing through a mat (mesh earthing) A grid or mat of copper or GI strips is buried horizontally below a substation and connected to all equipment. It gives a very low resistance and equalizes the potential over the whole area, protecting both men and equipment in high-voltage substations.

Factors that Determine Cable Size for Electrical Wiring

The size of a cable (its cross-sectional area in mm²) is decided so that it can carry the load current safely without excessive voltage drop, overheating or mechanical failure. The main determining factors are:

1. Load current (current-carrying capacity) The full-load current of the circuit is calculated first. The cable must have a current rating equal to or greater than this current. For a three-phase load, $I = \frac{P}{\sqrt{3}\,V\cos\phi}$ and for a single-phase load, $I = \dfrac{P}{V\cos\phi}$.

2. Permissible voltage drop Voltage drop from the supply point to the farthest load must be within the limit (generally 2.5% for lighting and 5% for power circuits as per NEA practice). Longer runs and higher currents cause greater drop, so a larger size is required. For a single-phase circuit, $V_d = \frac{2\,L\,I\,\rho}{A}$ where $L$ = length (m), $I$ = current (A), $\rho$ = resistivity of conductor, $A$ = area (mm²).

3. Length of the circuit / cable run The longer the cable, the higher the resistance and voltage drop; hence longer runs need bigger cables.

4. Type of load and supply system Resistive or inductive load, power factor, single-phase or three-phase supply, and starting current of motors all affect the required size. Motor circuits need a larger size to withstand starting current.

5. Type of insulation PVC (70 °C), XLPE (90 °C) or rubber insulation have different temperature ratings. Higher temperature rating allows a smaller cable for the same current.

6. Ambient temperature Cables in hot locations (boiler rooms, roofs) must be derated using a temperature correction factor, so a larger size may be needed.

7. Method of installation and grouping Cables in conduit, buried underground, in trays or in air dissipate heat differently. When several cables are bunched together, a grouping (derating) factor is applied, requiring a larger size.

8. Number of conductors and cores Single-core, two-core, three-core or four-core cables have different current ratings for the same area.

9. Short-circuit / fault current withstand The cable must withstand the prospective short-circuit current for the time taken by the protective device to operate, without damage to insulation.

10. Coordination with protective device The cable rating must be coordinated with the rating of the fuse or MCB so that the protective device operates before the cable is overloaded.

11. Mechanical strength and minimum size A minimum size is fixed for mechanical strength (e.g. 1.5 mm² for lighting, 2.5 mm² for power circuits) so that the cable is not damaged during installation.

12. Future expansion and diversity factor Provision for future additional load and the diversity factor of the installation influence the selected size.

13. Environment and cost Moisture, corrosive atmosphere, underground or overhead laying, and economy of the installation also guide the final choice.

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Standard Cable Sizes (mm²) Used in Wiring

Standard conductor cross-sectional areas manufactured and used in Nepal (as per NS/IEC) are:

$0.5,\ 0.75,\ 1,\ 1.5,\ 2.5,\ 4,\ 6,\ 10,\ 16,\ 25,\ 35,\ 50,\ 70,\ 95,\ 120,\ 150,\ 185,\ 240,\ 300,\ 400,\ 500,\ 630\ \text{mm}^2$

Residential wiring

Commercial wiring (shops, offices, hotels)

Industrial wiring

Note: For final sub-circuits the minimum size is 1.5 mm² for lighting and 2.5 mm² for power circuits; for motor circuits the size is selected from the above standard list after applying voltage-drop and derating factors.

Objectives of community health diagnosis

1. To identify the health problems and health needs of a defined community.
2. To find out the causes and risk factors behind those problems (biological, environmental, social, economic, cultural).
3. To assess the existing health resources, services and facilities available in the community.
4. To determine the health priorities of the community so that planning can be need-based.
5. To create awareness and participation among community people about their own health.
6. To provide a factual basis for planning, implementing and evaluating health programmes.
7. To help in the proper allocation of limited health budget and manpower.

Scope of community health diagnosis

1. Geographical scope — covers a clearly defined area such as a ward, VDC/municipality or a specified catchment area of a health institution.
2. Population scope — includes all age groups, both sexes, and special groups like mothers, children, elderly, disabled and marginalized people.
3. Health status — morbidity, mortality, nutritional status, immunization status, maternal and child health, communicable and non-communicable diseases.
4. Environmental aspect — drinking water, sanitation, housing, waste disposal, air and vector conditions.
5. Socio-economic aspect — education, occupation, income, food habits, beliefs and customs affecting health.
6. Health services aspect — availability, accessibility, utilization and quality of curative, preventive and promotive services.
7. Resource aspect — health manpower, budget, equipment, drugs, and support from local bodies, NGOs and FCHVs.
8. Time scope — it is a continuous process, repeated periodically to update the community health profile.

Epidemiological Triad (Agent–Host–Environment Model)

The epidemiological triad is the classic model used to explain the occurrence and spread of a disease. It states that a disease results from the interaction of three factors: agent, host, and environment. When these three are in balance, health is maintained; when the balance is disturbed, disease occurs. It is also called the triangle of disease causation and is most useful for communicable (infectious) diseases.

1. Agent The agent is the factor whose presence, excessive presence, or absence is necessary for the disease to occur. It may be:

• Biological — bacteria, viruses, protozoa, fungi, helminths (e.g., Mycobacterium tuberculosis).
• Nutritive — deficiency or excess of nutrients (e.g., iron deficiency anaemia).
• Physical — heat, cold, radiation, mechanical injury.
• Chemical — pesticides, drugs, poisons, allergens.

The agent is described by its infectivity, pathogenicity, virulence, and dose.

2. Host The host is the person (or animal) in which the disease occurs. The host's susceptibility or resistance depends on:

• Age, sex, race, and genetic constitution
• Immunity (natural or acquired)
• Nutritional status
• Occupation, lifestyle, and behaviour (e.g., smoking, unsafe sex)
• Psychological state and stress

3. Environment The environment includes all external factors that influence the agent and the host, and the way they interact:

• Physical — air, water, soil, climate, housing, sanitation
• Biological — vectors, reservoirs, animal hosts, plants
• Social and economic — income, education, occupation, culture, health services, crowding

Interaction of the three Disease occurs when the agent is able to leave its reservoir, reach a susceptible host, and enter in sufficient dose, in an environment that favours transmission. For example, in tuberculosis: the agent is M. tuberculosis, the host is a malnourished, unimmunised person living in a crowded room, and the environment is a poorly ventilated, overcrowded house with low income and poor access to health care. If any one arm of the triangle is broken — by immunisation (host), chemotherapy or disinfection (agent), or improved ventilation and nutrition (environment) — the disease can be prevented or controlled.

Conclusion The epidemiological triad explains that disease is not caused by a single factor but by the interaction of agent, host, and environment. Therefore, prevention and control measures must be directed at all three components, not at the agent alone.

First aid steps in the management of a near-drowning patient

Near drowning is a condition in which a person survives, at least temporarily, after suffocation by submersion in water. The main problem is lack of oxygen (hypoxia) and fluid in the lungs. The aim of first aid is to restore breathing and circulation as early as possible and to prevent further complications.

Steps:

1. Ensure safety of the rescuer first. Do not jump into the water unless trained. Use a rope, pole, boat or float to reach the victim. Remove the victim from the water carefully, keeping the head and neck in line to avoid spinal injury (especially after diving).

2. Check responsiveness and breathing. Call the victim's name and tap the shoulders. Look, listen and feel for breathing for not more than 10 seconds. If the victim is not breathing, start resuscitation immediately.

3. Open the airway. Place the victim on a hard flat surface. Tilt the head back and lift the chin (head-tilt chin-lift). If spinal injury is suspected, use the jaw-thrust method instead. Remove any visible mud, weed, sand or denture from the mouth with fingers or a cloth.

4. Give rescue breaths / CPR. If the victim is not breathing but has a pulse, give artificial respiration (mouth-to-mouth) — 2 initial breaths, then about 10–12 breaths per minute. If there is no pulse and no breathing, start cardiopulmonary resuscitation (CPR): 30 chest compressions followed by 2 rescue breaths, and continue until help arrives. Chest compressions should be at least 100–120 per minute.

5. Do NOT try to drain water from the lungs. Do not press the abdomen, hold the victim upside down or waste time on this. Only clear the mouth and start breathing support. (Abdominal thrusts may be used only if there is a solid obstruction in the airway.)

6. Place in recovery position. If breathing returns but the victim is unconscious, turn him/her to the recovery position (lying on the side) so that vomit or water can drain out and the tongue does not block the airway.

7. Keep the victim warm. Remove wet clothes, cover with a blanket or dry cloth, and keep the body warm to prevent hypothermia.

8. Do not give food or drink. Nothing should be given by mouth until the patient is fully conscious and medical advice is obtained.

9. Shift to hospital immediately. Even if the victim appears to recover, take him/her to the nearest health facility, because complications such as pneumonia, pulmonary oedema, electrolyte imbalance and delayed breathing difficulty may develop later. Inform the doctor about the time and duration of submersion.

Key points to remember: Early rescue breathing is the most important step; CPR should be started without delay; never waste time draining water; and all near-drowning victims must be medically evaluated even if they seem normal.

Why Hospital Waste Disposal is Sensitive

Hospital waste (health care waste) is sensitive for the following reasons:

1. Infectious nature — It contains pathogens (bacteria, viruses, fungi) from blood, body fluids, used syringes, dressings and human tissue, so it can spread diseases like HIV/AIDS, hepatitis B and C, tetanus and tuberculosis to patients, health workers, waste handlers and the general public.
2. Sharps and injuries — Needles, blades, broken glass and ampoules cause needle-stick injuries, which are the main route of infection transmission.
3. Toxic and hazardous chemicals — Expired medicines, cytotoxic (cancer) drugs, mercury, and laboratory reagents are poisonous and can contaminate soil and water.
4. Radioactive waste — Waste from radiotherapy and imaging units emits radiation and needs special handling and decay storage.
5. Environmental pollution — If mixed with ordinary municipal waste and burned in the open or dumped in rivers, it releases toxic gases (dioxins, furans) and pollutes air, water and soil.
6. Risk of reuse and recycling — Syringes, IV sets and gloves may be washed and resold as scrap, spreading infection in the community.
7. Legal and ethical obligation — National and international rules (e.g., WHO guidelines, Nepal's Solid Waste Management Act) require safe segregation, storage, transport and final disposal, with penalties for violation.
8. Public fear and social impact — Improper disposal near settlements creates panic, bad smell, flies, rodents and loss of public trust in health institutions.

Because of these high health, environmental and legal risks, hospital waste disposal is treated as a sensitive task requiring colour-coded segregation at source, trained staff, protective equipment and safe final disposal.

Methods of Solid Waste Disposal

1. Landfilling (Sanitary landfill) — Waste is spread in layers in a low-lying pit, compacted and covered daily with soil; leachate and landfill gas are collected. Simple and cheap, but needs land and careful site selection.
2. Incineration — Burning waste at high temperature (800–1000°C) in a closed chamber, reducing it to ash. Suitable for infectious and sharps waste, but costly and causes air pollution if not controlled.
3. Composting — Biodegradable organic waste is decomposed by microorganisms into manure. Useful for kitchen and garden waste; needs segregation and moisture control.
4. Vermicomposting — Earthworms convert organic waste into nutrient-rich vermicompost; eco-friendly and low cost.
5. Recycling — Paper, plastic, glass and metal are collected, processed and made into new products; saves raw material and energy.
6. Reuse — Containers, bottles and other items are cleaned and used again; reduces waste volume at source.
7. Open dumping — Waste is thrown in open pits or roadsides. It is the commonest but unhygienic method, causing flies, odour and disease; not recommended.
8. Open burning — Burning waste in the open air; easy but causes serious air pollution and is banned for hospital waste.
9. Autoclaving / Microwave / Chemical disinfection — Non-burn treatment methods that sterilise infectious waste before final disposal (mainly for hospital waste).
10. Anaerobic digestion (Biogas plant) — Organic waste is digested in the absence of air to produce biogas and slurry; good for wet biodegradable waste.
11. Feeding to animals — Food waste is used as animal feed after proper treatment.
12. Ocean/river dumping — Waste is dumped into water bodies; harmful to aquatic life and now discouraged or banned.

First aid management of suspected organophosphorus (OP) poisoning

1. Ensure scene safety and personal protection. OP compounds are absorbed through skin and by inhalation. Put on gloves (and mask/apron if available), move the patient to fresh air, and avoid direct contact with vomit, secretions or contaminated clothing.

2. Remove contaminated clothing and decontaminate the skin. Strip off all contaminated clothes and double-bag them. Wash the skin thoroughly with soap and plenty of running water for at least 10–15 minutes. Flush the eyes with clean water if exposed. Do not use hot water or rub the skin, as this increases absorption.

3. Assess and secure the airway, breathing and circulation (ABC). Check responsiveness and pulse. OP poisoning causes excessive secretions, bronchospasm and respiratory muscle paralysis, so:

   • Clear the mouth and throat of secretions/vomit.
   • Place the patient in the recovery (left lateral) position if unconscious but breathing, to prevent aspiration.
   • Give supplemental oxygen if available.
   • Be ready to assist ventilation with a bag-valve-mask if breathing is inadequate. Avoid mouth-to-mouth ventilation, as the rescuer may be poisoned by the patient's exhaled toxins.

4. Identify and limit further absorption. If poisoning is by ingestion within about an hour and the patient is fully conscious, do not induce vomiting (kerosene-like solvents in the formulation may cause aspiration pneumonia). Do not give milk, oil or any home remedy. Never give anything by mouth to an unconscious patient. Gastric lavage and activated charcoal are hospital procedures, not first-aid measures.

5. Call for emergency help and arrange rapid transport. Contact the nearest ambulance/emergency number or health facility immediately. Inform them that OP poisoning is suspected so that atropine and pralidoxime can be kept ready. Carry the pesticide container, label or a sample of the vomit to help identify the poison.

6. Monitor and keep the patient warm. Continuously watch breathing, pulse and level of consciousness. Record the time of exposure, amount and route, and the time first aid was started. Reassure the patient and keep him/her warm until the ambulance arrives.

Ways by which mothers and other family members can prevent diarrhoea among children

Diarrhoea in children is mostly caused by contaminated water, food, dirty hands and poor sanitation. It can be prevented by the following measures:

1. Safe drinking water: Boil water before drinking, or use a filter or chlorine tablets. Store drinking water in a clean, covered pot and use a clean glass or jug to take it out, so that hands do not touch the water.

2. Hand washing: Wash hands with soap and clean water before preparing or eating food, after using the toilet, after cleaning a child's stool, and after handling garbage. This is the single most effective measure.

3. Food hygiene: Give children freshly cooked food. Keep food covered and protect it from flies. Wash fruits and vegetables with clean water before eating. Do not give stale, uncovered or street food kept in the open.

4. Safe disposal of stool: Use a toilet and teach children to use it. Dispose of children's stool in the toilet, not in the open. This stops germs from reaching water and food sources.

5. Exclusive breastfeeding: Breastfeed infants for the first six months only. Breast milk is clean and gives protection against diarrhoea. Continue breastfeeding up to two years along with other food.

6. Immunization: Get children vaccinated, especially against rotavirus and measles, as these diseases cause severe diarrhoea.

7. Clean surroundings: Keep the house, kitchen and yard clean. Cover water sources. Manage garbage properly and keep flies away.

8. Care during diarrhoea: If diarrhoea occurs, give ORS (Oral Rehydration Solution) and zinc tablets, continue feeding, and take the child to a health worker if it is severe or does not stop.

Conclusion: Mothers and family members can greatly reduce diarrhoea among children by safe water, hand washing, clean food, proper toilet use, breastfeeding and immunization.

Importance of Breastfeeding

1. Importance for Infant Nutrition and Development

Nutritional importance:

• Complete food: Breast milk provides all the nutrients — carbohydrates (lactose), proteins (casein, whey), fats, vitamins, minerals and water — in the right proportion needed by an infant for the first 6 months. No extra water or food is required.
• Easily digestible: Its proteins and fats are easily digested and absorbed by the immature digestive system of the newborn.
• Balanced composition: The composition changes according to the growing need of the baby (colostrum in the first days, transitional milk, then mature milk).
• Colostrum (first milk): Thick, yellowish milk rich in protein, vitamin A, zinc and antibodies (IgA). It acts as the baby's "first immunisation" and also has a laxative effect that helps clear meconium.

Developmental importance:

• Brain development: Long-chain polyunsaturated fatty acids (DHA, AA) and lactose promote rapid brain and nervous system development, giving higher IQ and better learning ability.
• Physical growth: Balanced protein, calcium and phosphorus support healthy bone and muscle growth.
• Emotional and social development: Skin-to-skin contact, warmth and the mother's heartbeat give the baby a sense of security, trust and emotional bonding (attachment), which builds a healthy personality.
• Jaw and dental development: Suckling exercises the jaw and helps proper alignment of teeth and speech development.
• Protection from disease: Immunoglobulins, lactoferrin, lysozyme and white blood cells protect the baby from diarrhoea, pneumonia, ear infection, allergy, asthma and malnutrition. It also reduces the risk of obesity and diabetes in later life.

2. Importance for the Health of Mothers

• Prevents postpartum haemorrhage: Suckling releases oxytocin, which contracts the uterus and reduces bleeding after delivery.
• Helps the uterus return to normal size (involution) quickly.
• Family planning (birth spacing): Exclusive breastfeeding causes lactational amenorrhoea (absence of menstruation) for about 6 months, which acts as a natural contraceptive (LAM) and helps space births.
• Reduces risk of cancer: Lower risk of breast cancer, ovarian cancer and endometrial cancer.
• Reduces anaemia and helps weight loss: Menstruation is delayed, so iron is saved; the extra fat stored during pregnancy is used up, helping the mother return to her pre-pregnancy weight.
• Reduces risk of type 2 diabetes, hypertension, heart disease and osteoporosis in later life.
• Saves money and time: No need to buy formula milk, bottles, fuel for sterilisation; the milk is always fresh, clean and at the right temperature.
• Psychological benefit: Gives the mother confidence, satisfaction and emotional closeness with the baby; reduces the risk of postpartum depression.

3. Benefits of Exclusive Breastfeeding to the Lactating Mother

Exclusive breastfeeding means giving only breast milk (no water, no other food, no bottle) for the first 6 months.

• Natural contraception: Frequent suckling keeps prolactin high and suppresses ovulation, giving about 98% protection from pregnancy in the first 6 months (Lactational Amenorrhoea Method).
• Faster recovery: Uterus contracts faster, lochia stops earlier, and the mother regains strength sooner.
• Less blood loss and less anaemia: Delayed menstruation conserves iron stores.
• Weight reduction: About 500 kcal is used daily for milk production, so extra pregnancy weight is lost gradually without dieting.
• Lower risk of breast and ovarian cancer because of reduced lifetime ovulatory cycles and hormonal changes.
• Better emotional health: Less stress, better sleep pattern (with night feeding), stronger mother–baby bond, less postpartum depression.
• Economic benefit: Saves the cost of formula milk, bottles and health care for sick babies; less absence from work.
• Convenience: No preparation, no sterilisation, always available, and can be given anywhere, day or night.
• Better health of the mother in later life: Lower risk of diabetes, hypertension, high cholesterol and heart disease.

Conclusion: Breastfeeding is the safest, cheapest and most complete way of feeding an infant. It protects both the child and the mother, so it should be started within one hour of birth, given exclusively for 6 months, and continued with complementary food up to 2 years or more.

Clinical Features and Risk Factors of Filariasis

Clinical Features

Filariasis (lymphatic filariasis) is caused by Wuchereria bancrofti, Brugia malayi and Brugia timori, transmitted by Culex, Anopheles and Aedes mosquitoes. Most infections are asymptomatic; clinical disease appears after years of repeated exposure.

Acute features:

• Filarial fever with lymphangitis and lymphadenitis (retrograde spread along the lymphatics)
• Painful, tender, red-streaked swelling of the affected limb or scrotum
• Acute funiculitis, epididymitis and orchitis in males
• Transient lymphoedema that resolves after the acute attack

Chronic features:

• Lymphoedema of the limb (usually leg), progressing to elephantiasis with thickened, rough, verrucous skin
• Hydrocele — the commonest chronic manifestation in males
• Chyluria (milky urine) due to rupture of lymphatics into the urinary tract
• Lymph scrotum, vulval lymphoedema in females
• Tropical pulmonary eosinophilia (TPE) — nocturnal cough, wheezing, breathlessness, eosinophilia
• Secondary bacterial and fungal infection of the lymphoedematous limb (acute dermatolymphangioadenitis — ADLA)

Risk Factors

• Residence in or travel to endemic areas (Terai districts of Nepal)
• Repeated mosquito bites; sleeping without a mosquito net
• Poor environmental sanitation, stagnant water and poor drainage near the house
• Low socio-economic status, poor hygiene and bare feet
• Male sex (hydrocele, funiculitis) and adults in the productive age group
• Untreated or repeated infection and lack of mass drug administration coverage

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National Objectives, Prevention and Control Strategies and Current Activities for Malaria Control

National Objectives

1. To reduce malaria morbidity and mortality and eventually eliminate malaria from Nepal.
2. To interrupt local transmission of malaria by Plasmodium falciparum and P. vivax.
3. To achieve malaria-free status (zero indigenous cases) by 2026 and certification of elimination by 2030.
4. To strengthen surveillance, early diagnosis and prompt treatment in all health facilities.
5. To prevent re-establishment of transmission in malaria-free areas.

Prevention and Control Strategies

Vector control:

• Indoor residual spraying (IRS) with insecticides in high-risk areas
• Distribution and promotion of long-lasting insecticidal nets (LLINs)
• Environmental management — filling ditches, clearing stagnant water, drainage

Case management:

• Early diagnosis by rapid diagnostic test (RDT) and microscopy
• Prompt treatment with ACT (artemisinin-based combination therapy) for P. falciparum and primaquine for P. vivax
• Free diagnosis and treatment at government health facilities

Surveillance:

• Case detection, reporting and investigation; active case search in outbreak areas
• Malaria elimination surveillance in low-transmission districts

Intersectoral and community measures:

• Health education on net use, early treatment and personal protection
• Coordination with local government, NGOs and community health volunteers (FCHVs)
• Epidemic preparedness and rapid response teams

Current Activities to Control Malaria

• Implementation of the National Malaria Strategic Plan (2016–2025) with elimination as the goal
• Distribution of LLINs and IRS in endemic districts (Terai and inner Terai)
• Free RDT and microscopy services at health posts, and treatment through FCHVs
• Malaria case-based surveillance and elimination registers in low-endemic districts
• Screening of migrant and mobile populations and cross-border collaboration with India
• Vector surveillance and outbreak investigation in high-risk districts
• Health education campaigns and observance of Malaria Day
• Monitoring and supervision by the Epidemiology and Disease Control Division (EDCD)

Steps of measurement of blood pressure

1. Preparation of the patient: Make the patient sit comfortably, rest for at least 5 minutes, keep the arm bare and supported at heart level, and ensure the patient has not taken coffee, smoked, or exercised in the last 30 minutes.

2. Preparation of the instrument: Check that the sphygmomanometer and stethoscope are in working order. Select a cuff of proper size (bladder should cover about 80% of the arm circumference and two-thirds of the arm length).

3. Positioning the cuff: Wrap the cuff snugly around the upper arm, 2–3 cm above the antecubital fossa (elbow crease), with the centre of the bladder over the brachial artery. The lower edge of the cuff should be at the level of the heart.

4. Locating the artery: Palpate the brachial artery at the antecubital fossa and place the stethoscope bell (or diaphragm) over it without touching the cuff.

5. Estimating systolic pressure (palpatory method): Inflate the cuff while palpating the radial pulse until the pulse disappears, then note the reading; this gives an approximate systolic value and prevents over-inflation.

6. Inflation: Close the valve and inflate the cuff to about 20–30 mmHg above the estimated systolic pressure.

7. Deflation and auscultation: Place the stethoscope over the brachial artery, open the valve slowly so that the pressure falls at 2–3 mmHg per second, and listen for the Korotkoff sounds:

   • Phase I (first clear tapping sound) = systolic pressure
   • Phase II (murmuring)
   • Phase III (crisper sound)
   • Phase IV (muffling)
   • Phase V (sound disappears) = diastolic pressure

8. Recording: Note the systolic and diastolic readings (e.g. 120/80 mmHg), record the arm used and the position of the patient.

9. Repeat and average: Wait 1–2 minutes and take a second reading; average the two readings for accuracy.

Services provided by Female Community Health Volunteers (FCHVs) — 5 marks

Female Community Health Volunteers (FCHVs) are local women (generally 25–45 years old, literate, and selected by the community) trained by the Government of Nepal to act as a bridge between the community and the formal health system. The main services they provide are:

1. Maternal and newborn care

• Identify pregnant women and counsel them on antenatal check-ups (at least 4 visits), danger signs, and institutional delivery.
• Distribute iron/folate tablets and encourage rest and adequate nutrition.
• Promote birth preparedness, refer mothers for delivery, and follow up mother and newborn after birth (postnatal care).
• Counsel on family planning and distribute condoms, oral pills, and emergency contraceptive pills.

2. Child health services

• Treat childhood diarrhoea with ORS and zinc; distribute ORS packets and zinc tablets.
• Treat pneumonia in children with cotrimoxazole (as per protocol) and refer severe cases.
• Promote immunisation and assist health workers during immunisation campaigns.
• Counsel on breastfeeding, complementary feeding, and growth monitoring.

3. Nutrition services

• Screen children under 5 for malnutrition using MUAC tape and refer severe cases.
• Distribute Vitamin A capsules and deworming tablets during campaigns.
• Counsel on maternal nutrition and micronutrient supplementation.

4. Disease prevention and control

• Distribute insecticide-treated bed nets and give health education on malaria, dengue, TB, and HIV/AIDS.
• Support DOTS treatment for TB patients and follow up defaulters.
• Conduct health education on sanitation, safe drinking water, and hygiene.

5. Health promotion and referral

• Provide first aid and basic medicines from the FCHV medicine kit.
• Identify and refer serious cases to health posts, PHCCs, or hospitals.
• Conduct home visits, mothers' group meetings, and community awareness programmes.
• Support national campaigns (polio, measles, vitamin A, deworming) and record/report data to the health facility.

Conclusion: FCHVs act as the first contact point for health care in rural Nepal, improving maternal, child, and community health through counselling, basic treatment, and referral services.

Transmission of measles infection

Measles is a highly contagious viral disease caused by the measles virus (a paramyxovirus). It is transmitted from person to person mainly by:

1. Airborne route — inhalation of virus-containing droplets or droplet nuclei (aerosols) that remain suspended in the air for up to about two hours after an infected person has coughed or sneezed.
2. Droplet route — direct contact with large respiratory droplets expelled by an infected person during coughing, sneezing, talking or breathing.
3. Direct/indirect contact — contact with nasal or throat secretions of an infected person, or with articles freshly soiled by such secretions.

The patient is infectious from about 4 days before the appearance of the rash to about 4 days after it appears. The virus enters the body through the respiratory tract or conjunctiva. There is no carrier state and no animal reservoir — humans are the only host.

Diagnosis of a suspected case of measles

Diagnosis is made on the basis of clinical features supported by laboratory tests:

Clinical diagnosis

1. History — fever with cough, coryza (running nose) and conjunctivitis (the "three C's"), and a typical rash appearing 3–4 days after fever; history of contact with a measles case; and immunization status.
2. Examination —
   • Koplik's spots: small greyish-white spots with a red base on the buccal mucosa opposite the second molars, appearing 1–2 days before the rash; they are pathognomonic of measles.
   • Rash: maculopapular, starting behind the ears and on the face, spreading downwards to the trunk and limbs; it fades in the same order, leaving brownish staining and fine desquamation.
   • Fever and general signs of toxicity; look for complications such as pneumonia, otitis media, diarrhoea and encephalitis.

Laboratory confirmation

2. Serology — detection of measles-specific IgM antibody in serum (best taken 4–28 days after rash onset) is the standard test.
3. Virus detection — RT-PCR of throat swab, nasal swab or urine to detect viral RNA, and virus isolation in cell culture.
4. Other supportive tests — complete blood count (leucopenia), chest X-ray if pneumonia is suspected.

A suspected case is confirmed when there is fever with rash plus cough, coryza or conjunctivitis, together with either laboratory confirmation or an epidemiological link to a confirmed case.

Management of a patient with suspected acute appendicitis

1. Assessment and resuscitation

• Take history: migratory right iliac fossa pain, anorexia, nausea/vomiting, low-grade fever.
• Examine: vital signs, tenderness and guarding at McBurney's point, Rovsing's, Blumberg's and psoas signs.
• Keep nil per os, secure IV access, start IV fluids, give analgesia and antiemetic, correct dehydration and electrolytes.

2. Investigations

• CBC (leucocytosis with neutrophilia), CRP, urine routine/microscopy (to exclude UTI), serum β-hCG in women of childbearing age.
• Ultrasound abdomen/pelvis; CT scan if diagnosis is doubtful or in obese/elderly patients.
• Appendicitis inflammatory response (AIR) or Alvarado score to support the diagnosis.

3. Pre-operative preparation

• Confirm diagnosis and consent; keep patient fasting.
• Start broad-spectrum IV antibiotics (e.g., ceftriaxone + metronidazole).
• Arrange blood grouping, cross-matching and anaesthetic fitness.

4. Definitive treatment

• Appendicectomy — laparoscopic (preferred) or open — is the treatment of choice.
• If an appendicular mass (appendix mass) is present: conservative management with IV antibiotics and fluids, followed by interval appendicectomy after 6–8 weeks.
• If an abscess is present: ultrasound-guided drainage plus antibiotics.

5. Post-operative care

• Continue IV antibiotics and fluids, then oral feeds as bowel sounds return.
• Adequate analgesia, early ambulation, wound care and watch for complications (wound infection, paralytic ileus, abscess, faecal fistula).
• Discharge with advice and follow-up; histopathology of the specimen to confirm the diagnosis.

Difference between Gram-positive and Gram-negative bacteria

Key point: The difference lies in the thickness of the peptidoglycan layer and the presence of the outer membrane, which together decide whether the bacterium retains the primary stain or not.

Supervision and Monitoring in the Municipal Health System

Supervision and monitoring are two distinct but complementary management functions used in the municipal (local level) health system to ensure that health services are delivered efficiently, effectively and as per the standards set by the federal and provincial governments.

1. Supervision

Supervision is a supportive, continuous and face-to-face process in which a senior health official guides, advises, and builds the capacity of subordinate health workers to improve their performance. It is mainly corrective and educational in nature.

In the municipal health system, supervision is carried out at the following levels:

• Municipal Health Section / Health Coordinator supervises the Health Post In-charge, ANMs, AHWs, and community-level health workers.
• Health Post In-charge supervises Female Community Health Volunteers (FCHVs) and other field-level staff.
• Provincial and Federal level (Health Office, Ministry of Health) provide technical supervision to the municipality.

Key aspects of supervision:

• On-site visit and observation of work
• Review of records, reports and registers
• Identification of problems and provision of on-the-spot coaching
• Supportive feedback and motivation of staff
• Ensuring availability of medicines, equipment and supplies

2. Monitoring

Monitoring is a continuous and systematic process of collecting, reviewing and using information to track whether health programmes and activities are progressing as planned. It is mainly informative and preventive in nature.

In the municipal health system, monitoring is done through:

• Regular reporting from Health Posts, Birthing Centres and FCHVs (e.g., monthly/quarterly reports to HMIS)
• HMIS (Health Management Information System) data and its analysis
• Field visits by municipal health officials
• Review meetings at ward and municipal level
• Community feedback and social audit

Key aspects of monitoring:

• Tracking of indicators (immunization coverage, institutional delivery, ANC visits, etc.)
• Comparison of progress against targets
• Identification of gaps and timely corrective action
• Reporting to the municipal assembly and provincial/federal bodies

3. Legal and Institutional Basis

• The Constitution of Nepal (2072) lists health as a concurrent subject of federal, provincial and local levels.
• The Local Government Operation Act, 2074 assigns the municipality the responsibility of operating, supervising and monitoring basic health services.
• The Municipality Health Section and Health Post Management Committee are the main institutional mechanisms.

4. Difference between Supervision and Monitoring

Conclusion

In the municipal health system, supervision focuses on improving the performance of health workers, while monitoring focuses on tracking the progress of health programmes. Both are essential for quality health service delivery, and together they help the municipality achieve its health goals as per the federal structure of Nepal.

Steps in Outbreak Investigation of a Water-Borne Disease in a Rural Community

An outbreak investigation follows a systematic, stepwise approach. For a water-borne disease in a rural setting (e.g., diarrhoea, cholera, typhoid, hepatitis A), the steps are:

1. Verification of the Outbreak

• Confirm that the reported number of cases is genuinely above the expected level for that area and time.
• Compare with previous weeks'/years' surveillance data (baseline).
• Confirm the diagnosis clinically and, where possible, by laboratory testing of stool/water samples.

2. Confirmation of the Existence of an Outbreak

• Define an epidemic threshold and verify that cases exceed it.
• Rule out reporting artefacts, changes in diagnostic practice, or duplicate reporting.

3. Definition of a Case

• Establish a case definition (person, place, time, clinical features, laboratory criteria).
• Classify as suspected, probable, and confirmed cases.

4. Case Finding and Line Listing

• Actively search for cases (house-to-house survey, health facility records, community informants).
• Prepare a line list with name, age, sex, address, date of onset, symptoms, water source used, and outcome.

5. Descriptive Epidemiology (Time, Place, Person)

• Time: Draw an epidemic curve to determine the mode of spread and probable time of exposure.
• Place: Plot cases on a spot map to identify clustering around a particular water source.
• Person: Analyse by age, sex, occupation, and other characteristics to identify high-risk groups.

6. Generation of Hypothesis

• Form a hypothesis about the likely source (e.g., contaminated tube well, river, or piped supply) and mode of transmission (faecal–oral route).
• Consider environmental, behavioural, and infrastructural factors.

7. Analytical Epidemiology

• Conduct a case–control or retrospective cohort study.
• Calculate attack rates, odds ratio/relative risk, and test for statistical significance.
• Identify the specific water source or practice associated with illness.

8. Environmental and Laboratory Investigation

• Inspect water sources: distance from latrines, drainage, animal sheds, and possibility of leakage.
• Test water for faecal contamination (E. coli, coliform count) and for the specific pathogen.
• Assess chlorination, boiling, and storage practices.

9. Control and Prevention Measures

• Immediate: Boil/chlorinate drinking water, provide safe water supply, disinfect contaminated sources, isolate and treat cases, and use ORS for dehydration.
• Long-term: Protect water sources, improve sanitation and latrines, health education on hand washing and safe storage, and regular water quality monitoring.

10. Communication and Reporting

• Inform the local health authority, District Public Health Office, and community leaders.
• Report findings through the routine surveillance system (EWARS/HMIS).

11. Follow-up and Evaluation

• Monitor for new cases to confirm that control measures are effective.
• Document the investigation, lessons learned, and recommendations for future prevention.

Conclusion: A prompt, systematic investigation identifies the source of contamination, guides immediate control measures, and prevents further spread of the water-borne disease in the rural community.

Vaccines, Schedule and Doses under Nepal's National Immunization Programme

Nepal's National Immunization Programme (NIP), run under the Child Health Division of the Department of Health Services, follows the routine immunization schedule below. All routine vaccines are given free of cost.

1. Vaccines and Schedule

2. Key Points to Remember

• At birth: BCG, Hepatitis B birth dose (within 24 hours), and OPV-0 (within 15 days).
• At 6, 10 and 14 weeks: Pentavalent, OPV and PCV (Rotavirus at 6 and 10 weeks only); IPV is given at 14 weeks.
• At 9 months: First dose of MR.
• At 12 months: First dose of JE (endemic districts).
• At 15 months: Second dose of MR.
• At 24 months: Second dose of JE.
• At 10 years and 16 years: Td (Tetanus–Diphtheria) — two doses.
• Vitamin A is also given as a supplementary dose at 6 months and every 6 months thereafter up to 5 years, along with deworming (Albendazole) from 1 year onwards.

3. Note on Recent Changes

The schedule is periodically revised by the Child Health Division. Recent changes include replacement of the measles vaccine with MR, introduction of PCV and Rotavirus vaccines nationwide, and replacement of DPT with Pentavalent. Candidates should state the schedule currently in force as per the latest NIP guidelines.