Lesson 9: Disaster Management

In the figure : In the figure the focal point is where the earthquake starts inside the earth. The epicentre is the point on the surface just above it, so the waves reach it first and the loss is greatest there.

Rule 1: Focus and epicentre — Shocks and seismic waves formed inside the earth spread over the surface in all directions. The epicentre receives them first, so the major loss occurs near it. Farther away, the shaking is weaker.

• Easy : A village near the epicentre is shaken more than a town far away.
• Medium : Seismic waves travel in all directions, like ripples spreading when a stone falls in a pond.
• Exam-type : The point directly above the focus is the epicentre; this is where waves arrive first.

In the figure : In the figure a seismograph records the seismic waves as a wavy line. The intensity of an earthquake is measured on the Richter scale.

Rule 2: Seismograph and Richter scale — The instrument that records earthquakes is the seismograph (भूकंपमापी). The intensity is measured on the Richter scale (रिश्टर मापनश्रेणी). A higher reading means a stronger earthquake.

• Easy : A seismograph draws a wavy line when the ground shakes.
• Medium : A reading of 7 on the Richter scale is stronger than a reading of 4.
• Exam-type : Each step on the Richter scale means roughly ten times more ground motion, so 6 is about 10 × 10 = 100 times stronger movement than 4.

In the figure : In the figure mild earthquakes occur in larger numbers than intense ones (sample units shown). Nearly 12,400 to 14,000 earthquakes occur on the earth every year.

Rule 3: How often they occur — Mild earthquakes occur in larger numbers than intense ones. Nearly 12,400 to 14,000 earthquakes occur every year, so the earth is continuously vibrating.

• Easy : Most earthquakes are so mild that we do not feel them.
• Medium : 12,400 earthquakes a year are about 12,400 ÷ 365 = 34 each day.
• Exam-type : 14,000 − 12,400 = 1,600 is the difference between the upper and lower yearly counts.

Spot the difference

In the figure : In the figure earthquakes are caused by volcanic eruptions, the stress of big dams, mining, underground atomic tests and water that turns to steam in the great heat inside cracks.

Rule 1: Causes — Volcanic eruption, the stress of big dams on the earth, mining, underground atomic tests, and water seeping through cracks that turns to steam in the great heat and tries to escape.

• Easy : A volcano erupting can shake the nearby ground.
• Medium : Deep mining changes the stress on rocks, which can cause tremors.
• Exam-type : Water turning to steam inside cracks tries to escape, and this pressure shakes the rocks.

In the figure : In the figure earthquakes destroy buildings, roads and railways, cause fires in cities, make tsunami waves under the ocean, and change the course of rivers and the water-table level.

Rule 2: Effects — Loss of human beings, wild animals and pets; large economic loss (poles, pipelines, houses, roads, railway tracks); destruction of ecosystems and loss of biodiversity; changed river flow; chance of fire in cities; tsunami; change in the water-table level.

• Easy : A broken gas pipe after a quake can start a fire.
• Medium : A river can change its path because the land has moved.
• Exam-type : An under-ocean earthquake pushes a huge amount of water and makes a tsunami that hits distant coasts.

Spot the difference

In the figure : In the figure during an earthquake take cover and stay put, use the stairs and not the lift, and afterwards use a torch, not candles. Do not wait near tall buildings or electric poles.

Rule 1: Safety during and after — At home do not get scared or run around: stay in one place, sit on the floor or under a bed or other furniture and cover yourself until the shaking stops. If there is no shelter, sit in a corner and cover your head with your hands. In a vehicle or outside, park at a safe place and sit inside; do not wait near or below tall buildings, trees or electric poles. Avoid the lift and use the staircase. After the quake, switch off the main electric supply and use a torch or battery, not candles, lanterns or matchboxes.

• Easy : Sit under a sturdy table, cover your head, and stay until the shaking stops.
• Medium : If outdoors, move away from poles and tall buildings to an open area.
• Exam-type : After an earthquake there may be a gas leak; do not light a match or candle and switch off the main supply.

In the figure : In the figure earthquake resistant buildings, built to the codes of the Indian Standard Institute, are not damaged by earth movements up to a certain limit.

Rule 2: Resistant buildings — They are built using advanced technology to the codes of the Indian Standard Institute (IS 456, IS 1893, IS 13920). Instruments like the laser ranging, creep meter, strain meter and tilt meter give prior warning.

• Easy : IS 1893 is a code for earthquake resistant design.
• Medium : A building made as per the codes may crack slightly but is unlikely to collapse.
• Exam-type : When building a house, ask the engineer if the design follows the earthquake codes.

Spot the difference

In the figure : In the figure fires are of five classes: A solids, B liquids, C gases, D combustible metals and E electrical fires.

Rule 1: Classes of fire — Class A: solids (wood, clothes, coal, paper), put out with water. Class B: liquids (petrol, oil, varnish, paints), lighter than water, so fire extinguishers are used. Class C: gases (acetylene, LPG). Class D: combustible metals (potassium, sodium, calcium) which react with water. Class E: electrical fires; cut off the power and use non-conductive extinguishers like carbon dioxide.

• Easy : Burning paper is class A.
• Medium : A petrol fire is class B; water is not used because petrol is lighter and spreads.
• Exam-type : A burning LPG leak is class C; a short circuit fire is class E.

In the figure : In the figure a fire can be put out by cooling it with water, by suppressing it with sand, soil or froth that cuts off air, or by keeping flammable substances away.

Rule 2: Three ways to put out fire — (1) Cool out with water. (2) Suppress the fire with sand, soil or froth that cuts off air; useful for oil and electrical fires. (3) Keep away flammable substances. The stirrup pump is the best device for small fires.

• Easy : Sand on a small oil fire cuts off the air.
• Medium : Covering a burning pan with a lid cuts off oxygen and puts the fire out.
• Exam-type : Switching off the power during an electrical fire removes the source before using a CO₂ extinguisher.

In the figure : In the figure, for fire safety, switch off the gas regulator and the appliances, shout to alert others and call the fire brigade.

Rule 3: Fire safety — Switch off the gas regulator when not in use, especially at night. Switch off appliances when going out. Shout to alert others. Call the fire brigade (101 in India). Give first aid by making the patient comfortable and calling a doctor.

• Easy : Close the LPG regulator before going to bed.
• Medium : Shout 'Fire!' loudly so that others can leave the building.
• Exam-type : Call the fire brigade at once instead of trying to fight a big fire by yourself.

Spot the difference

In the figure : In the figure rain water enters the cracks in hard rock, the rocks become heavy and slide down the slope. This landslide can block roads.

Rule 1: How a landslide happens — Natural cracks in hard rocks let rain water in, causing weathering. The rocks become heavy and slide down the slope.

• Easy : Wet soil on a steep slope is heavy and unstable.
• Medium : Roots of trees hold soil together on a slope.
• Exam-type : During monsoon, hill roads are watched for cracks and slips.

In the figure : In the figure landslides are caused by heavy rain, cutting of trees, digging for roads in mountains and the after-effects of earthquakes.

Rule 2: Causes and effects — Causes: after-effects of earthquakes, tsunami, heavy rain, storms and floods; unlimited cutting of trees causing soil erosion; digging for roads in mountains. Effects: floods and changed river paths, displaced waterfalls, artificial reservoirs, loss of life and money, blocked traffic and destroyed plant life.

• Easy : Cutting trees on a hill makes the soil loose.
• Medium : A landslide can dam a river and make a temporary lake.
• Exam-type : Planting trees on slopes is a good way to reduce landslide risk.

In the figure : In the figure a school disaster management map shows the buildings, entrance, danger spots and safe places, and must be displayed at the school entrance.

Rule 3: School disaster plan — It has a chart with basic information, a School Disaster Management Committee, details of the building and ground, hazards, and a disaster management map showing buildings, entrances, danger spots, safe places and the nearest road. The map must be at the school entrance. A mock drill (सराव कवायत) is held every month, noting the date, time, number of students and shortfalls. The Government of India, with the Indian Mountaineering Institute and ICIMOD, has started a programme to forecast landslides.

• Easy : The map shows the nearest safe place to run to.
• Medium : A mock drill each month for 12 months means 12 practices a year.
• Exam-type : If 480 students assemble in 6 minutes in a drill and the target is 5 minutes, the school is 1 minute late and notes this as a shortfall.

Spot the difference