Hazard, vulnerability, risk and disaster
A hazard is something that can cause harm: a flood, earthquake, cyclone, landslide, fire, chemical leak or epidemic. Hazards can be natural or human-made (technological).
Vulnerability means how easily people get hurt: weak houses, homes on flood plains, no warning system, poverty. Capacity is the opposite: skills, money and plans to cope.
Risk = hazard × vulnerability ÷ capacity. A disaster happens when a hazard hits and the community cannot cope with its own resources. The same earthquake can be a small event in a prepared city and a disaster in an unprepared one.
The disaster management cycle
- Mitigation (long before): reduce the danger. Build earthquake-safe houses, embankments and drains; do not build on flood plains; plant mangroves on coasts.
- Preparedness (before): plans, drills, warning systems, shelters, trained volunteers and an emergency kit: water (about 3 litres per person per day for 3 days), dry food, torch, radio, batteries, first-aid kit, medicines, copies of documents, whistle, power bank.
- Response (during and just after): warnings, evacuation, search and rescue, first aid, shelter, food and water.
- Recovery (after): repair homes, schools and roads, restart jobs, support mental health, and "build back better" so the next event hurts less.
Many groups work together: government emergency agencies, fire and police, army, hospitals, the Red Cross/Red Crescent, schools and ordinary citizens.
Warnings and evacuation
Early warning uses sirens, phone alerts, radio, TV and loudspeakers. Learn your local signals; many places use a rising-and-falling siren for danger and a steady tone for all-clear.
When told to evacuate:
- Stay calm and follow official instructions only (not rumours).
- Take your emergency kit; switch off gas and electricity if safe.
- Follow the marked evacuation route to the assembly point or shelter; help children, old and disabled people.
- Do not go back until officials say it is safe.
If you cannot leave, shelter in place: go to a safe room (upper floor for floods, inner room with closed windows for chemical leaks).
Emergency numbers: 112 works across the EU and India; many countries also use 911 or 999.
What to do for specific hazards
- Flood: move to high ground. 15 cm of fast water can knock you over; 30 cm can float a car. Never walk or drive through it. Avoid electric wires.
- Earthquake: Drop, Cover, Hold on under a strong table; stay away from windows. Outside, move to open ground away from buildings and wires. Expect aftershocks.
- Fire: raise the alarm, call for help, stay low under smoke, feel doors with the back of your hand before opening, use stairs not lifts. Clothes on fire: Stop, Drop, Roll. Small fire: use the right extinguisher only if trained.
- Cyclone/storm: stay indoors away from windows or go to a cyclone shelter; secure loose objects.
- Chemical leak: go indoors, close windows and vents, listen to the radio.
- Tsunami: if the ground shakes strongly near the coast or the sea pulls back, run to high ground at once.
Key formulas and definitions
- Risk = Hazard × Vulnerability ÷ Capacity
- Cycle: Mitigation → Preparedness → Response → Recovery
- Earthquake: Drop, Cover, Hold on
- Clothes on fire: Stop, Drop, Roll
- Water in kit: about 3 L per person per day, for at least 3 days
- Emergency number 112 (EU, India)
Worked examples
1. A family of 4 wants 3 days of water in their kit. How much water do they need?
3 L × 4 people × 3 days = 36 litres.
2. Two towns have the same flood hazard. Town A has an embankment, warnings and a shelter; Town B has none. Which has higher risk?
Town B. Same hazard, but higher vulnerability and lower capacity, so higher risk.
3. Put these in the right stage: building a seawall, a school fire drill, rescuing people from rooftops, rebuilding a bridge.
Seawall = mitigation; fire drill = preparedness; rescue = response; rebuilding = recovery.
Common mistakes
- Thinking a hazard and a disaster are the same. A hazard becomes a disaster only when people cannot cope.
- Running outside during strong earthquake shaking. Drop, Cover, Hold on first.
- Walking or driving through flood water because it looks shallow.
- Going back to collect things during an evacuation, or using a lift in a fire.