A series of explosions and fires on the Piper Alpha, an oil platform 110 miles off the coast of Scotland that had been converted to natural gas production, results in the deaths of 167 people and the collapse of the platform.

• Note: Only episode with the opening narration being "sequence of critical events, locked in time".

As the World Trade Center in New York City burns after being hit by two hijacked aircraft, another hijacked aircraft is deliberately flown into The Pentagon, killing all 64 people on board and 125 on the ground.

• Note: Only episode with the opening narration being "don't just occur".

At the Austrian alpine village of Galtür, snow on the mountains surrounding the village build up. Due to the changing temperature during the month, a strong but brittle layer of ice forms under the snow. On the day of the disaster, the ice layer collapses and the building ice bank slips down the slope and forms a powder avalanche. Two minutes later, it hits Galtur and buries 57 people in the snow, killing 31 of them.

• Note: opening narration changed to "unravel the fateful moments".

British Midland Flight 92, a two-month-old Boeing 737-400, takes-off from Heathrow Airport in London, heading for Belfast. While on route the aircraft's left engine suffers a fan blade failure. The crew shut down the wrong engine and start to prepare for an emergency landing at East Midlands Airport. On approach to the airport the damaged left engine fails completely and then catches fire. With insufficient thrust to maintain altitude, the plane crashes 900 metres from the runway on the M1 motorway embankment at Kegworth, killing 47 people, though miraculously, the plane managed to clear the motorway itself, preventing any further casualties on the ground.

• Note: opening narration changed to "unravel the clues and count down" and used in subsequent episodes. exceptions are stated in note.

Mount St. Helens in the countryside of Washington erupts for the first time in 123 years, killing 57 people.

• Note: Only episode with the opening narration being "behind natural disasters are a chain of"

The British car ferry M/S Herald of Free Enterprise departs the port of Zeebrugge in Belgium. The crew accidentally left the bow doors open and water enters the car deck, causing the ferry to capsize, taking the lives of 193 passengers and crew.

• Note: Only episode with the opening narration being "unravel the decisions that triggered those".

The Japanese city of Kobe is rocked by the Great Hanshin earthquake, which destroys many of its buildings. Many traditional houses collapse due to the heavy roofs and weak walls. Soil liquefaction occurs at the coastal and port areas of Kobe. 6,434 people die in what is then Japan's worst peacetime disaster.

• Note: opening narration is "behind every disaster lies a chain of critical events that decides who lives and who dies".

Bombers in Bali attempt to detonate bombs in three different places. The first, a suicide bomb, is detonated in a small nightclub across the road from another nightclub, the Sari Club. A second bomb, a truck filled with explosives parked outside the Sari Club explodes 15 seconds after the first. Less than a minute later, a third bomb detonates outside the United States Consulate. The total death toll is 202.

• Note: opening narration is "behind every disaster lies a chain of critical events that decides who lives and who dies. unravel the fateful moments in those final".

For days, a foul smell hangs around in the Humberto Vidal shoe store in San Juan, Puerto Rico. The smell is caused by leaking propane gas coming from an unmapped pipe in the sloping road near the shoe store. The gas goes undetected due to faulty gas searching techniques. Then, an air conditioner with bad wiring is switched on, starting a spark that ignites the propane and the store explodes, claiming 33 lives.

• Note: opening narration is "behind every disaster lies a chain of critical events that decides who lives and who dies".

During a training mission, a torpedo on board the Kursk leaks hydrogen peroxide. It reacts with iron oxide (rust) in the bow and blasts the front of the submarine. Although the submarine has explosion-proof walls, the explosion spreads through the ventilation shafts, killing everyone at the command post and preventing the sub from performing an emergency blow. 135 seconds later, another explosion rocks the submarine. Then it sinks, killing all but 23 men on board. While the survivors wait to be rescued, special boards that produce breathing oxygen with potassium superoxide drop into the oily floor, starting a reaction that creates a fire, killing them as well.

• Note: opening narration is "triggered by a chain of critical events".

ValuJet Flight 592, a McDonnell-Douglas DC-9 with 110 people on board, is bound for Atlanta, Georgia from Miami, Florida. Suddenly a fire starts in the cabin and cockpit, so large it consumed in flames and the crew are incapacitated by the smoke. The jet loses control and goes down in the Everglades, leaving no survivors.

• Note: opening narration is "the result of a chain..".

Three air conditioning units on the roof of the five-story Sampoong Department Store in Seoul, South Korea are moved across the roof. Two years later, a column on the fifth floor fails causing the building to collapse. The store had been kept open, despite reservations about its safety, and 502 people in the store were killed.

A de Havilland DH.106 Comet 1, the world's first passenger jet airliner, takes off from Rome but explodes over the Tyrrhenian Sea 26 minutes into the flight, killing all 35 people on board. The investigation begins but three months later, another Comet crashes evidently in the same manner taking another 21 lives. All Comets are grounded and the investigation takes a step forward. The investigation results in improved metallurgical understanding, from which all aircraft design greatly benefits, even over five decades after the incidents.

The most violent outbreak of tornadoes in history, the 1974 Super Outbreak, releases 148 tornadoes in 13 American states and one province in Canada. Thousands of homes are destroyed and more than 330 people die; 5,000 people are left homeless or injured. A team of meteorologists led by Ted Fujita will examine the tragedy to provide new methods to predict more precisely the future tornadoes.

In July 1995, the Soufrière Hills volcano on the Caribbean island of Montserrat spews ash over the island. The nearby capital of Plymouth is evacuated. Two years on, Soufrière Hills erupts violently. Pyroclastic flows rage down the mountain and destroy Plymouth and Bramble Airport, killing 19 people. The eruption generates a small tsunami.