How can one failed wall bring down a whole corner of a tower?

A tall building is supposed to be a team: if one part fails, the others should pick up its load. Ronan Point in East London showed what happens when they cannot. On 16 May 1968, a gas explosion in an 18th-floor corner flat blew out a load-bearing wall, and one entire corner of the 22-storey tower collapsed. Four people died and 17 were injured. Engineers call this progressive collapse: a primary structural element fails, the failure spreads to adjoining elements, and the damage ends up out of proportion to the original cause.

At about 5:45 am, resident Ivy Hodge went into her kitchen to make a cup of tea and lit a match for her gas stove. Gas had been leaking, and the match sparked an explosion that blew out the flank wall, a wall that had been supporting the four flats above. With it gone, the floors above her living room were unsupported and fell, and the falling slabs stacked onto the floors below. The tower had only been open for two months.

The cause of the gas leak was small: a cracked nut on the stove's connection, believed to have been overtightened. But the failure was not. An investigation found that the connection between floor slabs and flank walls had not been designed to cope with the changes in load from forces such as an explosion or high winds. The low death toll is thought to be due to the early hour, when most residents were in their bedrooms rather than the living rooms that collapsed. Hodge herself survived, knocked unconscious in her kitchen by the blast.

The consequences ran far beyond one tower. Britain changed its building regulations so that, in an accident, a building must not suffer collapse out of proportion to the cause, and many other countries have since done the same. Public confidence in the safety of tall residential blocks was irreparably shaken.