The Leiden Explosion of 1807

By Peter Douglas

In 1807 the Netherlands, though officially an independent kingdom, was a satellite state of France, then ruled by Napoleon Bonaparte. The emperor had installed his brother Louis as ruler of the Kingdom of Holland in 1806. The country was thus France’s ally in its war with England. Invasion was anticipated, so the stock of black powder in the central magazine in Delft had to be replenished. To this end, in late 1806 the country’s twelve gunpowder factories were ordered to produce without delay a quarter of a million pounds of black powder.

In January 1807, a convoy of three civilian ships chartered by the government sailed from Delft to Amsterdam to fetch the first shipment from seven of these factories and take it to the central army magazine. In charge of the convoy was a government official, Bartholomeus Hendrik Bobbink. The ships arrived in Amsterdam on January 6, and one of them, the Delfs Welvaaren, meaning Prosperity of Delft, took on 36,900 pounds of gunpowder in 369 100-pound barrels. Bobbink instructed the crew to sail to Leiden and wait outside the city while he accompanied the other two ships to the powder factories north of Amsterdam. These two ships would sail to Leiden after loading the rest of the powder kegs, and then the three ships, under Bobbink’s supervision, would travel together from Leiden to Delft.

The Delfs Welvaaren arrived at the bridge over the Haarlem-Leiden canal on January 10. Meanwhile, very cold weather had come to the north, and Bobbink and the other ships got trapped when the canals froze. He gave orders to the Delfs Welvaaren crew not to wait for the rest of the convoy but to sail on to Delft. On the morning of January 12, they left their berth and entered the city of Leiden, mooring in the Steenschuur, a canal in a wealthy neighborhood.

Soon after four o’clock that afternoon the ship exploded with a force of 20,000 pounds of TNT, creating a superheated 50-meter fireball and a powerful shockwave traveling faster than sound. Bits of wood and metal from the obliterated ship were found at great distances from the canal. The anchor was found near the Hogewoerds gate, 900 meters away. The mast’s heavy lead counterweight was thrown 500 meters, and the mutilated remains of a crewmember were found 700 meters from the ship.

In addition to the ship’s crew, the explosion killed 151 of Leiden’s citizens, and some 2,000 were injured. Most of the victims met their death due to collapsing buildings. The weather and time of day contributed to the deadly nature of the explosion—January 12 was not a very cold day, but it was winter and by dusk most people were indoors, with the result that many were buried in the ruins of their houses.

Louis Bonaparte took his duties as king seriously, and he visited Leiden to inspect the damage. His concern, actions, and generosity during the relief efforts, as well as during a severe flood in 1809, earned him the people’s devotion and respect, and the name Louis the Good.

The city council ordered an immediate inspection of the disaster area to assess the damage and determine which buildings could be saved and which had to be demolished. An area of over thirteen acres was devastated. The houses within 120 meters of the explosion, about 220 buildings, were totally gone or their unrepairable remains had to be pulled down as a precaution. Beyond this and up to 170 meters, most of the buildings were destroyed or seriously damaged. Heavy damage was inflicted at greater distances too, even near the city limits, and Leiden’s main churches, the town hall, and other significant structures suffered badly. Everywhere buildings were windowless and roof tiles littered the streets. Disaster brings progress, and within three months of the explosion, stricter new laws were passed concerning the safe storage and carrying of black powder, which could no longer be transported through densely populated areas.

As to the cause of the explosion, at first the government supposed it to be an act of sabotage or terrorism, possibly signaling the start of an English invasion. Given how devastating the explosion was, along with the limited capacity of forensic investigation at the time, no sure confirmation of the cause was ever found. The leading theory is that the disaster had been caused by the carelessness of the ship’s crew.

Contemporary safety standards dictated that such a cargo must be protected with fire-resistant horsehair sheets, and the ship’s hatches had to be covered with a tarpaulin. Moreover, the crew was forbidden to enter the ship’s hold during the voyage. Eyewitnesses testified that that shortly before the explosion they had seen someone throwing potato peels overboard, so it was thought that the crew was preparing a meal. On the basis of this evidence it was reasoned that the explosion was a result of the crew’s appalling negligence with a cooking fire in the vicinity of the powder kegs. Black powder ignites very easily, and one spark would have been enough.

One witness, Jan Overduin, a dredger cleaning out the canal some hundred yards from the ship, and who had miraculously survived, confirmed that the crew had been preparing food. The dredger also told the authorities that he had seen two separate explosions, a small one that lifted the mast and threw the hatches into the air, followed almost immediately by a second massive explosion. This suggests another possible explanation.

With the country at war, gunpowder fetched a good price on the black market, so the temptation to take a small quantity from the cargo must have been strong. If this occurred, it’s possible that the crew may have set one keg of powder aside and opened it to steal some of the contents. By imprudently using metal tools or wearing shoes with nails in them, they may have created a spark that set off this separate keg, resulting in the first small explosion, and then the other 368 barrels ignited. The authorities looked into this and some allegations were brought against the crew, but this line of investigation was abandoned once it was confirmed that all three of the crew had been killed.

This was certainly not the only black powder explosion in the Netherlands over the centuries, though it was the worst in terms of the number of casualties. In the “Delft Thunderclap” of 1654, a magazine containing 85,000 pounds of powder exploded, but fewer died. Apart from accidents in powder factories, carelessness, ignorance, attempted theft, and even lightning caused magazine explosions in several cities: Leiden (1481), Bredevoort (1646), Delft (1654), Heusden (1680), Maastricht (1761), and Amersfoort (1787).

In a number of these cities it is still possible to make out in a town square or a small park the empty spaces left by these disasters. In Leiden it is Van der Werfpark, a green and pleasant park full of trees and winding paths and a statue of Pieter Adriaansz van der Werff (1529-1604), the mayor of Leiden who defended the town against the Spanish in 1574 and inspired the citizens. Since 1886 the park has occupied the site of the Grote Ruïne opposite where the doomed ship was moored.