Sunday, December 11, 2005, was a day without sun for many Londoners. At about 6 a.m. local time, an explosion rocked a fuel depot in Hertfordshire, approximately 40 kilometers (25 miles) north of London. The ensuing oil fire sent thick clouds of sun-blocking black smoke billowing over London and South England. By 11:50 a.m., when the Moderate Resolution Imaging Spectroradiometer (MODIS) flew over on NASA’s Terra satellite, the smoke had fanned south over tens of kilometers. London, normally a large cement-colored circle on the landscape, was not even visible beneath the smoke. Nearly three hours later when Aqua MODIS flew over, the fire was still burning, and the smoke had spread still farther.
The extent of the smoke is easier to see in the false color images, which were created using light from the shortwave and near infrared part of the electromagnetic spectrum. In these images, the dark smoke stands out clearly against the brilliant green of the plant-covered land. At the source of the smoke, the intense heat of the fire glows red in the infrared. According to news reports, the fire was the largest industrial fire ever seen in Europe.
By December 12, the smoke had thinned to a single plume. The dark plume of smoke that blows southwest from the fire blends with the green and tan of the underlying landscape. It is easiest to see from the shadow it casts on the ground. Skies over the London metropolitan area, the cement-grey area southeast of the fire, are clear, an improvement from December 11 when the smoke entirely obscured the city from view. The smoke contained small particles, soot, which can cause irritation when inhaled. For this reason, British health officials advised people near the blast to remain indoors. The smoke also contained gases like carbon monoxide, carbon dioxide, and sulphur dioxide. For more information about the health impacts of the smoke, see the Health Protection Agency web site.