Spanish authorities early Friday lifted all restrictions for all 60,000 people urged to stay indoors after a chemical explosion a day earlier at a warehouse sent a large, toxic orange cloud floating above six towns.
Catalonia's regional civil protection department ended the alert about 15 hours after the accident in northeastern Igualada, when products being delivered to a warehouse were somehow mixed and exploded.
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Six people received light injuries but only one remained hospitalized Friday with leg burns.
The blast prompted authorities to order 60,000 people in Igualada and five surrounding towns to stay inside, and roads were closed leading into Igualada, about 70 kilometers (40 miles) northwest of Barcelona.
Those restrictions were lifted for most people a few hours after the cloud emerged.
But authorities kept in place until early Friday morning the order to stay inside for the elderly, small children, pregnant women and people with respiratory problems.
Igualada Mayor Marc Castells said human error apparently caused the accident at the warehouse of the chemical plant.
The civil protection department said the chemicals included nitric acid and ferric chloride.
Investigators were trying to determine if the low-lying cloud produced by the explosion was nitrogen dioxide, said a department spokeswoman who spoke on condition of anonymity because of rules preventing her being quoted by name.
Nitrogen dioxide has the same color as the cloud that was seen over the towns, can be produced with explosions involving nitric acid and is toxic when inhaled.
The foul-smelling gas is also produced by motor vehicle exhaust, burning of fossil fuels and nuclear bomb tests — giving mushroom clouds their orange and reddish color.