London ? The flames are finally out at the enormous oil depot fire north of London, but they have set off a blaze of questions about safety at huge chemical and industrial plants around the country.

Experts are questioning the wisdom of allowing such potentially dangerous installations in densely populated areas. The country’s five biggest oil depots are in or near major metropolitan areas, meaning an accident or terrorist attack could be potentially catastrophic.

Some critics also worry that emergency services are insufficiently prepared for such disasters.

The series of explosions Sunday at Buncefield, 25 miles outside the capital, came four days after an al-Qaida videotape appeared on the Internet calling for attacks on facilities carrying oil. However, officials drew no link between the two events, and the blasts are being treated as an accident.

The explosions injured 43 people and created huge plumes of thick, black smoke that drifted as far as France. Two thousand people were temporarily displaced and 20,000 workers were shut out of their jobs at a nearby industrial park.

Though safety procedures at oil depots are generally rigorous, it is impossible to eliminate risk at facilities storing large amounts of volatile fuel.

The dangers posed by those facilities have increased in recent years, with suburban sprawl placing people ever closer to the plants. When it was built in 1968, the Buncefield depot was surrounded by farmland.