Hundreds of volunteers, many covered in fake blood, are taking part in a massive subway disaster exercise in Britain, as emergency crews try to simulate what might happen if a high-rise tower crashed down on Waterloo station, the country’s busiest.

Seven subway cars were buried in rubble for the exercise, with hundreds of volunteers’ bodies strewn amid debris in an unused power station on the outskirts of London, according to the Daily Mail. A replica of Waterloo station was built and then destroyed at the power station. 

The exercise, said to be the largest ever in Britain, began Monday and will last four days.

Over 250 emergency first responders are participating in the exercise, including police, firefighters, and forensic specialists, some of whom are also working at a specially-constructed “temporary mortuary,” according to the BBC.

“It’s not often we get to test working practices on such a scale,” Chief Constable Debbie Simpson told the BBC.

The London Fire Brigade coordinated the exercise, which also included responders from four other countries. “Although this scenario is not a terrorist attack, we will be practicing procedures and systems that are common to any emergency that results in a large number of fatalities and injuries,” London Fire Brigade Commissioner Rob Dobson told the Daily Mail. 

The training exercise looks stunningly realistic: