The man died after liquid nitrogen spilled in a basement storage room of the Medical Research Council's Human Genetics Unit in the hospital complex.

The BBC's Liz Mackean: "It is still not known how this man died"

It is not known if his death resulted from a medical condition or as a result of the chemical leak.

Four other were treated for the effects of inhaling chemicals and were later discharged. One was also treated for cuts to the head.

Prof Hastie: "Deeply distressed"

About 40 people were evacuated from the four-storey block, but emergency services said the leak had been confined to a storage room and there had been no danger to the rest of the hospital.

The Health and Safety Executive said it had launched an immediate investigation into the death.

The centre is a world leader in research into human genetics and the substance involved was used to store human tissue at a sub-zero temperature.

In a statement, the MRC said it was "deeply distressed" by the death of a member of its staff.

BBC Scotland's Morag Kinniburgh: "The man was working in the basement storage unit..."

Unit director Professor Nick Hastie, stressed the liquid nitrogen had not leaked outside the building.

Referring to the dead man, Professor Hastie said: "This was a person who has worked daily with liquid nitrogen for years.

"It poses no threat, it's an inert substance and he used it regularly for our experiments."

'Not dangerous'

Lothian and Borders Fire Brigade spokesman Ross Wynn said: "Nitrogen gas itself is not dangerous - 80% of the air is made of nitrogen.

"But in a confined space it can be dangerous or in close proximity to the liquid gas, you could get cold burns."

A spokesman for Lothian and Borders Police said the dead man, whose name would not be released until his relatives have been informed, was a laboratory assistant.

The Human Genetics Unit, established in 1967, is one of the MRC's largest research establishments, supporting about 220 scientists and staff.

The unit is at the forefront of research into human genetics. Its role is to advance the understanding of genetic factors implicated in human disease.