ONE of the country's leading medical research units has admitted breaching safety regulations after the death of an experienced laboratory worker.

Mr James Graham, 51, was asphyxiated when liquid nitrogen gas filled his laboratory as he carried out a routine task. He had worked with the gas, used to freeze biological samples, for a decade.

The Medical Research Council (MRC), which aims to improve human health, admitted failing on a number of safety measures including inadequate ventilation, failing to ensure a warning alarm was switched on and failing to install a safety device to control a liquid nitrogen storage tank.

The lives of other staff members at the MRC-run Human Genetics Unit based at the Western General Hospital in Edinburgh were also endangered, but they survived.

Edinburgh Sheriff Court heard yesterday that Mr Graham died when about 700 litres of liquid nitrogen leaked into a freezer room, depleting the oxygen in the air.

Fiscal depute Liz Paton told Sheriff Iain MacPhail, QC, that staff member Ruth Suffolk, 41, had gone into the room at about 9.15am. She heard a hissing noise and saw a cloud of vapour in a corner of the room.

She then found Mr Graham collapsed on the floor, unconscious and frozen. Liquid nitrogen was streaming out of a hose attached to the wall.

Ms Suffolk staggered from the room, banging her head. She was able to turn off the liquid nitrogen supply and summon help before passing out on top of Mr Graham.

Employee Stewart McKay, 37, raced into the room and dragged Ms Suffolk to the middle of the floor before leaving for fresh air. Staff member Agnes Gallagher, 43, dragged Ms Suffolk the rest of the way into the corridor.

It took Mr McKay several attempts with the aid of other colleagues to pull Mr Graham from the room but he never regained consciousness.

It was Mr Graham's job to fill two storage vessels inside the unit from a tap controlling a 2000-litre tank of liquid nitrogen outside the building connected by a metal hose. He would then pump the chemical into flasks and various tanks, where human tissue samples used for research into diseases were kept frozen.

On October 25, last year, he was filling the tanks from both internal storage vessels at the same time, an unapproved procedure, after switching off a safety alarm that measured oxygen levels. Because Mr Graham was at times exposed to low levels of oxygen during his work, the alarm would have gone off continuously while transferring the liquid nitrogen to the various containers.

Mrs Paton said: ''It appeared that James had filled two storage vessels, had emptied one in the process of filling the tanks and was still finishing the tank when he opened the main inlet valve to fill other flasks. At which point it is feasible that the oxygen levels in his breathing zone were substantially depleted, something he would not be aware of as the alarm was inhibited.''

Although designed as a liquid nitrogen store room in 1997, the lab had no windows apart from a panel in the door, and the ventilation system in place was inadequate to cope with a major leak.

There was also no safety valve on the external tank to automatically stop an excess of liquid nitrogen pouring into the freezer room when the level of oxygen dropped dangerously low.

Defending, Mr Derek Batchelor, QC, said that the MRC had taken steps in all its establishments across the UK to overcome the problems that led to this death.

He listed improvements including installation of a tank safety valve, a new system to automatically fill internal storage tanks with liquid nitrogen, safety assessments, better ventilation, new regulation for employees to work in pairs, more staff safety training, personal oxygen monitors and a warning never to mute an alarm. A full-time health and safety manager had also been appointed.

MRC managers expressed their deepest sympathy for Mr Graham's family, friends and the staff at the unit.

Sheriff MacPhail will sentence MRC today after considering the facts.