Three men are recovering after being rescued by firefighters after blacking out in a huge steel silo containing waste food at a recycling plant.

Fire crews were called to the Kingshill recycling depot, near Cricklade, Wiltshire, on Thursday after workers feared three of their colleagues were trapped inside the container.

It later emerged that one worker had been overcome through lack of oxygen as dangerous fumes had built up inside the silo and then two fellow workers who went to help suffered the same fate.

Firefighters wearing breathing equipment entered a trapdoor in the side of the 20ft-high vessel before hauling the trio to safety where they were given emergency oxygen.

Tragedy may have resulted at the depot, which is alongside the A419 Swindon to Cirencester road, had the rescuers not been quickly alerted.

The drama happened at the same large complex, although it is run by a different company, where a 33-year-old recycling worker was crushed to death in an accident three years ago.

Wiltshire Fire and Rescue Service was called shortly after noon on Thursday to the Kingshill centre, one of Wiltshire's oldest and best-known recycling plants.

A statement from the brigade said: "Upon arrival it became apparent that all three employees were still inside the vessel.

"Firefighters wearing breathing apparatus entered a trap door in the side of the silo and quickly rescued all three of the workers.

"Emergency first-aid was administered on scene and all three casualties were revived with oxygen and transported to Great Western Hospital in Swindon for treatment."

An investigation was mounted into the incident which was thought to have been caused by a deficiency of oxygen, the result of fermentation of the waste within the silo.

Yesterday, fire station manager Pete Townsend, the brigade's HAZMAT (Hazardous Material) adviser, explained that bacteria from food waste consumed oxygen as it fed and multiplied. "Carbon dioxide, an asphyxiant gas that can kill, is then generated as a byproduct," he said.

Mr Townsend said a worker was repairing a stirring paddle inside the silo when he blacked out and collapsed and that two of his colleagues who went to his aid and also fell unconscious.

He said: "Carbon dioxide is colourless and odourless and the workers would have had no warning of the potentially fatal situation they were in."

The incident was attended by five fire appliances, several ambulances and a police helicopter, which was used to transport specialist air sampling equipment to the site.

The brigade added that is was anticipated that all three men, who have not been named, would make a full recovery and should suffer no long-term ill effects from their experience.

The plant has been run by Wiltshire recycling pioneers the Freeth family for nearly 40 years.

Plant boss Richard Freeth was unavailable for comment yesterday. A company spokesman said: "There is no one available for comment and there won't be at any time."

Tragedy struck on August 16, 2005 when former soldier Paul McGuire died from multiple injuries after falling into a cardboard baling machine at a part of the complex operated by recycling giant Sita.

Sita, which operates separately from the Freeth section of the site, is now being prosecuted for negligence under Health and Safety at Work regulations following Mr McGuire's death.