THE owners of the BP Grangemouth complex could face prosecution following a second major safety scare at the plant in less than a fortnight.

Hundreds of local people were terrifed by a huge plume of steam which erupted near a public road through the plant, creating a 90-minute series of ear-shattering bangs after a steam pipe fracture late on Wednesday night.

Grangemouth residents claimed the latest incident was one of the most frightening in living memory, while Falkirk East MP Michael Connarty said he would be demanding answers from the company at a meeting today about the fifth incident raising safety concerns in the last year at the complex.

Central Scotland Liberal Democrat MSP Donald Gorrie last night said he had written to Enterprise Minister Henry McLeish and the Health and Safety Executive, calling for a ''thorough and open inquiry.''

The HSE said it would be investigating the latest incident and a separate breakdown at the end of May involving a power station failure, which led to a controlled shutdown of the refinery, and oil and gas processing plants.

An HSE spokesman said: ''The HSE is undertaking investigations of both the power loss incident and the steam release which could lead to prosecution and it is too early to comment on the outcome of such investigations.''

Promising a ''thorough and detailed inquiry'' into the steam leak, the spokesman said the number of HSE inspectors at Grangemouth had increased in the last year and that in 1999 an improvement notice relevant to major hazard activities on the site was served and was complied with fully. He said regular meetings took place with complex directors to improve its health, safety, and environmental performance.

Last night, the Scottish Environment Protection Agency (Sepa) said it was not aware of any implications of environmental pollution.

A stretch of Bo'ness Road which runs through the complex, was closed at about 11.15pm on Wednesday as steam belched from the fractured pipe. The road remained closed yesterday and was likely to be shut off for several days as a precautionary measure to allow a full investigation of the pipe, which runs under the roadway.

BP insisted only steam had escaped and while apologising for the noise and inconvenience, claimed no-one had been in any danger. Spokesman Ken Richardson said plant production had been cut back as a precautionary measure and a full investigation was being conducted.

Mr Connarty said: ''I think there is something fundamentally wrong within the infrastructure of the site. They need to crawl over that inch by inch to make sure. They have spent #1.5bn on the site expanding it in the last eight years. It may be just overloading the old infrastructure which they need to replace.''

He said he had also received anonymous letters suggesting maintenance at the plant could be suffering as a result of job losses.

Mr Bill Simpson, chairman of the Grangemouth Area Forum said: ''BP has got an excellent track record over many years but in the last 18 months it has been badly tarnished and a question that needs to be asked is: Is that downturn in performance linked to redundancies and demanning?''

Mrs Joyce Robertson and her husband Eddie, of Duke Street, said they had been alarmed by the noise. Mrs Robertson said: ''It really was quite frightening. A neighbour in Oswald Avenue, who doesn't have double glazing, said the noise was absolutely deafening.''

Retired BP worker Jim Scott, of Bo'ness Road, said: ''I know they're doing big changes to change over to a new power station. To me, this cannot happen without some sort of incident.''