Oil and chemical plants run by INEOS at Grangemouth have breached health and safety regulations 34 times in the last four years, been officially condemned as "poor" for pollution for three years in a row, and seen more than 20 staff injured since the start of 2015.

An investigation by the Sunday Herald has uncovered the Swiss-based petrochemical giant's record of mishaps, leaks and failures to control risks for workers.

The revelations have prompted criticisms from environmentalists and trade unionists, who claim that safety at Grangemouth has deteriorated. They will also increase anxieties over INEOS's bid to win community and political support for fracking shale gas across the central belt.

The fears are, however, dismissed as "baseless" by INEOS. Grangemouth has one of the best safety records in the chemicals industry and 2014 was its best ever year, the company says.

However, failing to reduce the dangers of pipes degrading in 2011 could have led to a major accident, according to the government's Health and Safety Executive (HSE).

INEOS has been served 11 legal enforcement notices by the HSE for breaking the rules 34 times at Grangemouth between 2011 and 2014. This compares to just three notices over the previous four years from 2007 to 2010.

In 2013 HSE said that there was a "lack of suitable and sufficient risk assessment ... associated with the over-pressurisation of vessels", such as gas tanks. In the same year "adequate control measures to prevent emission of hydrogen sulphide" had not been implemented, it said.

In 2012 there was "a failure to ensure that stress critical small bore pipework was adequately designed, supported and maintained". And in 2011 HSE pointed out that a "risk of uncontrolled pipework/pipeline degradation leading to a major accident has not been reduced so far as is reasonably practical".

The original compliance dates for many of the improvement notices slipped, but ten have now been complied with. The eleventh, issued in October 2014 for failing to ensure timely examination of containers, like tanks, and pipework, is currently due to be resolved in April.

The pollution performance of INEOS's Grangemouth oil refinery was rated as "poor" by the Scottish Environment Protection Agency (Sepa) in 2010, 2011 and 2012.

According to Sepa, there were "unabated emissions via an unauthorised emission point" at the refinery in 2012. There was a "significant breach of the permit due to poor operational control during a plant upset" in 2011.

However, the company stressed that its pollution performance was also classified as "broadly compliant" and "excellent" under different pollution regimes, while other company operations were assessed as "good" or "excellent".

Information leaked to the Sunday Herald shows that nearly 400 safety incidents have been reported within INEOS at Grangemouth since the start of January. There have been over 20 injuries to workers, including burns, slips and falls.

In February the company's chemical director, Gordon Milne, sent staff a circular warning that 2015 had started with "a really poor safety performance" causing too many colleagues to be injured. Everyone needed to "get a grip" to make sure that more people weren't hurt, he said.

The trade union, Unite, claimed that the number of union health and safety representatives at Grangemouth had dropped from 64 to single figures. "There has been a sizeable exodus of experienced labour and expertise from the site over the last eighteen months," said general secretary, Pat Rafferty.

"Our concern is that ensuring the safe operation of the site was challenging enough even with the presence of a fully-trained and recognised trade union workplace safety team."

Friends of the Earth Scotland slammed INEOS's safety history, and called for more investment to improve staffing and maintenance. "Communities will be looking at INEOS's poor record at Grangemouth when they judge for themselves the trustworthiness of the company's claims that fracking is safe," said the environmental group's Mary Church.

INEOS stressed that its safety record worldwide was twice as good as the industry average and was continuously improving. "Safety, health and environment performance is the company's highest priority," said a spokesman.

"We are committed to ensuring that our facilities have as low an impact as possible on local people and the environment and we continue to work in close partnership with community groups and other stakeholders to ensure that we are a responsible neighbour."

Grangemouth's petrochemicals business had reduced emissions to air and water by 45 per cent in 2014, he added. "To suggest that INEOS does not invest sufficiently to ensure good safety, health and environmental performance is simply baseless."

HSE described the number of improvement notices at Grangemouth as "not exceptional" given the size and complexity of the site. It hadn't needed to ban work from taking place because none of the breaches presented an "immediate risk".