The Court at the Old Bailey heard that the men were constructing a large steel structure as part of the foundation for a large Pressure Test Facility (PTF) at Claxton Engineering Services in Great Yarmouth.
The structure, which weighed several tonnes, collapsed on top of the group. A large-scale emergency response took place to try and rescue the trapped workers. Adam Taylor, 28, 41-year-old Peter Johnson and brothers Thomas Hazelton, 26 and Daniel Hazelton, 30, were all pronounced dead at the scene.
The excavation for the horizontal PTF was more than 23m long, 3m wide and 2m deep. The horizontal steel cage being constructed would have weighed about 32 tonnes when completed.
The group were working for Hazegood Construction Ltd. Daniel Hazelton was an employee, while the other three were self-employed contractors. Encompass Project Management Ltd was the principal contractor, with Hazegood operating as a contractor.
A Health and Safety Executive (HSE) investigation found serious flaws in the planning, management and monitoring of this complex project on the part of Claxton as well as Encompass and its company director David Groucott.
Claxton Engineering Services Ltd of Ferryside, Ferry Road, Norwich pleaded guilty to breaching Regulation 9(1)(a) of the Construction (Design and Management) Regulations 2007. The company was fined £500,000 and ordered to pay costs of £100,000.
Encompass Project Management Ltd of The Gables, Old Market Street, Thetford, Norfolk pleaded guilty to breaching Section 3 (1) of the Health and Safety at Work etc Act 1974. It was fined £200,000 and ordered to pay costs of £50,000.
David Groucott of Diss, Norfolk, pleaded guilty to breaching Section 37(1) of Health and Safety at Work Act. He was sentenced to a seven and a half month custodial sentence, suspended for two years. He was ordered to complete 200 hours of unpaid community work within 12 months, and also ordered to pay costs of £7,500.
Charges against Hazegood Construction Ltd were ordered to lie on file.