While a convenience store was having a disabled access ramp constructed, two elderly customers fell over it and suffered broken bones.
It cost the contractor building the ramp a £600,000 fine with £11,520 costs just before Christmas.
The contractor was Martin McColl Ltd, who was working for JMS Retail Concepts Ltd. Both were sentenced when they appeared before Cardiff Magistrates on 22 December.
The Court heard that during the three-days it took to build the concrete ramp access to the store in Dinas Powys, Vale of Glamorgan, in January 2016, two members of the public were injured while attempting to enter the store.
On 12 January an elderly woman tripped over the construction work, breaking her wrist, hitting her head and suffering severe bruising.
The next day, an elderly man fell from the partially constructed ramp, breaking his collar bone and suffering severe bruising.
An investigation by the Health & Safety Executive (HSE) found that construction work being undertaken while the store remained open meant customers were required to walk through the construction site to enter and exit the store.
It would have been reasonably practicable to close the store during the construction of the ramp and install barriers and signs to prevent access by members of the public, determined HSE.
Martin McColl Ltd of Ashwells Road, Brentwood, Essex, pleaded guilty on the first day of two allocated for the trial (having initially pleaded not guilty) to breaching Section 3(1) of the Health & Safety at Work (etc) Act 1974. The company was fined £600,000 and ordered to pay costs of £11,520.
JMS Retail Concepts Ltd of Stump Lane, Chorley, Lancashire, pleaded guilty to breaching Section 3(1) of the Health & Safety at Work (etc) Act 1974. It was fined £40,000 and ordered to pay costs of £3,038.
After the hearing, HSE inspector Gemma Pavey said: "These incidents could so easily have been avoided by simply carrying out correct control measures and safe working practices.
"Commercial clients and companies should be aware that HSE will not hesitate to take appropriate enforcement action against those that fall below the required standards."