The HSE told Llandudno Magistrates’ Court that on 1 October 2014 a worker was cleaning out a pump following a concrete pour at a construction site on Colwyn Bay promenade.
He lifted the interlocked safety grille and sat on the hopper with his feet inside removing the concrete residue.
The safety interlock failed causing the paddles to start moving trapping his left foot resulting in partial amputation.
Reilly Concrete Pumping of St Helens admitted a safety breach and was fined £8,000 with costs of £1746.
Speaking after the hearing Health and Safety inspector Chris Wilcox said: “This tragic accident has left the employee suffering life changing injury.
“Employers are legally required to ensure that work equipment is maintained in a safe condition for use, which in this case was the safety interlock on the hopper grille.”