Greenstripe Ltd was prosecuted by the Health and Safety Executive (HSE) after an investigation found the employee had been given petrol to burn the waste vegetation.
Warrington Crown Court heard the 31-year-old from Poland, who has asked not to be named, had been working with the company’s operations manager in July 2013 to clear grass and giant hogweed from scrubland on Parkgate Road in Chester.
They returned to the site a few days later, on 2 August, when the employee was told to pour petrol from a can on the pile of waste hogweed before using a cigarette lighter to set it on fire.
As he did this, there was an explosion and he was thrown to the ground. The worker’s face, throat, body, arms and hands were burnt.
The court was told there was no need for the hogweed to be burnt as it could have been taken to a licensed waste site. However, the company had failed to carry out a risk assessment for the work.
Greenstripe Ltd, of Deeside Lane in Sealand, Chester, was fined £23,000 and ordered to pay £9,682 in prosecution costs after pleading guilty to a breach of the Health and Safety at Work etc Act 1974.
Speaking after the hearing, HSE Inspector Deborah Walker said: "A worker has suffered burns that may affect him for the rest of his life because his employer failed to ensure his safety.
"He should never have been told to pour petrol over the weeds and then to light them but Greenstripe didn’t consider that this practice might be dangerous.
"There was absolutely no need for the vegetation to be disposed of in this way, putting the lives of workers in danger. It could easily have been taken to a nearby waste site without the risk of employees being injured."
Information on managing the risks from fires and explosions is available at www.hse.gov.uk/fireandexplosion.