Biagio Malacaria died in hospital three weeks after catching fire while draining a vehicle's fuel system at Alexanders of Twickenham, a MOT, service and repair workshop.
Last week the City of London Magistrates Court found Alexanders of Twickenham guilty of failing to ensure the safety at work of its employees.
It fined the company £20,000, the maximum fine possible in a magistrates court for the offence, and orders it to pay costs of £16,905.
HM Inspector of Health and Safety Andrew Withers, who was prosecuting, said: "This is a case where a man died as a result of serious injuries he suffered after working with woefully inadequate equipment, and it is shocking that the employer had not realised the danger created by petrol being moved and stored in open containers near obvious sources of ignition."
"The company failed in its duties in a number of ways including having no risk assessment for fire and explosions, a lack of safety measures for this type of work and failing to ensure that all staff were suitably trained."