Engineering group Pressure Technologies has been found guilty following a fatal accident at its subsidiary Chesterfield Special Cylinders in June 2015.
The trial, which started earlier this month and was held at Sheffield Crown Court, was brought forward by the Health & Safety Executive.
Sheffield-based Pressure Technologies said trial proceedings have concluded and the jury delivered a guilty verdict pursuant to Section 2 of the Health and Safety at Work Act 1974.
A sentencing hearing has been scheduled for December 9 and the company expects its penalty will be determined on this date.
The group had previously submitted a plea of not guilty on March 6 to a charge brought by HSE pursuant to the Health and Safety at Work Act 1974.
In March the firm issued a statement saying: "The company emphatically denies the charge brought by HSE and will deliver a strong defence."