John Marriott, from Scalford, Leicestershire, was delivering a lorry carrying two chemicals to Walkers when he mixed up the transferal hoses, creating toxic chlorine gas.
It was found that Walkers had not trained employees adequately for such a situation and had inadequate evacuation procedures for it.
A spokesman for Walkers' owner PepsiCo said: "The firm was saddened and shocked at the tragic death. The judge noted in his summing up that our employees did everything they could on the day to help Mr Marriott.
"The firm has fully co-operated with the Health and Safety Executive throughout its investigation. We accept the penalty imposed and shall not be appealing the outcome."
A spokeswoman for the Health and Safety Executive (HSE) said: "Lessons have been learned from this. Walkers made improvements straight ßaway: changing delivery to one chemical at a time.
"HSE has reviewed the actions and is content with the changes made."
Marriott's employer Omnichem also pleaded guilty and was fined £150,000 plus costs.