Why should transformer oil not be used as diesel fuel?

Transformer oil is not formulated for combustion and may contain additives or degradation byproducts that produce toxic emissions. Using it as diesel fuel poses serious environmental, health, and legal risks. In many jurisdictions, transformer oil is classified as regulated waste, especially if PCB contamination is possible. Burning it can release hazardous compounds and violate environmental regulations. Proper recycling or disposal through licensed facilities is required instead of fuel use.