The Supreme Court, with judgment no. 9913/16, gave a ruling about damages at work, specifying what exactly is meant by the expression " working circumstance".

How it is considered the accident at work by the law?

It is defined as an injury that occurred “due to violent causes during work, from which is derived the death or permanent disability to work, absolute or partial, or a total/temporary disability that involves abstaining from work for more than three days”. 

A direct connection with work it's not needed, the injury can depend on third parties or their worker's events, though an occasional report between the injury and the work it's necessary. What really matters is the "specific" risk, compared to the one in which anyone else would be exposed.

With this judgement, the Supreme Court confirmed that the "working circumstances" are the conditions (socio-economic, environmental ...) in which work takes place, activities in which it is implied that the worker may suffer harm, and it is not necessary that this damages arises from the apparatus of  production or  third parties etc.: however, the only limit is the so-called "elective risk", that is caused by a voluntary choice of the worker.