It would be nice if they could grit the whole area, good employee relations and all that, but even so they cant be entirely responsible for the weather. Otherwise they would have to make sure they cleared every single inch of the yard of rain, ice or hail. They could clear it for example, and the temperatures drop and it freezes again.
H&S would suggest you assess the risk and if its really really bad ask them either to clear it or to issue you with some ice grips for your shoes. Stay safe.