Usually a salad bar (or saladette) will contain a number of protein ingredients such as tuna, eggs, meats, coleslaw (mayonnaise). Often the containers used to display the salads are not tight fitting in the chiller unit so the unit loses a lot of cold air. This in turn can allow dense protein items to rise in temperature.
The rule is to check the temperature of any protein items after service (or a maximum of 4 hours) then discard if the temperature has 
risen over 8°C.
Alert – Always check the food temperature as the chiller readout will only tell you the air temperature
And remember – Knowledge is knowing a tomato is a fruit: wisdom is not putting it in a fruit salad!
Weekly Food Fact – Did you know that the inventor of HP Sauce Frederick Gibson Garton named it after he heard it was being served in a restaurant in the Houses of parliament (HP). The label still carries a picture of the building