We had this happen one whole day but we knew a day in advance. Take a personal electric fan to work with you to train just on you all day and a small cooler bag with an ice bag full of ice from home to put on the back of your neck from time to time then return to the fridge, a cloth to moisten and wash your face, neck, arms and leg with a few times during the day and, most of all, bring a sack of ice from the store with you and guard it closely. All your coworkers will be in it once the office ice supply is done - and it will be exhausted early on so everybody will start to want to use your ice! So guard your ice well
since icy, cold drinks will see you through an 85 degree day with a fan, cold drinks, a cold cloth wash-off a few times a day and the boss letting you go home early! We were let out at 2:30 p.m. and that's the only way we made it. Good luck!