Alternative is not to work of course.
Not saying the following is ethical or not but remember reading this on here last winter ..... if you alter the surface of the floor with salt then your admiting liability in the event of a claim .. if no salt used then difficult for anyone to prove it was your water that froze ..... so personally I prefer not to work in this temperture ... take today for example it may reach zero or +1 by midday, at 2pm it will start dropping again and possibly by 3pm it will be freezing any water ive left that hasnt evaporated so taking today off as I wont use salt ... IMHO if u need to salt then maybe best to take day off ??