Certain forms of fluoride and bromide, such as sulfuryl fluoride exposure MUST be pretreated with calcium PRIOR to lethal dosing... animals pretreated with calcium supplementation in trials survive lethal dosing...
POST treatment with calcium DOES NOT ENSURE SURVIVABILITY, dependent upon rate of exposure.
Now that does not mean one should go out and megadose on CALCIUM... adequate daily absorbable intake should be fine for most people, UNLESS, there is a known deficiency.