Calcium chloride is used extensively in the food industry and is considered a very safe additive by all the food safety bodies. When it comes to pickles it has two primary functions, it gives a salty taste and (more importantly) keeps the pickles crisp. Without calcium chloride your pickles will go soft fairly quickly in the pickling vinegar.
While calcium chloride is safe to eat it is still possible to eat to much which could lead to a condition called hypercalcemia. You would have to be going some to manage this though, it would be unbelievably salty and apparetly bitter. As such it’s important to control how much you add to pickles.
I’ve found it exceedingly difficult to find an authoritative source for how much can be added. This source suggests Canada recommends 0.4% w/v maximum but apparently 1.5g per litre is usually ample. This source recommends 0.2% w/v and says the FDA has a limit of 0.3% w/v.
After much searching I came across this paper which suggests the optimal level for pickled peppers is 0.2% w/v
What is w/v?
This means weight of solid in volume of solute. So for example a 0.2% w/v solution of calcium chloride in vinegar would be 2g/litre (e.g. 2/1000=0.2)
Weighing such a small amount accurately will be difficult on kitchen scales. I will weight out a much greater quality, probably 32g, and then repeatedly divide it in two until I have a pile that will weight approximately 2g. e.g. 32/2 –> 16, 16/2–> 8, 8/2 –> 4, 4/2 –> 2. This trick is necessary to get away from the dead zone most scales have at the start, they typically won’t weight under 5 or 10g. Dividing by eye is really quite accurate.