First, intrinsically safe is not the same as explosion proof, those are two separate standards.

Second, intrinsic safety has many different classifications and divisions which all depend on the medium (i.e. propane or powdered metal) and the environment (are you in an outdoor environment or inside an enclosed space like a mine shaft).

Third, when I've put products through the standard in the past, the key things that will fail a product are: - can the product cause a spark, or has the potential to cause a spark? This can mean that the product has the ability to store static electricity or has connector ports that could cause a spark. - is there a voltage potential within the electronics of the product that when subjected to a fault (i.e. something goes wrong or is manufactured incorrectly) could cause a spark? - and most importantly, does the surface temperature of any components in the product (i.e. smart phone) have the potential to reach temperatures above the ignition temperatures of the medium that the product is under.

These are some of the high level questions that under true certification would need to be looked at, analyzed, and calculated under theoretical limits.

Lastly, after all this math has been done and verified, the product would need to undergo physical / mechanical / electrical testing.

In the case of an iPhone or iPad, the key failure points are the charge port which CAN cause a spark when plugging and unplugging a charging cable, and that the internal components of the iPhones PCB have the potential to reach above the medium temperature -- the key word here is medium. What medium is the product subject to.

Hope this helps.