Eg: IPhone SE is said to be water resistant only upto 30 minutes and 1m depth. When something is water resistant, shouldn’t it be resistant irrespective of how long its soaked? What happens post the time limit or depth?
In: Engineering
Depth translates into water pressure. At some pressure the seals will always fail and the water will push past the seals. 30 minutes and 1 meter depth means that they don’t have to design in super expensive seals. The deeper you design for, the more expensive your design comes, because you have to guarantee a higher pressure on the seal, and usually bigger seals.
Water resistant and water proof are actually defined standards in manufacturing.
So while conversationally you may use the terms interchangeably, they actually mean specific things to manufacturers.
Water resistance means it will resist water entering the cavity up to certain tolerances.
Waterproof means that water will not enter at all.
A good way to think about this is a submarine.
If you build a sub, you would likely want to aim for Waterproof right?
What about if the sub is 100ft deep? What about 1000ft deep? What about 10000ft deep.
Each of those depths creates vastly different levels of stress on the sub.
It may be easy to design a sub to withstand the forces at 100ft, but that same design and materials are not likely to stand up to 10000ft.
So a manufacturer you need to understand the use case of your system. In the case of a phone, most manufacturers assume that you are not very likely to check TikTok while drowning in 10+ft of water.
So they engineer phones to survive occasional minor water encounters rather than prolonged exposure or expected operations at depth.
It’s possible that there is other considerations but it’s certainly the case that many mechanical seals will only be rated to certain pressures and time exposures. For example, a thin o ring might be totally waterproof until it reaches a depth of 5 metres where the water pressure will overcome the mechanical force of the o ring. The rating is a combination of these probably cut in half so that the manufacturer can account for sub standard parts or processes.
There is an international standard for testing water resistance.
The parameters given reflect the test that the device was able to pass. No doubt, Apple considered subjecting the device to more stringent tests, and presumably didn’t think that it would pass reliably.
If you exceed the parameters of the test, “nobody knows” (which means “nobody is willing to guarantee”) what might happen. It might be fine, it might get water inside. Regardless, you exceeded the listed water resistance, so if something bad happens it’s “your fault” and Apple doesn’t have to fix it under warrantee.
In that amount of time, the sealants may dissolve. At greater depths, the pressure would overcome the resistance of said seals, and water would push in to anywhere it would fit.
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