Question from the plumbing course

I’m going through the plumbing course and came across the following paragraph in regards to having a catch pan under a water heater…

*A relief-valve pipe terminating into a water leak catch pan is not permitted, because the pan is not an indirect waste receptor. Most pans have only a ¾ inch-diameter (19 mm) drain outlet, which is not capable of gravity draining the pressurized discharge of the relief valve at full flow. *

My question here is “What does it matter?” If the TPR discharges and overflows the catch pan, how is that any different than having it discharge directly at the floor? I’m probably missing something very simple or obvious, or maybe I just don’t understand the context of what is going on here, so if someone could explain it a little better for me I would appreciate it.

Mark, a catch pan cannot handle the water flow of a TPR discharge without overflowing and damaging the structure.(think attic)

Got it. Thanks Mike. Knew it had to be simple. Frankly, I almost never see a catch pan under water heaters. They are amost always placed in unfinished basements around here, so it doesn’t come up much.

As they are here Mark.