So then, I am less safe in the garage when the water heater decides to exhale its demon’s breath/spit? As opposed to in my basement where I will likely be in closer quarters to said demons revenge? 
That all depends on where your WH is located, and what you are doing in close proximity to it.
In my 1887 home, the WH is on the opposite side of the utility chimney from the clothes washer and dryer.
It is a very high risk location when someone is doing laundry.
Other than that, it has near zero risk as we only use our basement for storage, so are rarely down their doing other activities.
If these things popped off like a steam whistle, trust me, the manufacturers and guberment officials would be having us route them to a place far away from where anyone would ever be present.
The valve is only going to release small amounts of water (and possibly steam) in 99.9999% of cases, in my opinion. There will be no explosion of scalding water over everything and everyone nearby.
Now, if the valve is malfunctioning, anything is possible, including a tank explosion.
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And there is the primary concern.
Virtually nobody performs annual maintenance on their WH, thus the probability of a defective unit is high.
My WH is nearing 32 years old, and still works as intended.
Due to the risky location, and the units age, the last time the TPRV was replaced (about 7 years ago), I also had a Watts Pressure Valve installed as added insurance. I have never seen a single drop of moisture from either valve, ever. .
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On a separate note, but along the same lines. I had an inspection with the water heater installed in a closet at the center of the home earlier this week. It had a 1/4" TPR drain pipe and it was crimped where they bent it to fit the new water heater. I wrote it up. Days later I received a phone call from the client with the plumber on the phone. The plumbing contractor stated that it wasn’t an issue and didn’t see anyway of doing anything else. I’ve seen 1/2" pipe quite often, but 1/4" was a first and would not have expected to have a “professional” in the field to say it is acceptable especially with the crimp in it.
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Yeah, no… That would be in RED in my report.
Just tell them to watch that myth busters episode of the water heater explosion…
I’m sure if the client asked the plumber to put that in writing, he would have a change of heart.
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All of the TRPV discharges that I’ve experienced have been slow leaks.
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I guess this is kinda what I was wondering - would this be like a total evacuation of the tank or just a quick burst like when you test the valve.
Personally I’d never touch the valve. What is the plan if it doesn’t stop leaking afterwards?
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I mean as a home owner testing the valve not as an inspector. 
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Not for me. I guess it may be in the SOP for some states. But I don’t know.
I used to take a pressure test on the water heater drain valve and quit doing that because about half the time the damn valves would not seal back closed.
I don’t think much is accomplished by pulling on the TPR valve anyway as it does not simulate an actual discharge event.
Sorry I misread your post. I guess as a home owner you can do what you want but I still would bother as it is not testing pressure nor temperature release.
No worries, I wasn’t clear enough.
Learning a bunch. Thanks for all the insights.
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Shut off the WH and replace the TPRV!
Ditto.
Has there ever been a tested valve that hasn’t leaked afterwards?
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There is most likely no other option. I would not be concerned about it.
Yes I misread his post and thought he was talking about fiddling with them as a HI.
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