I am always impressed with the speed of those things. One time the edge of a hot pan burned through the insulation to another kitchen appliance, and ended up contacting the live wire. The stove was electric, so the elements were grounded and so the metal pan was too. Sparks fly, definitely more than enough current to trip the 15A breaker serving that circuit, but the GFCI tripped before the breaker could even react, super crazy fast. I heard somewhere that if you touch the live wire on a modern-day GFCI receptacle you might not even have time to feel the shock before it disconnects, but that seems like an exaggeration. Also, RCDs in Europe need like 30mA to trip, which I think is just crazy. You would probably be long sizzled or fibrillated(?) by then.

The more sensitive GFCI's use to gave two triggers (similar to how circuit breakers respond to an overcurrent): The sensitive one, with quite some phase sensitive discrimination (to not respond to capacitive currents, as these come from EMC filters and not faults) so acting with some delay, plus a fast one, responding to any imbalance greater than about 30..100mA, but really instantly (often a direct electromagnet powered from the current transformer by the imbalance itself), designed to act on these hard shorts, so mainly prevent fires (light touching may not trip a higher current overcurrent breaker in time).

Only had one RCD incident that took a while to find, partly because I was overlooking the obvious 🤣, got a phone call from the wife one afternoon at work, “all the electric has gone off”!
Long story short, I talked her through unplugging items one by one until the RCD reset, the fridge being the offending item.
When I got home I looked at all the motor wiring, start capacitor, and connections and found nothing, plugged it back in, RCD went again!
What I was overlooking was the inside of the fridge, and the problem?, the door hadn’t properly been shut and it defrosted slightly getting the coolness setting switch damp!
Dried the wires off behind the switch and it was problem free again 🥳, if only I had checked that first!

I guess you may say your fridge has been saved by the GFCI - even when AC moves the ions back and forth, once detached by one halfwave, the second half never returns them back, so the metals do corrode heavilly when wet and exposed to electrolytic currents...

Sorry to swerve off topic, but how did you change the font of your message?

Also, RCDs in Europe need like 30mA to trip, which I think is just crazy. You would probably be long sizzled or fibrillated(?) by then.

In Europe and around, with higher line voltage, capacitive leaks are higher, too. Practice shows that with real home appliace loads 10mA RCDs generate too many nuisance trips, so 30mA rating is popular. Even if lifesaving abilities are somewhat reduced. Still with proper grounding, using RCD helps to detect short circuit at much earlier stage than grounding alone.

I think "we" are only using the 30mA GFCI because it originated as a whole house protection system. Starting out as 500 or 300mA around the 1960s, where the assumption was that any leak you could expect would be large enough to trip that. It was not touch safety, but more fire safety if it was a strong leak but not a hard short circuit that could blow the fuse. 
Moving onto 30mA in the 70s somewhere. 30mA is the guaranteed trip level, with many 30mA GFCIs already tripping in the low 20s. For a long time 30mA has been seen as the hard cut off for where AC gets truly life dangerous, so 30mA was chosen as a compromise between nuisance trips (Remember, it is 1 GFCI for an entire house) and safety. Back then it was not unusual for a washing machine or a dishwasher to have some leakage, so they couldn't go too low with that.
In my parents' 1970s house, the washing machine even had its own circuit (while the rest of the house, divided up in 3 or 4 16a circuits, were behind one 30mA GFCI), explicitely without GFCI because that was acceptable in the 70s because of nuisance trips. After a renovation this of course was also put behind a GFCI, and with the modern washers it has never tripped so far.

It was not until a bit later that having more than 1 GFCI for the entire house became more commonplace. My 1 bedroom apartment has 2 30mA GFCIs (+ one combined GFCI + 16a breaker for the PV system). With modern 'wet devices' being pretty low leakage and them being divided over multiple GFCI circuits, i now see opportunity to lower the sensitivity of the now partial-house GFCIs to a level where they reduce the risk of death when getting shocked even more. But code moves slowly, so at the moment even if you have 9 circuits with 3 GFCIs, 30mA units are still being installed.

One common exception, however, is above ground inflatable pools/jacuzzis. Those often come with an in-line GFCI with a much lower trigger current. I do not know if that's code by now, or whether it's just sensible design by the folks who engineer those things. 

30mA won't kill you. You will feel it, but it will need a lot of time...
Plus the 230V has another advantage: The fault currents do not tend to stay low, they do increase a lot within few seconds. And with that it becomes enough to trip the protector. So yes, up to 30mA would be way too high to flow unchecked, in real life even way smaller current becomes more than 30mA in seconds and trip it, so you are not exposed more than these few seconds. The time is the key factor here.
Yes, there are more sensitive devices, but there is a catch: These are line voltage dependent protectors. So they are not able to disconnect unless the mains voltage supply is present on their input. So if a fault is upstream  (e.g. a broken neutral), the mains dependent protection is not able to trip, so it leaves the circuit unprotected.
The 30mA is just the minimum which you may reach where the device trips on the fault current imbalance itself, without the need to have the mains voltage present, so to sustain the protection function even with e.g. the Neutral fault.

The problem is not that much the current itself, but the ability of the trigger system to discriminate between a real fault vs a normal capacitive leakage, when the capacitive leakage current becomes too close and mainly in the HF events (like a nearby thunderstorm, some other faults happening in another branches, high power switching transients,...) it can become above the 10..15mA and so cause nuisance tripping.
So for lower currents sensitivities you need to use filtering/phase matching discrimination, which at first are functions that need power supply (so the mains present) and second needs to see the mains voltage itself to have a phase reference. So can not work without the mains presence.

So all the above means the 30mA became a kind of optimum: Sufficiently sensitive to protect people, yet to not nuisance trip and cause hazards and damages from unnecessary power cutouts.

So I have a bit of a funny story to tell relating to GFCIs.

Basically, when my physics teacher was building an addition to his home, he only later decided he wanted a fan in the middle of his room (after installing the sheet rock, spackling, and putting in can lights). So, what he wound up doing was going the lazy route. Being that his kid was only 5 or 6 at the time, all outlets within a child's reach were GFCIs with "kid-proof" covers. Essentially what he did was mount a fan on the ceiling, run wiring across the ceiling and down the wall, and plugged the fan into the GFCI. He obviously covered the ugly wire with a sheathe, etc. But what he wound up finding is that the rotation of the fan blades (and thus inherently, the motor) after shutting the fan off with the remote led to an imbalanced "back current" being sent back through the GFCI. Supposedly, the reason why the spinning fan blades tripped the GFCI was because they generated a "back EMF" [can someone please explain this terminology to me], which the GFCI interpreted as a ground fault.

@Maxim

All GFCIs in the room? Was this before tamper-resistant receptacles? GFCIs are expensive!

This is definitely possible, as you know, disconnecting an inductive load creates a voltage pulse, called a flyback pulse. If only one leg is being disconnected when the fan turns off (usually the hot wire and not the neutral wire), that flyback could create a small momentary current between neutral and ground due to the capacitive coupling between the windings (connected to only neutral when the fan is off) and the iron core (connected to ground). I suppose that flyback in combination with the capacitive coupling was able to generate a pulse of current over 5mA, so it tripped the GFCI. I could be wrong, but I think this is the most likely explanation.

Sorry to swerve off topic, but how did you change the font of your message?

On the same line as the bold and underline buttons, there is also a "font face" drop-down menu where you can select from various fonts.

Only had one RCD incident that took a while to find, partly because I was overlooking the obvious 🤣, got a phone call from the wife one afternoon at work, “all the electric has gone off”!
Long story short, I talked her through unplugging items one by one until the RCD reset, the fridge being the offending item.
When I got home I looked at all the motor wiring, start capacitor, and connections and found nothing, plugged it back in, RCD went again!
What I was overlooking was the inside of the fridge, and the problem?, the door hadn’t properly been shut and it defrosted slightly getting the coolness setting switch damp!
Dried the wires off behind the switch and it was problem free again 🥳, if only I had checked that first!

Very interesting... Almost seems very slightly similar to my experience with the toaster in that something was conducting through a path of moisture.  That would certainly be aggravating.  I must say, I've found it peculiar that only ONE RCD protects the entire house; it seems like it would be a terrible nuisance if it decided to randomly (or unexpectedly) trip!