True, and because you don't flood the pcb with it and that it evaporates fast, risk is minimised. You only need to apply to the parts that you think are suspect in a very small area at a time. Because you use a current limited supply you know that dangerous currents and therefore sufficient to allow tants for example to combust isn't possible so ignition is not likely. The faulty part will be warmer then others in the area and so the evaporation will be more visible on that part. Also because the PSU has current limiting, as soon as it reaches the faulty part the voltage drops to virtually zero but the current still flows thus the localised heating affect above the ambient will still occur.
If it was half as dangerous as has been suggested then why do so many people do it on a regular basis without incidents? Like handling electricity you need to take care and not limiting the current is asking for trouble, so one has to be sensible as always.
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I was joking but squirting flammable liquids on a live PCB does sound like a risk. You may not burn down your house every time, but it'd definitely be a hard one to explain to your insurer when you do.
Isn't everything a risk? But who in their right mind would squirt flammable liquid onto a live PCB? I'd hardly call a PCB, removed from the equipment, in a well ventilated room with just a single supply rail connected but switched off, PSU set to a low current, and as everyone knows a decent bench power supply when set in constant current mode, will when connected onto a short circuit cause the voltage to drop almost zero so there is extremely little energy to create a spark.
I don't see how a PCB thus connected could be honestly considered to be "live", there is absolutely zero chance of the PCB operating normally under such test conditions as it is starved of the other supply rails and also of the energy it would normally consume.
This is the basic concept of how intrinsically safe equipment operates in areas of extremely high risk of explosion as a result of overheating and or a spark, it does so be keeping the voltage low and current low as well and it is interesting to note that the following link
https://www.omega.co.uk/technical-learning/understanding-what-is-meant-by-intrinsically-safe.html it states the voltage is generally kept below 29v and the current below 300mA by protection devices and in general most such equipment would typically be rated at 24v and a simpler way would to think of it would be to keep the power below 1.3W.
Here is an extract from that linkHow Does Intrinsic Safety Equipment Work?
Avoiding ignition entails minimizing both the available power and the maximum temperatures. Defining the maximum level of available power is complex, but in general terms can be considered as meaning voltage less than 29V and under 300 mA. A simpler view is to say that power must be less than 1.3 W. (Note that much instrumentation requires 24V and can often be designed to draw less than 500 mA; sufficient to meet IS certification in many situations)
So in real terms, providing people take sensible precautions and use decent equipment and do not squirt the liquid onto a live PCB then they should be OK. The method is that you have the PCB switched off, pour a little liquid around the part you suspect of having the short (the key here is a little, just like using flux, just enough for the part in question) and switching the power on and watching to see the part dries out before the residue liquid around it, if so then it signifies that the part is getting hotter the the parts/area around it and is more then likely to be your faulty part.
This technique is especially useful on PCB's stuffed full of SMD devices as was demonstrated in the video examples given where it is less easy to disconnect a leg for testing in the normal fashion, especially on items such as chips.
Fluke for instance actually make handheld DMM's for testing purposes within such environments for working on equipment to carry out vital repairs etc.
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