Have you ever been in a state of concentration where the rest of the world seems to fade away and you are much more productive?
This state is called the Zone.
It is quite well-known in computer circles, but if you work with people who deal with a lot of detail working by themselves–thinking for their livings–you might well be dealing with people who get into the Zone.
Being in the Zone is rather delicate.
We do not like being interrupted while in the Zone. Interrupting someone in the Zone destroys productivity. Think of it as mentally tripping somone.
If you were running across a field and someone tripped you, you would not just lose the time running but also the time of slowing, falling, getting up, brushing off gravel, making sure you were uninjured, and getting back up to speed. It is similar when you interrupt someone in the Zone.
Mind you, you are quite within your rights to insist that people you deal with communicate from time to time. If you have an non-emergency matter, the best way to notify might be to leave a written message or send an E-mail. If you think it is an emergency, try the acid test of whether the person you are interrupting will agree that it is one. If not, do not. If so, interrupt.
Not interrupting also saves a lot of time of people who are not in the Zone and makes for a generally more productive environment. Try it.