If you're worried about your boss finding out that you're chatting on IRC using the computer system that belongs to the business and (possibly) during business hours, then you shouldn't be using mIRC in that situation.
There have been a number of times when people have asked for ways to use IRC at work and/or school, looking for ways to get around the blocks that the workplace or school has placed, and we don't help with that.
Now, while I understand that this is not the same thing, it's still a matter of you using IRC at a location where someone else of authority might not be agreeable to you using it. (In this case, your boss).
Even if a "panic" switch was implemented, there's still going to be some delay using it.
What you could do (if it's just sounds you're worried about), is uncheck the Sounds option and leave it unchecked.
