Most corporate SOCs would probably investigate IRC connections at least briefly, they have a very high signal to noise ratio for compromised devices. Modern security devices do generate a tremendous amount of information, but the security operations industry as a whole and SIEMs in particular were developed to make it feasible to risk score and triage these findings.

A well-configured corporate firewall is going to block anything that looks like an IRC packet, because for the overwhelming majority of users, the probability of that packet being malicious is ~1.