While human error has long been recognized as a contributor to process incidents, Process Hazard Analysis (PHA) teams often struggle to agree on the frequency at which human errors might occur. This difficulty in reaching a consensus can be due to the varied backgrounds and experiences of team members, as well as the degree to which they believe human error is inevitable as opposed to simply being a reason for discipline. A process that combines research-based, quantitative estimates of human error rates with plant experience and intuition is proposed for use during qualitative PHAs. Use of these quantitative estimates within a qualitative PHA is described, along with one facility's successful implementation of this process. © 2007 American Institute of Chemical Engineers Process Saf Prog, 2007.