BPEL (Business Process Execution Language) has become the standard for specifying and executing workflow specifications for web service composition invocation. A major weakness of BPEL is the lack of so-called "human workflow" support. The BPEL4People specification tries to amend this by adding human task support to BPEL. In this paper, we propose a formal model of BPEL4People using the CSP process algebra, and discuss some issues we found through analyzing the model. Although based on BPEL4People, this is a general work, and can also be viewed as a formal model of human workflow.