The PFD depicts the process route, showing the elements that make up a business function. It therefore

• defines the role/task and operating conditions of each section or unit in the process line
• gives an overall view of the process route
• allows an insight into the overall operability of the process
• provides an initial assessment of potential sources of hazards

There are usually two stages to developing the PFD, namely the

• operational specification and the
• functional specification

Here, you decide upon the sections of the process that would be needed to produce revenue. In most cases, the required sections would have been dictated by the chosen means of doing business. The result at this stage is the process flowsheet.

Next, using process knowledge together with information obtained about individual processes, you will have to provide details about the kind and number of main process units that are required to perform the business function