Considering the steps of receiving raw peanuts through the process of mixing of ingredients, we recognize four potential hazards in receiving – one biological, two chemical, and one physical.
The potential biological hazard is Salmonella bacteria.
How do we know this? The scientific literature shows that raw peanuts have had a history of contamination with Salmonella. Many crops grown in the ground have the potential for contamination from the environment or harvesting.
Does Salmonella require a preventive control? Again, when we consider research into the likelihood that people who consume the bacteria will get sick, we decide that a preventative control is necessary. Next, we document the justification in saying Salmonella is a hazard and requires control.
Then, we determine that the process control of roasting could be used to reduce Salmonella to safe levels, but that action would be implemented at a later step.
Now let’s look at that roasting step. We see two potential hazards: the biological Salmonella hazard and a physical hazard of foreign materials. Salmonella does require a preventive control because the bacteria may pose a significant health risk. This is a process control step since the thermal treatment destroys Salmonella. We decide that foreign material does not require a preventive control because we have data from metal detectors that metal rarely shows up in the roasting process. We justify the decision by pointing to preventive maintenance.
Studying the other steps in this example will give you a good feel for what is effective for a hazard analysis. It will take some experience and use of resources to become proficient at identifying hazards, preventive controls, and justifications.