First and foremost - relax. Of course, this is easier said than done but the fact that you already have a job within the company will work very much in your favour.
Second - prepare yourself as much as you possibly can by thinking of the types of questions they might ask you and formulating your answers ahead of time. What were the responsibilities of the previous shop foreman? How do you think you could improve on what he/she was doing? Coming from a non-management position, what ideas or observations do you have as to how the operation could be made safer and more efficient? Even if these aren't the questions they ask you, it will help you to solidify a train of thought in your mind and churn up all of those things that you may have forgotten about from long ago that will help to make you look like the concerned and responsible employee that you are. The better prepared you are, the more confident and relaxed you will be in the interview.
Third - have a list of questions prepared. Having some thoughful questions of your own ready to ask will show that you're interested in learning and becoming a better asset to the company. Nobody expects you to know everything, but they do expect to see that as you move into management you have the capacity to look beyond the obvious, everyday issues and keep the bigger picture in mind.
Best of luck to you!