Do you have a copy of the firm's annual report? If it is one with lots of employee pictures, you might get some more clues there. You should have the report for background reading on the company anyway. Even to help recognize some of the faces you will be meeting. Local library?

To generalize, engineers tend to be the more casual dressers in the corporate world, although not quite so casual as computer types. However, middle management and up can still be as formal as any other company.

Romelle