Engineers are trained to learn from visual content (primarily math and physics with lots of equations). "We (engineers) are accustomed to both quick learning (by looking up a formula) and in-depth learning (understanding how the formula was derived). A video can provide an example of the concept, but will generally not provide fundamental engineering concepts."
True interactivity involves changing behaviors based on the student's response. The simple form of this is to provide the learner with multiple expositions of the same material accessed through links on a page. These expositions could include a step-by-step table, a link to a journal article, a formula derivation, a practical example of the implications of the formula, a quiz, or a tracked test.
In addition every graphic, audio, video, hot-zone, or other non-text element should be carefully scrutinized and justified. "Does it convey new information? Does the student's action relate to the content, or is the student's action simply a display control?"
My recommendation? A good book layout will be most effective for training engineers. An instructionally sound book approach is more than a series of linked slides with a table of contents on the sidebar. Each page of content should include links to sub-pages with different expositions of the same material, since each learner will gain differently from each presentation. The material should be easily accessible, meaning that at any time when the employee is doing his job, he can use the 'course' as reference material to look up the procedure or formula.
If the course is designed as a one-time, linear set of content, you lose this possibility. But if you can put a search engine on your site, and the content is properly searchable, you will create a reusable resource that the engineers will quickly adopt as part of their "library" of knowledge.