I have been designing, troubleshooting and commissioning process plants since 1991. This is the area I write about.
I write the first draft of my books quickly, straight off the top of my head, based on my personal experience. I then have the draft reviewed in parts by large numbers of other practicing engineers to ensure that it is complete, current and correct.
I then review the reviews, and the sources they suggest, amend and add to the text and then start to bring the text together into a unified whole. Repeated review, rewriting, refining and proof reading takes up far more time than the initial writing stage.
My books are therefore based largely on my own experience and that of the hundreds of other practising engineers who contribute to and review the texts. They are intended to assist others with the process of making engineering education fit for purpose, and to show those wishing to become engineers what practicing engineers think engineering is really about.
I'm in the process of updating all of my books after getting the right back from Elsevier. It looks like they are still printing some copies, but over time, Amazon will have new Amazon KDP editions of all of my books. As of now they only have my dictionary of chemical engineering, an they have not liked the new edition with the old. The new edition without Elsevier markup is way cheaper!
You can also get electronic copies of earlier editions of all of my books direct from me and heavily discounted at leanpub