It wouldn't really be worthwhile for just one analysis, but if you're preparing many, or need many versions of similar analyses, then why not explore building the HTML and scripts to do it with a web browser. The scripts for collapsible option trees are fairly common, so read the code of a few webpages that use that structure and borrow any ideas that look good to you.
I don't know how to incorporate calculations into the web browser format, however there is some mathematic capability if you want to learn how to write PERL scripts that can receive and process web forms, and spit out the results. Fault trees are inherently arithmetic calculations, so I don't see an obstacle there. Just the learning curve is steep. Also, this way of doing analysis would be very hard to test or cross-check for accuracy, but it would be ideal if you need to expose your executive managers to an instant calculation of the ramifications of certain design changes.
Should you want to delve into it so far, of course...
STF