I don't believe that liability insurance would cover the type of thing your talking about. You would require errors and ommissions insurance. This type of insurance is very expensive. $6 to $14k a year. Professional Engineers usually carry this type of insurance, because they are liable for the things they sign and stamp. That's why they are one of the most highly sued professions.
If you do your job correctly, there is no liability on your part. But, when something goes wrong, you never know who their going to implicate.
You may not be at fault, but, can you afford all of the legal fees that would be involved taking on a big corporation?
Then on the other hand, if you don't have the insurance, no lawyer on this planet is going to waste time even trying to get money out of you.
you can't get water from a dry well!
Good Luck!!