It's very true for most benzos, but flurazepam has a higher toxicity than most. Here is an extract from Wikipedia, found here:
https://en.m.wikipedia.org/wiki/Benzodiazepine_overdose
Flurazepam, now rarely prescribed in the United Kingdom and Australia, had the highest fatal toxicity index of any benzodiazepine (15.0), followed by temazepam (11.9), versus benzodiazepines overall (5.9), taken with or without alcohol.
Here are two case reports:
https://www.ncbi.nlm.nih.gov/pubmed/16501350
https://www.ncbi.nlm.nih.gov/pubmed/533364
But 20 x 30mg certainly wouldn't be enough. When I researched it before, I found that 120 x 30mg and possibly mixed with grapefruit juice (not to be confused with grape juice) and/or Tagamet, though I've forgotten how much grapefruit juice affects flurazepam.
But it's best to do some more research into it.