Having worked in the industry..most standby generators in commercial applications only have a fuel supply for a temporary power outage. Once it gets to be three days to a week, they need resupply. Most of the time diesel generators don’t fail..they either run out of fuel..or have flat batteries when they are supposed to start. Many building codes and zoning laws just don’t let them keep enough fuel on site.
I have a 100 gallon propane tank for my 15KW generator. That usually lasts for 48 hours.
Power outages with Irene and the "halloween snow" of 2011 were just under 48 hours.
Only 5 hours 15 minutes with Sandy.