This is what the 2006 handbook says
To be completely reliable, an emergency supply must function in all emergencies, not just during unexpected interruptions to the normal supply. An emergency supply must deliver power continuously during natural disasters (e.g., storms, floods, fires, and earthquakes) when all community supplies of electricity, water, and fuel are cut off, either accidentally or intentionally. A fuel supply must be available on site. Two or more generator sets, properly interconnected, are more reliable than a single set.
The intention of Rule 24-306 is to ensure that the power supply to a health care facility is as reliable as possible under all operating conditions and that the installation is in compliance with the requirements of CAN/CSA-Z32.
I just wanted to play with my new 2006 CEC CD