A quote from IEEE 1584 - 2002 (4.6) should answer your questions about what and how fuse time-current characteristics are used for determining the duration of the arcs:
Quote:
For fuses, the manufacturer’s time-current curves may include both melting and clearing time. If so, use the clearing time. If they show only the average melt time, add to that time 15%, up to 0.03 seconds, and 10% above 0.03 seconds to determine total clearing time. If the arcing fault current is above the total clearing time at the bottom of the curve (0.01 seconds), use 0.01 seconds for the time.
Typically, fuse time-current characteristics tolerance is +/- 5%. I believe the curve tolerance has been factored in into above recommendation. I would research the web or contact fuse manufacturers or service providers like SKM to find old / discontinued fuse data.
Most arc flash software come with built in protection device libraries. Some of them also allow end user to add more fuses and breakers in case they are not already listed in the supplied libraries. As an example, please find below a screen shot from iAFA V1.0 mobile app showing old Brush 500MT fuse and GE F 225 Line 250A molded-case breaker information and characteristics being added to the program protection library:
The program would than determine arc duration based on selected protection device characteristics and predicted arcing current. You can download your free copy of iAFA V1.0 online at
http://www.arcadvisor.com/arcflash/iafa.html