re: Workshop fire -- averted . . . and a "whuf" question

UPDATE: It was suggested that I could have hit metal. While I didn’t think that was very likely, I still had the sawdust on the floor and decided to filter through it. I found nothing with my fingers, but using my magnet, this is what I discovered:

There are two very tiny metal fragments at the 4 o’clock position. That may very well have been the culprit. The reason for the surprise is that there was nothing on the first three passes. Whatever it was must have been embedded in the manufacturing process.

But I would still like to know what would happen if DC/vac were attached when such an event occurred?

L/W