1994 Chevy Truck spark plug blew out porcelain while runnin

did the plug blow out of the hole/

check to see if the bridge of the spark plug is bent or the plug is damaged, such as being struck by a piston.

if no damage is noted chances are the porcelain was poor, dropped and then later it cracked due to normal operating conditions.

To add a few others I have seen a few plugs with very poor crimps to retain the porcelain and even a couple that were not crimped at all!

very possible as swilliams says.

basically just check to see if the porcelain is still in the plugs, if theres no porcelain at all probably a poor crimp.