I was driving home from work when my fan blade parted company with the hub. I had installed a Moss 6-blade metal fan on my BJ8 on 3 May 1995 (31,590 miles showing on the odometer). On 16 January 1996 (34,103 miles), there was a sudden and severe vibration. I switched the engine off to investigate. I found a blade had failed and put a 2-inch gash in the radiator header tank. Perhaps the reason that it didn't go through the bonnet was my home-made radiator shroud riveted and screwed to the radiator fan guard and riveted to the side frame of the radiator. The blade knocked the fan guard off the tank, but the shroud remained attached at the sides of the radiator. I had to cut the fan belt to drive the remaining couple of miles home. On further investigation, I found TWO blades missing, not just one. I found the other blade the next day on the ground where I had stopped. I noted that the Moss fan was stamped "made in China".
There was a semicircular cutout at the root of each blade where the two blades had broken off. There were paint chips in some of the other blade cutouts. The blades were not riveted to the hub at all, but were an integral part of the hub.
There was a materials lab where I worked. The lab analyzed the broken blade surfaces and pronounced fatigue failure as the cause.
Moss replaced the fan belt, radiator, and fan (with another identical one). After installing the second fan on 5 March 1996 (34,105 miles), I drove the car to 14 February 1997 (35,660 miles). At that point, I received a bulletin from Moss that instructed anyone who bought such a fan remove it immediately and return it to them for replacement with a different type of fan plus a gift certificate (for $100, as I recall). I did this (and noted that the second fan had paint chips in all the semicircular cutouts, indicating flexing of the blades and probable future failure). This time Moss sent a multi-blade metal fan with stainless steel blades and of a riveted construction. I installed that fan, but it had an objectionable whine. I replaced it because of the noise with a Texas Kooler plastic fan, which remains on the car.
The fan that failed on my car was similar, but not identical to the one Bill Young shows in his photo, which has riveted blades and no semicircular cutouts.