Somebody with knowledge of ballistics will probably be able to answer this.
If a suicide bomber in a train detonates an explosive device blowing himself up and a pound coin in his pocket flies out at high speed then hits the floor of the train:
1. Approximately how large a hole will it create?
2. Will the edges of the metal around the hole be pushed upwards similar to that described by eye witnessed on the underground trains following the explosions?
I was discussing the issue with a former Royal Marine who claimed that the holes in the floors of the underground trains following the explosions were caused by hard shrapnel - including coins and keys carried by the bombers and other passengers - flying out from the explosions. This explains why the holes were at a distance from the seats of the explosions and why some passengers close to the seat of the explosion survived and others further away were killed.
How much truth is there to this claim? The former Royal Marine is generally supportive of the official narrative (although he hasn’t read it!) and he discredits any possibilities that the explosions were caused by power surges or explosive devices underneath the trains.