Results from another test I read some time back indicated that the primers were actually more dangerous than the bullets when loose ammunition catches on fire. The primers can eject at extremely high velocity--going fast enough to be dangerous. However, they are so light that they can be stopped easily. Typical firefighting protective gear is sufficient to prevent injury.
The real safety concern is loaded firearms. When the temperature reaches the flashpoint of the powder/primer, chambered rounds will be fired normally and, of course, the fired bullet has the potential to cause lethal wounds.