Knowing what you just told me I feel lucky not to have gotten hurt when I shot the Can next to the Firelighter.
Seriously, the chances of getting the right mixture and ignition timing right are so minute it's probably more likely that you'd be killed by a falling satellite.
The dangers in this scenario are largely physical, not chemical. Hit a deoderant can with a hammer, it won't shatter but crumple, so shrapnel is certainly not an issue. In the unlikely even that the can tears along its middle, there isn't enough pressure to send the halves flying with any significant velocity. Again, you're more likely to be hurt by a projectile ricochet than anything the can will throw at you.
Hand grenades generate tens of thousands of psi within a brittle metal casing and are lethal to within a radius of 5 metres or so. Your humble deoderant can contains a tiny fraction of that pressure in a vessel already made to contain several times the pressure it's at.
In a nutshell, it's not as dangerous as it might initially sound to a concerned parent - though at the same time, I can't blame your dad for being worried.
