Mortein flea bombs are safe when used according to the instructions. Simple as that. The precautions you take are: remove your animals from the treatment zones. Remove their water and food containers too. Treat the rooms as per the instructions. Leave closed for the recommended time (2hrs I think), then ventilate for an hour before replacing your animals.
I have used this routine in the snake room on the 2 occasions I've encountered mites - remove the snakes and their water bowls, leave enclosures open, set bomb off... etc...etc. Do not wash the enclosures or wipe them over after treatment because you remove the residual hormone growth retardant, thus reucing the effectivness of the treatment.
AS I said, the residue is non-toxic, it's not even a poison - it simply stops arthropods going through the moult cycle and reaching adulthood by inhibiting the growth phases. It will not hurt vertebrates such as cats , dogs and snakes.
We have three house dogs which only get fleas when they contact other dogs (we live remotely), and I have snakes which have on a couple of occasions had mites. To treat fleas effectively, you need to treat the animal AND the environment in which it lives. If you have carpets, the only way you'll control fleas in the long term is by using a product like the Mortein bombs to kill all hatched fleas & larvae, and control those which hatch after treatment, which the bombs will do for 3-6 months.
I have been using these products for 20-odd years with no harmful effects ever.
Jamie