First what is the source of this quote "In general, a circuit can only be made intrinsically safe if it requires less than 1 Watt of power"...CSA, ANSI, NFPA,UL, NEC?
Depending on your location, canada, USA or Europe there are strict guidelines that dictate the requirements of intrinsic safety. And namely (based on the minimum ignition energy required by the gas present...which is in turn determined by it's concentration) this is the current and voltage seen at the boundary limits of the intrinsic safe barrier.
There are also limits on the cable, and device's capacitance and inductance, b/c in addition to what the 'source' supplies (mentioned above) the apparatus in the intrinsically safe are have limites on how much voltage, current, and therefore power that they are allowed to GENERATE...i think that this quote may be somehow refering to this...but a general quote like this does not make any sense - intrinsic safety depends on the appliataion, these is not one set rule (in CSA anyway) that makes a generalization like this.
If there is anyone familiar with CSA on this thread please drop me a line. I appreciate your comments and help but i'm not looking for a tutorial on intrinsic safey, I'm looking for a product (see beginning of thread).