a. bisporus -
I agree with your position that it is never completely safe to activate even a low power vhf or uhf transmitter in an environment of potentially explosive gasses. Cell phones fall in this category, along with walkie talkies.
The possibility of direct arcing in the transmit switch or relay is fairly remote in modern low power devices, but the possibility exists for conductive objects in the vicinity of the antenna to act like a transformer coil which, if it is not your lucky day, can pickup part of the signal, resonate with the transmitted frequency, and thus increase the small signal voltage by a factor of a thousand times or more. The induced high voltage can then arc to an adjacent ground and set off the works with a boom. Somewhat like an automotive spark coil.
'Intrinsically Safe' is an industrial 'term of art' for a design standard known well to those who work in potentially explosive environments such as chemical plants. It refers to wiring methods, mostly for sensors and signal circuits, with low voltages and low currents methodically limited to levels below the minimum threshold for gas ignition. There is no easy way to do that with transmitters operating at power levels typical of hand-held units.