View Full Version : Radhaz and Avgas

Agaricus bisporus
19th Jul 2002, 02:51
Sitution; during overwing refuelling light piston a/c with avgas.

Problem; fueller was holding his 2 way radio in the same hand as the refuelling nozzle and was about to reply to it by leaning towards it and keying the TX with his other hand, the radio and the avgas nozzle being within about three inches of each other.

I asked him not to, he got stroppy, I inisted; he thankfully desisted but assured me his boss had said that this particular radio was OK in this situation whch frankly I do not believe.

His fuel bowser had a prominent sign in the front windscreen saying "No Naked Lights, No Flash Photos, No Radios".

Nonetheles the common practice on this airfield is clearly for fuellers to routinely use (admtedly low wattage) Motorola walkie talkie radios .

Is there such a thing as any radio transmitter that is safe within inches of an aircraft fuel nozzle?

19th Jul 2002, 08:35
Not to my knowledge!

In addition to the RF hazard (which may indeed be small), there is the possibility of sparks from bad transmitter switches, etc. On a hot day especially, you don't need any more risks while fueling!

Red Four
19th Jul 2002, 22:34
I would guess that his radio was an 'intrinsically safe' and had been cleared for use in such situations.

20th Jul 2002, 03:14
I would guess not...

How many such "intrinsically safe" radios exist? Who certifies them as such? How much do they cost, compared with "normal" radios?

Remember, we're talking not only about RF radiation that would pose a problem for radio-controlled blasting caps, etc. nearby, but transmitting from within a potentially explosive atmosphere...

20th Jul 2002, 19:32
Oz rules specify (used to specify?) that no electrical switches/devices are to be operated during refueling operations. Excluding those pertinent to refuelling, of course.

Just keying the mic. is operating a switch.

21st Jul 2002, 01:46
Watch what you wear, too. In cold, dry weather a nylon jacket can create enough static electricity to ignite gas fumes. Know of a Norseman that caught fire that way.

21st Jul 2002, 09:06
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.