I read in sci.electronics.design that Jeff Liebermann
wrote (in mppp50ho4dr08ahkb3dlbqkcfkp0ih
) about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk