No Broomstick they are not chained down, neither do the chocks touch the wheels. Parking brake only is all that stops them !
IF the 340 is the same as other Airbus' from what I remember the park brake is a lower pressure than the foot brakes. When carrying out high power engine runs one person has to stand on the pegs for the duration.
"There for the grace of......"
Edited to say.. Must type faster, you beat me to it Fargoo.