A method for preventing unsafe transmission on an incompatible network with a multi-protocol intrinsically safe handheld field maintenance tool as provided. The method preferably includes checking voltage levels on two sets of network connections when a network connection is detected or indicated on one set. If incompatible voltage levels are detected, the field technician is warned. If voltage levels are appropriate on a selected set of network terminals, the method continues by listening for network traffic of the selected network type. In this manner, a multi-protocol intrinsically safe handheld field maintenance tool is operable with multiple process control communication protocols while minimizing the risk of incompatible data/signal transmission upon process communication loops.