IATA AHM630 6.7.2 is recommended practice.
AHM 631 gives all the hand signals including fire.
Never ever be connected to an aircraft by a headset during a lightning storm.
No OTP critieria should over-ride the safety of the ground crew.
Stay safe, not fried.
There was a ramp worker killed in S America a few years ago when his equipment tug was struck by lightning and he was fried in his seat. Not pleasant but a good reminder to take your crew off the ramp if lightning is near your airfield.