Just for clarity, this is the deactivation procedure that you must follow before removing the airbag.
Remove the ignition key
Switch off all electrical equipment
Disconnect the battery negative and insulate the terminal to prevent any accidental reconnection
Wait at least 3 minutes for the back-up capacitor to dissipate
Do not place your arms or face in front of the airbag whilst disconnecting or removing. Carry the airbag facing away from you, and store the airbag face up. Replace the securing screws with new when refitting.