Residual voltage at lantern when slider at off /zero

Hi all
Like to pick your experienced brains
I am an Am-dram SM and we are in the UK doing "Absurd Person Singular 
Alan Ayckbourn "  There is a point in the play when the female character 
is constantly trying to sincerely commit suicide by various means other 
characters mis-read her actions as her struggling to do something
One action is to climb on the table with a rope (wa****ng line) to attach 
the rope to the light flex in order to hang herself, to accomplish this 
  she removes the lampshade and bulb having already turned off the power 
at the wall switch [There has to be two fittings so that one remains 
"on"] She then ties the rope at the top of the flex and pulls twice and 
it holds However on the third pull it slides down the flex and pulls off 
the bulb holder exposing the bare wires, Someone misunderstanding her 
action thinks she is trying simply to change the bulb and offers to do 
this realising the bare wires he tries to refit a bulb holder but he is 
very poor at doing this and someone comes in and not thinking turns the 
power back "on" so giving the man an electric shock

My question
1) The light fitting needs to originally be operational (How can I 
secure the bulb holder so that it will be sufficiently attatched to 
safely operate correctly and light the bulb BUT loose enough to be 
pulled of easily when she pulls the rope first time after the third pull 
(ie pull 1 + 2 hold, then pull three pulls off bulb holder at one pull)

2)WHAT VOLTAGE WILL THERE BE AT THE  bulb when the LX operator pulls the 
fader to zero  ( Our LX guys very experience amateur operators / 
designers feel the will be virtually no voltage not enough to give a 
shock (we are on DMX system)
I feel it is unsafe, but don't want to cause unrest and loss of 
friend****p and trust not knowing the correct situation first However If 
my theory is correct I will make the safety first decision and over ride 
their ideas

We have a 50v system with 50v bulbs could this be attached to the DMX 
channel as a switch rather than dimmer circuit.

Sorry for long winded question