Source of theatrical effect – risk bringing in railway (3,3)
I believe the answer is:
dry ice
'source of theatrical effect' is the definition.
'dry ice' can be an answer for 'effect' (I have seen 'theatrical effect' mean 'dry ice' so perhaps 'effect' could also mean 'dry ice'). I am not certain of the 'source of theatrical' bit.
'risk bringing in railway' is the wordplay.
'risk' becomes 'dice' (I am not sure about this - if you are sure you should believe this answer much more).
'bringing in' indicates putting letters inside.
'railway' becomes 'ry' (abbreviation for railway).
'dice' placed around 'ry' is 'DRY ICE'.
Can you help me to learn more?
(Other definitions for dry ice that I've seen before include "Carbon dioxide vapour used on stage" , "Solid carbon dioxide (used for a stage effect)" , "Theatrical mist" , "Solidified CO2" , "may be used for effect on stage" .)