set off vs touch off

set off and touch off both are verbs.

Word	Noun	Adjective	Verb	Adverb
set off	No	No	Yes	No
touch off	No	No	Yes	No

As verbs, set off and touch off are synonyms defined as:

Other synonyms of set off include activate, actuate, spark, spark off, trigger, trigger off, trip.

set off (verb)	touch off (verb)
cause to burst with a violent release of energy	put in motion or move to act
set in motion or cause to begin
direct attention to, as if by means of contrast
provoke or stir up
put in motion or move to act
depart for someplace
make up for