The most common and most likely answer to this crossword clue is the 12 letter word OBSTRUCTIONS
I've seen this crossword clue in The Daily Telegraph
O
B
S
T
R
U
C
T
I
O
N
S
Buddy explains!

The straight part
We know that "barriers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case barriers = obstructions.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OBSTRUCTIONS mean?
OBSTRUCTIONS noun- The act of obstructing, or state of being obstructed.
- Something which obstructs or impedes, either intentionally or unintentionally
- The condition of having the natural powers obstructed in their usual course; the arrest of the vital functions; death.