I'm assuming you just mean checking the left and right side of a block?
The straightforward way.. needs optimizing, but it shows you what you need to do.
+ For y = 0 to array.height - 1
+ For x = 1 to array.width-2
+ if array.at( x-1, y ) = 0
+ if array.at( x, y ) = 1
+ if array.at( x+1, y ) = 0
- set array.at( x, y ) to 0
The 3 IFs are as one event block.