Space Engineer's wiki suggests that Small Thruster on a Small Ship destroys an area of 3x3x4 (width, height, depth) behind the exhaust, assuming the space is completely enclosed and filled. A small thruster is capable of dealing damage of up to 5 blocks depth over open space.
However, the wiki doesn't specify whether large thrusters work the same way, and damage the same area. Since a large block is 5x5x5 of a small block, it's reasonable to assume a destruction zone of 15x15x20.
Does anyone know for sure if the destruction zone works that way? I can always test manually, but figured I'd see if stackoverflow knew first.
Space Engineers – How Much Space Do Large Thrusters Require?
space-engineers
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Best Answer
You're not entirely clear on what your asking, but given the numbers you're throwing out it appears you're asking about the Small Thruster for Large Grids. If that is the case the Official Space Engineer's Wiki claims that specific engine will do damage 2 (large) blocks (5m) deep directly behind the engine and, if that area is blocked, splash damage to adjacent blocks. If an Engine is one of those adjacent blocks, "Fun" ensues.
Alternatively Large Thrusters do damage 5 blocks deep (2.5m for small grids, 12.5m for large grids). The information is in a table on the bottom of the page I've linked.
I've also heard that you might want to give extra space around the exhaust path for particularly nimble ships to avoid swinging a trailing part of your craft into recently ejected exhaust.
P.S. I generally avoid wikia.com sites when there is a viable alternative, as they are generally slow to plagiarize their content from more authoritative or up-to-date sources.