spark arrester

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device designed to keep sparks from escaping, as at a chimney opening.
• noun A device used to control electric sparking at a point where a circuit is made or broken.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun electrical device to reduce sparking when electrical contacts are opened or closed
• noun a wire net to stop sparks from an open fireplace or smokestack