A former large fire extinguisher, extinguishers are mostly the exterior of a large fire extinguisher. The inside of the container is hollow, and the sides are lined with some asbestos to absorb outside heat. The extinguisher, especially for what it breaks down to, is a very heavy junk item, and as such, isn't advised to be picked up unless the resources are absolutely needed.
If shot, an intact extinguisher will break open and produce a cloud of gray vapor. The explosion does not cause harm to bystanders.