A casualty which does not qualify as a very serious casualty and which involves a fire, explosion, grounding, contact, heavy weather damage, ice damage, hull cracking or suspected hull defect, etc., resulting in:• Structural damage rendering the marine vessel not navigable, such as penetration of the hull underwater, immobilization of main engines, extensive accommodation damage etc.; or• Pollution (regardless of quantity); and/or• A breakdown necessitating towage or shore assistance.