Question 1

Over time, wear has grooved the fixed pin your quick-release chain runs over, reducing the diameter ratio between the pin and the chain link (the D/d ratio). What's the significance of this?

Accepted Answer

A reduced D/d ratio concentrates bending stress at the point of contact, well beyond straight-line tension loads the chain is rated for — this is a known precursor to fatigue failure Cornishman's D/d ratio had worn down to as low as 3.0:1, less than half the recognised safe minimum of 7:1. The chain links nearest the pin were being bent rather than pulled in a straight line, concentrating stress at exactly the point where the fatal fracture occurred.

Question 2

You're draining a thermal oil system that was running normally a short time ago. Before opening the drain point, what should you confirm?

Accepted Answer

That the system has cooled and depressurised, and you are positioned clear of the drain point's discharge path On the dredger MV Amazone, two crew members draining a thermal oil system after months of contamination were sprayed with hot oil, suffering severe burns. The investigation found company procedures lacked clear instructions for safe drainage — confirming the system has cooled and depressurised, and standing clear of the discharge path, are essential before opening any drain point on a hot oil system.

Question 3

A thermal oil system has been contaminated and needs draining for cleaning. The written procedure tells you to open the drain valve but doesn't specify a cooling-down period or PPE. What should you do?

Accepted Answer

Treat the gap as a hazard in its own right: apply a suitable cooling/depressurising period and full PPE before proceeding, and raise the procedure gap with the Chief Engineer The FEBIMA investigation into the MV Amazone incident found that although the crew followed company procedures, those procedures lacked clear instructions for safely draining a thermal oil system. A procedure that's silent on cooling time and PPE for a hazardous task is a gap to be closed before the job starts — not a green light to skip those precautions.